research paper abbreviations

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Abbreviations in Research: Common Errors in Academic Writing 

“Provided they are not obscure to the reader, abbreviations communicate more with fewer letters. Writers have only to ensure that the abbreviations they use are too well known to need any introduction, or that they are introduced and explained on their first appearance.”  

—From “The Cambridge Guide to English Usage” by Pam Peters 1  

David Crystal defines abbreviations as “a major component of the English writing system, not a marginal feature. The largest dictionaries of abbreviations contain well over half a million entries, and their number is increasing all the time.” 2 Students and researchers often use abbreviations in research writing to save space, especially when facing restrictions of page or word limits. Abbreviations in research are also used in place of long or difficult phrases for ease of writing and reading. Exactly how abbreviations in research writing should be used depends on the style guide you follow. For example, in British English, the period (or full stop) is omitted in abbreviations that include the first and last letters of a single word (e.g., “Dr” or “Ms”). But in American English, such abbreviations in writing are followed by a period (e.g., “Dr.” or “Ms.”).  

While using abbreviations in academic writing is a common feature in many academic and scientific papers, most journals prefer keeping their use to a minimum or restricting their use to standard abbreviations. As a general rule, all non-standard acronyms/abbreviations in research papers should be written out in full on first use (in both the abstract and the paper itself), followed by the abbreviated form in parentheses, as in the American Psychological Association (APA) style guide. 

Table of Contents

• Mistakes to avoid when using acronyms and abbreviations in research writing3 
• Tips to using abbreviations in research writing 

Frequently Asked Questions (FAQ)

Mistakes to avoid when using acronyms and abbreviations in research writing 3.

• Avoid opening a sentence with an abbreviation in research papers; write the word out. 
• Abbreviations such as a.m., p.m., B.C., and A.D. are never spelled out. Unless your style guide says otherwise, use lowercase or small capitals for a.m. and p.m. Use  capital letters  or small caps for B.C. and A.D. (the periods are optional).  
• Avoid RAS Syndrome:   RAS Syndrome stands for Redundant Acronym Syndrome…Syndrome. For example, DC Comics—DC already stands for “Detective Comics,” making Comics after DC redundant. 
• Avoid Alphabet Soup:   Alphabet soup refers to using too many abbreviations in academic writing. Do not abbreviate the words if their frequency of appearance in the document is less than three. 
• Do not follow acronyms with a period unless at the end of a sentence. 
• When pluralizing acronyms add a lowercase “s” at the end (“three ECGs”); acronyms can be made possessive with an apostrophe followed by a lowercase “s” (“DOD’s acknowledge”). 
• Acronyms are treated as singulars, even when they stand for plurals. Therefore, they require a singular verb (“NASA is planning to…”). 
• Articles “a” or “an” before an acronym should be based on the opening sound rather than the acronym’s meaning. This depends on whether they are pronounced as words or as a series of letters. Use “an” if a soft vowel sound opens the acronym; else, use “a.” For example, a NATO meeting; an MRI scan. 

Tips to using abbreviations in research writing

1. When to abbreviate: Using too many abbreviations in research papers can make the document hard to read. While it makes sense to abbreviate every long word, it’s best to abbreviate terms you use repeatedly. 

2. Acronyms and initialisms: Define all acronyms and initialisms on their first use by giving the full terminology followed by the abbreviation in brackets. Once defined, use the shortened version in place of the full term. 

3. Contractions: Using contractions (isn’t, can’t, don’t, etc.) in academic writing, such as a research paper, is usually not encouraged because it can make your writing sound informal. 

4. Latin abbreviations: Latin abbreviations in research are widely preferred as they contain much meaning in a tiny package. Most style manuals (APA, MLA, and Chicago) suggest limiting the use of Latin abbreviations in the main text. They recommend using etc. , e.g. , and i.e., in parentheses within the body of a text, but others should appear only in footnotes, endnotes, tables, and other forms of documentation. But APA allows using “ et al .” when citing works with multiple authors and v. in the titles of court cases. 

5. Capitalization: Abbreviations in writing are in full capital letters (COBOL, HTML, etc.). Exceptions include acronyms such as “radar,” “scuba,” and “lidar,” which have become commonly accepted words. 

6. Punctuation: Abbreviations in research can be written without adding periods between each letter. However, when shortening a word, we usually add a period as follows: 

Figure → Fig. 

Doctor → Dr. 

January → Jan. 

Note that units of measurement do not require a period after the abbreviation. But, to avoid confusion with the word “ in ,” we write “ inches ” as “ in. ” in documents. 

7. Create a list: Make a list of the abbreviations in research as you write. Adding such a list at the start of your document can give the reader and yourself an easy point of reference.  

References  

• Peters, P. The Cambridge Guide to English Usage. Cambridge University Press (2004).  
• Crystal, D. Spell it out: The singular story of English spelling (2013). 
• Nordquist, R. 10 Tips for Using Abbreviations Correctly (July 25, 2019). Retrieved from https://www.thoughtco.com/tips-for-using-abbreviations-correctly-1691738  

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Abbreviations in a research paper are shortened forms of words or phrases used to represent specific terms or concepts. They are employed to improve readability and conciseness, especially when there are strict word counts and terms are mentioned frequently throughout the paper. To ensure clarity, it is essential to define each abbreviation when it is first used in the research paper. This is typically done by providing the full term followed by its abbreviation in parentheses.

Some commonly used abbreviations in academic writing include e.g. (exempli gratia), i.e. (id est), et al. (et alia/et alii), etc. (et cetera), cf. (confer), and viz. (videlicet). Additionally, there are several subject-specific abbreviations that are known by and commonly used in a field of study. However, know that abbreviations may mean different things across different fields. This makes it important to consult style guides or specific guidelines provided by the academic institution or target publication to ensure consistent and appropriate use of abbreviations in your academic writing.

An acronym is an abbreviation formed from the initial letters of a series of words and is pronounced as a word itself. For example, NASA (National Aeronautics and Space Administration) and UNESCO (United Nations Educational, Scientific and Cultural Organization) are acronyms. An abbreviation is a shortened form of a word or phrase but they are usually pronounced as individual letters. Examples of abbreviations include “et al.” for “et alia/et alii” and “e.g.” for “exempli gratia.”

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• List of Abbreviations | Example, Template & Best Practices

List of Abbreviations | Example, Template & Best Practices

Published on 23 May 2022 by Tegan George . Revised on 25 October 2022.

A list of abbreviations is an alphabetical list of abbreviations that you can add to your thesis or dissertation. If you choose to include it, it should appear at the beginning of your document, just after your table of contents .

Abbreviation lists improve readability, minimising confusion about abbreviations unfamiliar to your reader. This can be a worthwhile addition to your thesis or dissertation if you find that you’ve used a lot of abbreviations in your paper.

If you only use a few abbreviations, you don’t necessarily need to include a list. However, it’s never a bad idea to add one if your abbreviations are numerous, or if you think they will not be known to your audience.

You can download our template below in the format of your choice to help you get started.

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• Table of contents

Example list of abbreviations

Best practices for abbreviations and acronyms, additional lists to include, frequently asked questions.

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There are a few rules to keep in mind about using abbreviations in academic writing. Here are a few tips.

• Acronyms are formed using the first letter of each word in a phrase. The first time you use an acronym, write the phrase in full and place the acronym in parentheses immediately after it. You can then use the acronym throughout the rest of the text.
• The same guidance goes for abbreviations: write the explanation in full the first time you use it, then proceed with the abbreviated version.
• If you’re using very common acronyms or abbreviations, such as UK or DNA, you can abbreviate them from the first use. If you’re in doubt, just write it out in full the first time.

As well as the list of abbreviations, you can also use a list of tables and figures and a glossary for your thesis or dissertation.

Include your lists in the following order:

• List of figures and tables
• List of abbreviations

As a rule of thumb, write the explanation in full the first time you use an acronym or abbreviation. You can then proceed with the shortened version. However, if the abbreviation is very common (like UK or PC), then you can just use the abbreviated version straight away.

Be sure to add each abbreviation in your list of abbreviations !

If you only used a few abbreviations in your thesis or dissertation, you don’t necessarily need to include a list of abbreviations .

If your abbreviations are numerous, or if you think they won’t be known to your audience, it’s never a bad idea to add one. They can also improve readability, minimising confusion about abbreviations unfamiliar to your reader.

A list of abbreviations is a list of all the abbreviations you used in your thesis or dissertation. It should appear at the beginning of your document, immediately after your table of contents . It should always be in alphabetical order.

An abbreviation is a shortened version of an existing word, such as Dr for Doctor. In contrast, an acronym uses the first letter of each word to create a wholly new word, such as UNESCO (an acronym for the United Nations Educational, Scientific and Cultural Organization).

Your dissertation sometimes contains a list of abbreviations .

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Other APA Guidelines: Abbreviations

Basics of abbreviations.

Using abbreviations can be an effective way to avoid repeating lengthy, technical terms throughout a piece of writing, but they should be used sparingly to prevent your text from becoming difficult to read.

Many abbreviations take the form of acronyms or initialisms, which are abbreviations consisting of the first letter of each word in a phrase. Examples are National Institute of Mental Health (NIMH) and Better Business Bureau (BBB). Note that the abbreviation uses all capital letters, and there are no periods between the letters.

To use an abbreviation, write out the term or phrase on first use, followed by the abbreviation in parentheses. See these examples:

The patient had been diagnosed with traumatic brain injury (TBI) in March of the previous year. Walden students need to know how to cite information using the American Psychological Association (APA) guidelines.

Using an Abbreviation in a Draft

After introducing the abbreviation, use the abbreviation by itself, without parentheses, throughout the rest of the document.

The patient had been diagnosed with traumatic brain injury (TBI) in March of 2014. According to the Centers for Disease Control and Prevention (CDC, 2015), people with TBI often have difficulty with memory and concentration, physical symptoms such as headaches, emotional symptoms such as sadness and irritability, and difficulty falling asleep. Although the patient explained that she experienced frequent headaches and difficulty concentrating, she had not been regularly taking any medication for her TBI symptoms when she visited the clinic 6 months after her diagnosis.

Note: When introducing an abbreviation within a narrative citation, use a comma between the abbreviation and the year.

Making an Abbreviation Plural

Simply add an “s” to an abbreviation to make it plural. (Do not add an apostrophe.)

I work with five other RNs during a typical shift.

Note: RN is a commonly used acronym found in Merriam-Webster’s Dictionary , so it does not need to be introduced. See the “Exceptions to the Rules” section below for more information about commonly used abbreviations.

Exceptions to the Rules

There are a few exceptions to the basic rules:

• If you use the phrase three times or fewer, it should be written out every time. However, a standard abbreviation for a term familiar in its abbreviated form is clearer and more concise, even if it is used fewer than three times.
• Commonly used acronyms and abbreviations may not need to be written out. If an abbreviation appears as a word in Merriam-Webster’s Collegiate Dictionary , then it does not need to be written it out on first use. Examples include words such as IQ, REM, and HIV.
• Other than abbreviations prescribed by APA in reference list elements (e.g., “ed.” for “edition,” “n.d.” for “no date,” etc.), do not use abbreviations in the references list. For example, a source authored by the Centers for Disease Control and Prevention would not be abbreviated as CDC in the references list.
• If using an abbreviation for a unit of measure with a numerical value, you do not need to write the term out on first use. For example, instead of writing “12 grams;” you can simply use “12 g.” If, however, you use a unit of measure without a numerical value, write the term out (e.g., “several grams”).
• Abbreviations for time, common Latin terms, and statistical abbreviations also follow specific rules. See APA 7, Sections 6.28, 6.29, and 6.44 for more information.

United States and U.S.

In APA style, "United States" should always be spelled out when it is used as a noun or location.

Example: In the United States, 67% reported this experience.

United States can be abbreviated as "U.S." when it is used as an adjective.

Examples: U.S. population and U.S. Census Bureau.

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Using abbreviations in scientific papers

It’s time to know more about abbreviations in scientific papers and learn ways to avoid mistakes when using them.

The use of abbreviations in academic and scientific publications is common, but authors are often asked to keep their usage as brief as possible. 

They are usually limited to universal abbreviations for weights and measurements. We would like to provide some tips in this article on how to use abbreviations effectively in your writing. 

If you are going to use abbreviations in scientific papers , then you should pay attention to the following tips.

What do abbreviations in scientific papers mean?

Abbreviations are shortened versions of terms and phrases, such as kg for kilograms, CEO for chief executive officer and Dr. for doctors. The use of abbreviations is ideally suited to situations in which you wish to reduce the number of words the text contains. 

However, there is a tendency for abbreviations to be widely used in one field of study but unknown in another. It is important to use the article that corresponds to the pronounced form of the abbreviation 

Are abbreviations allowed in research papers and where do you put them?

Your paper should include a list of abbreviations at the beginning of each of the following segments: heading, abstract, text, and figure/table legends. 

A common rule of thumb is to write all non-standard abbreviations in their entirety on their first appearance both in abstracts and papers themselves. 

After the first mention of an abbreviation, it is essential that you use it frequently. Additionally, the format should be consistently followed throughout the paper. 

Abbreviations and acronyms: what’s the difference?

The terms abbreviation and acronym are both shorthand versions of words and phrases. While abbreviations shorten longer words (like Dr. or Prof.), acronyms use the first letter of each word in a phrase to create a new word (like NASA or FBI). 

There is a difference between abbreviations and acronyms, even though authors often use them the same way. An acronym, initialism, or other word contraction form is an abbreviation. 

Acronyms are abbreviations formed by condensing the first letters of multiple words into one. Although not all abbreviations are acronyms, all acronyms are abbreviations. Abbreviations and acronyms differ primarily in this regard.

The most common mistakes to avoid when using abbreviations

Abbreviation errors in academic publications are sometimes common. The following are a few ways you can avoid this from happening in the future. 

• It is usually advisable to define abbreviations only once when you decide to use them. Exceptions do exist, however. An abbreviation may be used at the beginning of a section in a report or chapter in a book.
• Having an inconsistent approach is the top mistake you can make. The journals will provide guidelines on how to submit your work, so please read them carefully. Generally, abbreviations in scholarly articles are introduced only after three or more instances of the term.
• It is important to use standard abbreviations if you are writing in a field that uses them – for instance, elements in the physical sciences are often abbreviated for word count constraints. Standard formatting should always be used (both spelling and case-sensitive formatting). Capitalization is typically used only for proper nouns.
• Remember that for well-known abbreviations, lowercase is recommended over uppercase for competing terms, if the same letters are used in other abbreviations in the manuscript.
• The abbreviation “et al.” can be confusing to use in scientific writing because it is often misspelt or misused. As the name suggests, this term means “and others”. In-text citations or references are often shortened with this abbreviation, and it can be used wherever it precedes a name in the text. 

Here is a list of some scientific abbreviations

And the list goes on.

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List of Abbreviations for a Thesis or Dissertation

• By DiscoverPhDs
• September 14, 2020

What are Abbreviations and Acronyms?

An abbreviation is a shortened version of a term or phrase, e.g. kg for kilogram or Dr. for doctor.

An acronym is a type of abbreviation constructed from the first letters of a term, e.g. FRP for Fibre Reinforced Polymer or STEM for Science, Technology, Engineering and Maths.

List of Abbreviations in a Thesis or Dissertation

If your thesis or dissertation contains several symbols or abbreviations, it would be beneficial to include a list of abbreviations to assist your reader. This is a list sorted in alphabetical order that gives their definitions.

This will not only help the reader better understand your research, but it will also improve the flow of your paper, as it prevents continually having to define abbreviations in your main text.

Where Does a List of Abbreviations Go?

When including a list of abbreviations, insert them near the start of the report after your table of contents. To make it clear that your document contains an abbreviated list, also add a separate heading to your table of contents.

Note: The page number for your list of abbreviations should continue from the page number that proceeds it; there is no need to reset it for this section.

Rules for Using Abbreviations and Acronyms

The first time you use an abbreviation or acronym, it is good practice to write out the full terminology or phrase followed by the abbreviation or acronym encased in parenthesis.

After defining an abbreviation or acronym for the first time in your main text, you no longer need to use the full term; for example:

Example of Acronyms in a Thesis or Dissertation

This allows the reader to understand your report without having to rely on the list of abbreviations; it is only there to help the reader if they forget what an abbreviation stands for and needs to look it up.

Note: In academic writing, abbreviations that are not listed should always be defined in your thesis text at their first appearance.

Abbreviated Exceptions

Very common abbreviations should not be included in your list because they needlessly overload your list with terms that your readers already know, which discourages them from using it.

Some examples of common abbreviations and acronyms that should not be included in your standard abbreviation list are USA, PhD , Dr. and Ltd. etc.

Example of List of Abbreviations for a Thesis or Dissertation

An example abbreviation list is as follows:

The above example has been extracted from here .

List of Symbols

You can add symbols and their definitions to your list of abbreviations, however, some people like to keep them separate, especially if they have many of them. While this format will come down to personal preference, most STEM students create a separate list of symbols and most non-STEM students incorporate them into their list of abbreviations.

Note: If you are writing your report to APA style, you will need to consider additional requirements when writing your list of abbreviations. You can find further information here .

Further Reading

Whether you’re writing a Ph.D. thesis or a dissertation paper, the following resources will also be of use:

• Title Page for an Academic Paper
• List of Appendices

Finding a PhD has never been this easy – search for a PhD by keyword, location or academic area of interest.

Choosing a good PhD supervisor will be paramount to your success as a PhD student, but what qualities should you be looking for? Read our post to find out.

A well written figure legend will explain exactly what a figure means without having to refer to the main text. Our guide explains how to write one.

The unit of analysis refers to the main parameter that you’re investigating in your research project or study.

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An abstract and introduction are the first two sections of your paper or thesis. This guide explains the differences between them and how to write them.

An academic transcript gives a breakdown of each module you studied for your degree and the mark that you were awarded.

Nina’s in the first year of her PhD in the Department of Psychology at the University of Bath. Her project is focused on furthering our understanding of fatigue within adolescent depression.

Eleni is nearing the end of her PhD at the University of Sheffield on understanding Peroxidase immobilisation on Bioinspired Silicas and application of the biocatalyst for dye removal.

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List of abbreviations

Microsoft Word can automatically create a List of Abbreviations and Acronyms. If you use a lot of abbreviations and acronyms in your thesis — and even if you only use a few — there is no reason not to include a list. The process is not at all difficult. See the video tutorial below to see how to create such a list.

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Acronyms and Abbreviations

Ramón ribes.

1_16 Serv. Radiología, Hospital Reina Sofia, 14005 Córdoba, Spain

Palma Iannarelli

2_16 University College London, Gower Street, London, WC1E 6BT United Kingdom

Rafael F. Duarte

3_16 Inst. Català d’Oncologia Servicio de Hematología Clinica, Hospital Duran i Reynals, Av. Gan Via s/n km 2.7, 08907 Barcelona, Spain

n many fields today abbreviations and acronyms are common. They provide a useful tool for shortening long words or expression in order to save time and space. Some well-known general examples are DVD (digital versatile disc), UNICEF (United Nations International Children’s Emergency Fund), NASA (National Aeronautics and Space Administration), and UN (United Nations). Abbreviations are extensively used in the scientific and medical communities. It is common practice to use abbreviations for long names of many clinical diseases and procedures, and for scientific techniques that have to be repeated many times in medical or scientific papers, posters, and oral presentations. This can cause substantial communication difficulties for individuals who are not familiar with English abbreviations in their field. The example below is meaningless to individuals who are not familiar with the abbreviations used.

In many fields today abbreviations and acronyms are common. They provide a useful tool for shortening long words or expression in order to save time and space. Some well-known general examples are DVD (digital versatile disc), UNICEF (United Nations International Children’s Emergency Fund), NASA (National Aeronautics and Space Administration), and UN (United Nations). Abbreviations are extensively used in the scientific and medical communities. It is common practice to use abbreviations for long names of many clinical diseases and procedures, and for scientific techniques that have to be repeated many times in medical or scientific papers, posters, and oral presentations. This can cause substantial communication difficulties for individuals who are not familiar with English abbreviations in their field. The example below is meaningless to individuals who are not familiar with the abbreviations used.

For example,

IHC study of CNS tissue from MS subjects demonstrated loss of PLP-expressing OLs.

Many individuals, including native English speakers, do not know the difference between an acronym and an abbreviation. Acronyms and abbreviations are formed by combining the first letter or letters of several words. All acronyms are abbreviations, but not all abbreviations are acronyms. An acronym is a special type of abbreviation that can be pronounced as a single word (it can be said), while all other abbreviations are pronounced letter by letter (you say each letter individually or spell it out).

AIDS is an acronym for A cquired I mmune D eficiency S yndrome because you say the abbreviation as a word (“aydz”); whereas HIV is an abbreviation for H uman I mmunodeficiency V irus (in this case you say each letter individually).

It can be extremely frustrating and time-consuming trying to find out what certain commonly used acronyms and abbreviations mean. Abbreviations that some consider universally known may be obscure to others. In addition, shortened forms used in one country may not be understood in another. In order to eliminate guesswork and prevent frustration, we have put together an alphabetized list of the most commonly used English acronyms and abbreviations in biomedical research. We feel that having a central reference list at your fingertips could be quite helpful for your scientific communications.

Abbreviation Rules and Style Conventions in English

Apply the following guidelines when using abbreviations:

Oligodendrocytes (OLs) are the cells responsible for producing a fatty protein called myelin. Each OL can supply myelin for several axons and each axon can be supplied by several OLs.

PCRs ( not PCR’s)

BACs ( not BAC’s)

Drs. ( not Dr’s)

rbc’s ( not rbcs)

Exception 1 : Plurals of some abbreviations, particularly in references, are not formed by merely adding an s.

p for page and pp for pages ( not ps or pgs)

l for line and ll for lines ( not ls)

c for column and cc for columns ( not cs)

Exception 2 : Singular and plural units of measure are abbreviated the same. An s is generally not added to the plurals.

1 km and 5 km ( not 5 kms)

Exception 3 : If the abbreviation contains a period (full stop), form the plural with an apostrophe and an s (’s). This is probably because it looks more awkward without apostrophes:

Ph.D.’s

M.D.’s

Exception 4 : Plurals of single-letter abbreviations are formed by adding [’s].

X’s

EMBO’s homepage

The United Nations International Children’s Emergency Fund is a voluntarily funded agency.

UNICEF was created on December 11, 1946.

an mRNA molecule - although “m” is a consonant, we use the an article because the first sound we make is an “em” sound.

an X-ray - this abbreviation begins with a consonant letter, but sounds like it starts with a vowel. The first sound we make is an “eks” sound.

There are several abbreviation styles used today. The only rule one should remember is to have a consistent style.

AIDS, NATO, BBC, and SARS

However, some acronyms are no longer capitalized. Examples are laser, radar and sonar.

• A period is sometimes written after an abbreviated word (there is no strict rule). The general modern trend is to omit periods from abbreviations (to avoid an appearance of clutter).

Organizations, countries, and units of measure are not generally followed by periods.

EU ( not E.U.)

UN ( not U.N.)

IBM ( not I.B.M.)

5 mg ( not 5 mg.)

Periods are optional with degree titles (this is a matter of preference). However, in modern usage, periods are usually omitted.

Examples where both forms are acceptable:

PhD or Ph.D.

BSc or B.Sc.

The technician will be here at 4 p.m.

not The technician will be here at 4 p.m.

………………AIDS ………………10 mg

not ……………AI not ………………10

List of abbreviations and Latin expressions used in scientific writing

General Abbreviations and Acronyms Used in Biomedical Research

Abbreviations definition.

Please note that amino acids are given three-letter and one-letter abbreviations (e.g. A or Ala for Alanine).

Methods and Techniques Used in Biomedical Research

Radioactive isotopes, units of measurement.

Always abbreviate units when reporting numerical information. However, if you write the number out in full, you must spell out the unit of measurement. Always put a space between the number and the unit. When starting a sentence with a number and unit, both must be spelled out as words. Abbreviations for most units of measurement use small letters. The following abbreviations of units of measurement are frequently used in biomedical research.

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MLA Abbreviations

Welcome to the Purdue OWL

This page is brought to you by the OWL at Purdue University. When printing this page, you must include the entire legal notice.

Copyright ©1995-2018 by The Writing Lab & The OWL at Purdue and Purdue University. All rights reserved. This material may not be published, reproduced, broadcast, rewritten, or redistributed without permission. Use of this site constitutes acceptance of our terms and conditions of fair use.

There are a few common trends in abbreviating that you should follow when using MLA, though there are always exceptions to these rules. For a complete list of common abbreviations used in academic writing, see Appendix 1 in the MLA Handbook (9 th  ed.).

Uppercase letter abbreviations

Do not use periods or spaces in abbreviations composed solely of capital letters, except in the case of proper names:

unless the name is only composed of initials:

Lowercase letter abbreviations

Use a period if the abbreviation ends in a lowercase letter, unless referring to an Internet suffix, where the period should come before the abbreviation:

Note: Degree names are a notable exception to the lowercase abbreviation rule.

Use periods between letters without spacing if each letter represents a word in common lowercase abbreviations:

Other notable exceptions:

Abbreviations in citations

Condense citations as much as possible using abbreviations.

Time Designations

Remember to follow common trends in abbreviating time and location within citations. Month names longer than four letters used in journal and magazine citations should be abbreviated:

Geographic Names

Use geographic names of states and countries. Abbreviate country, province, and state names.

Scholarly Abbreviations

The MLA Handbook (9 th ed.) encourages users to adhere to the common scholarly abbreviations for both in-text citations and in the works-cited page. Here is the list of common scholarly abbreviations from Appendix 1 of the MLA Handbook (9 th ed.) with a few additions:

• anon. for anonymous
• app. for appendix
• bk. for book
• c. or ca. for circa
• ch. for chapter
• col. for column
• def. for definition
• dept. for department
• e.g. for example
• ed. for edition
• et al. for multiple names (translates to "and others")
• etc. for "and so forth"
• fig. for figure
• fwd. for foreword
• i.e. for that is
• jour. for journal
• lib. for library
• MS, MSS for manuscript(s)
• no. for number
• P for Press (used for academic presses)
• p. for page, pp. for pages
• par. for paragraph when page numbers are unavailable
• qtd. in for quoted in
• rev. for revised
• sec. or sect. for section
• ser. for series
• trans. for translation
• U for University (for example, Purdue U)
• UP for University Press (for example, Yale UP or U of California P)
• vers. for version
• var. for variant
• vol. for volume

Publisher Names

Cite publishers’ names in full as they appear on title or copyright pages. For example, cite the entire name for a publisher (e.g. W. W. Norton or Liveright Publishing).

Exceptions:

• Omit articles and business abbreviations (like Corp., Inc., Co., and Ltd.).
• Use the acronym of the publisher if the company is commonly known by that abbreviation (e.g. MLA, ERIC, GPO). For publishers who are not known by an abbreviation, write the entire name.
• Use only U and P when referring to university presses (e.g. Cambridge UP or U of Arkansas P)

For more information on scholarly abbreviations, see Appendix 1 of the MLA Handbook (9 th  ed.) . See also the following examples:

• How it works

List of Abbreviations for Dissertation

Published by Owen Ingram at August 11th, 2021 , Revised On August 22, 2023

What are Abbreviations?

“Oxford English Dictionary defines an abbreviation as ‘a short form of a word’. For example, UN is the short form – an abbreviation – for United Nations.” Abbreviations are commonly used in every form of writing, including academic writing. Abbreviations in dissertations generally have to do with names of organisations, institutions, theoretical models and the like. 

If your dissertation includes many abbreviations, it will make sense to define all these abbreviations in an alphabetically-organised list. 

This can really help your readers understand the jargon and specific terms they might not be familiar with. Here is all you need to know about the  list of abbreviations for the dissertation .

Placement of a List of Abbreviations 

Abbreviations’ list should be placed at the start of the dissertation and right after the  table of contents . The list of abbreviations should also be a part of the table of contents. If you aren’t using many abbreviations, there isn’t a need to include a whole list. Underneath, we will guide you on how to define abbreviations within the text.

Abbreviations don’t need to be numbered in the list.

Acronyms and Abbreviations

There are various ways of placing acronyms and abbreviations in a dissertation. While using acronyms formed by combining the first letter of each word from a phrase, you should write that phrase in its full form and then write the abbreviation in parenthesis right after that. You can then make use of that acronym for the  rest of the dissertation .

Acronyms Example in a dissertation

 I met the regional sales manager (RSM) of 5 different multi-national companies (MNC). I conducted in-depth interviews with the RSM, through which I came to know that every MNC  has a different strategy for its product marketing.

Some exceptions don’t apply to this rule, such as when acronyms like AI, URL, FIFA, etc. are involved You can still write the full acronym if unsure.

Point to remember: In research, it is not considered right to create your own abbreviations and/or acronyms. You can only abbreviate terms that have officially been abbreviated in books, journals and other published materials. For instance, you cannot abbreviate ‘women leaders in private sectors’ to ‘WLiPS’. Unless such an abbreviation actually exists, this would be unethical in the context of research.

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APA Style of Abbreviations

If you are working with APA referencing style, there are additional and specific requirements for creating a list of abbreviations for the dissertation.

Other Types of Lists in a Dissertation

In addition to the list of abbreviations, there are other lists that you can include in your dissertation paper, including:

• Table of Contents
• Figures and tables

Point to note: You might come across some types of research or theses where the abbreviations’ column is placed in front of an ‘explanation’ column. The latter is simply another way of ‘defining’ the acronyms/abbreviations or rather, giving their full forms. Here is an example of such a list of abbreviations from a thesis:

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Frequently Asked Questions

What is a list of abbreviations.

A list of abbreviations is a compilation of shortened forms used in a document, often found at the beginning or end. It explains the meanings of acronyms, initialisms, or shortened terms to help readers comprehend the text more easily.

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When writing your dissertation, an abstract serves as a deal maker or breaker. It can either motivate your readers to continue reading or discourage them.

Have you failed dissertation, assignment, exam or coursework? Don’t panic because you are not alone. Get help from our professional UK qualified writers!

Here are the steps to make a theoretical framework for dissertation. You can define, discuss and evaluate theories relevant to the research problem.

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Clinical Research Acronyms and Abbreviations You Should Know

We all know there are numerous acronyms and abbreviations used in clinical research. While some can be easily deciphered, others may take some searching to find their meaning. Particularly with the recent surge in electronic systems and regulations, it can be hard to keep track of necessary abbreviations and terms.

Whether you’re new to the clinical research world or need a refresher, here’s a condensed list of common acronyms and abbreviations you may come across.

AACI: Association of American Cancer Institutes

AAHRPP: Association for the Accreditation of Human Research Protection Programs

ABSA: Association of Biosafety and Biosecurity

ACRP: Association of Clinical Research Professionals

ACTS: Association for Clinical and Translational Science

ADME: Absorption, Distribution, Metabolism, and Elimination

ADR: Adverse Drug Reaction

AE: Adverse Event

ALCOA:  Attributable, Legible, Contemporaneous, Original, Accurate

AMC: Academic Medical Center

API: Active Pharmaceutical Ingredient

API: Application Program Interface

ARO: Academic Research Organization

ASCO: American Society of Clinical Oncology

ASCPT: American Society for Clinical Pharmacology and Therapeutics

ASGCT: American Society of Gene & Cell Therapy

BA/BE: Bioavailability/Bioequivalance

BLA: Biological Licensing Application

BSM: Biospecimen Management

caBIG: Cancer Biomedical

CAPA:  Corrective and Preventive Action

CAR-T: Chimeric Antigen Receptors and T cells

CBER: Center for Biologics Evaluation and Research

CBRN: California Board of Registered Nursing

CCEA: Complete, Consistent, Enduring, Available

CCOP: Community Clinical Oncology Program

CCR: Center for Cancer Research

CCSG: Cancer Center Support Grant

CCTO or CTO: Centralized Clinical Trials Office or Clinical Trials Office

CDASH:  Clinical Data Acquisition Standards Harmonization

CDER: Center for Drug Evaluation and Research

CDM: Clinical Data Management

Related article: “Improve Data Quality with 5 Fundamentals of Clinical Data Management”

CDP: Clinical Development Plan

CDRH: Center for Devices and Radiological Health

CDS: Clinical Data System

CDUS: Clinical Data Update System

CFR: Code of Federal Regulations

CMO: Contract Manufacturing Organization

CMS: Centers for Medicare & Medicaid Services

CRA: Clinical Research Associate

CRC: Clinical Research Coordinator

Related article: “Deciphering the CRC Career Path: Key Skills and Responsibilities”

CRF: Case Report Form

CRMS: Clinical Research Management System

CRO: Contract Research Organization

CRPC: Clinical Research Process Content

CSO:  Contract Safety Organization

CSR: Clinical Study Report

CTA: Clinical Trial Authorization

CTCAE: Common Terminology Criteria for Adverse Events

CTMS: Clinical Trial Management System

CTRP: Clinical Trials Reporting Program

CTSA: Clinical and Translational Science Award

DDI: Drug-Drug Interaction

DHHS: Department of Health and Human Services

DM: Data Manager

DMC: Data Monitoring Committee

DSMB: Data and Safety Monitoring Board

EC: Ethics Committee

eCOA: Electronic Clinical Outcome Assessment

eCRF: Electronic Case Report Form

EDC: Electronic Data Capture

Learn more about Advarra’s electronic data capture system, Advarra EDC .

EHR: Electronic Health Record

EMR: Electronic Medical Record

ePRO: Electronic Patient-Reported Outcomes

eTMF: Electronic Trial Master File

FAIR: Findable, Accessible, Interoperable, Reusable

FDA: Food and Drug Administration

FE: Food Effect

FIH: First In Human

FWA: Federalwide Assurance

GCP: Good Clinical Practice

GCRC: General Clinical Research Center

GDP:  Good Documentation Practice

GLP: Good Laboratory Practice

GMP: Good Manufacturing Practice

GVP: Good Pharmacovigilance Practice

HIPAA: Health Insurance Portability and Accountability Act

HRPP: Human Research Protection Program

IBC: Institutional Biosafety Committee

ICF: Informed Consent Form

ICH: International Council for Harmonization

IDE: Investigational Device Exemptions

IEC: Independent Ethics Committee

IHCRA: In House Clinical Research Associate

IIT: Investigator Initiated Trial

IND: Investigational New Drug (Application)

IP: Investigational Product

IRB: Institutional Review Board

ITT: Intent to Treat

IVRS: Interactive Voice Response System

IWRS: Interactive Web Response System

LTFU: Long Term Follow Up

LRAA: Local Regulatory Affairs Associate

MAC: Medicare Administrative Contractor

MAD: Multiple Ascending Dose

MCA: Medicare Coverage Analysis

Related webinar: Build a Better Budget: Using Medicare Coverage Analysis to Streamline Study Startup .

MRN: Medical Record Number

NCI: National Cancer Institute

NDA: New Drug Application

NHV: Normal Healthy Volunteer

NIH: National Institutes of Health

NLM: National Library of Medicine

OCT: Office of Clinical Trials

OHRP: Office for Human Research Protections

OSR: Outside Safety Report

PAC: Post Approval Commitments

PC: Protocol Coordinator

PD: Protocol Director

PHI:  Protected Health Information

PI: Principal Investigator

PK/PD: Pharmacokinetic/Pharmacodynamic

PRE: Prompt Reporting Event

PRMC: Protocol Review and Monitoring Committee

PRMS: Protocol Review and Monitoring System

QC: Quality Control

QCT: Qualifying Clinical Trial

QMS: Quality Management System

SAD: Single Ascending Dose

SAE: Serious Adverse Event

SC: Study Coordinator

SDR: Source Document Review (Also Source Data Review)

SDTM:  Study Data Tabulation Model

SDV: Source Document Verification

SIF: Site Investigator File

SMO: Site Management Organization

SOC: Standard of Care

SOE: Schedule of Events

SOP: Standard Operating Procedure

Related article: “Data Collection in Clinical Trials: 4 Steps for Creating an SOP”

SPOREs: Specialized Programs for Research Excellence

SRB: Scientific Review Board

SRC: Scientific Review Committee

SUSAR: Suspected Unexpected Serious Adverse Reaction

SVT: Subject Visit Template

TMF: Trial Master File (also eTMF)

TMO: Trial Management Organization

UADE: Unanticipated Adverse Device Effect

UADR: Unexpected Adverse Drug Reaction

UAP: Unanticipated Problem

Is there an abbreviation or acronym you see regularly in clinical research that isn’t listed here? Let us know .

To learn more about the fundamentals of clinical research, check out these free resources:

• Improve Data Quality with 5 Fundamentals of Clinical Data Management
• Beginner’s Guide to Clinical Trial Performance Metrics
• Deciphering the CRC Career Path: Key Skills and Responsibilities

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Abbreviations and Acronyms

The acronyms on this page are commonly used across research, especially human subject research. Asterisks (*) indicate that the acronym is specific to the University of Rochester.

You can also download a printable version of this guide for your records.

• AAHRPP: Association for the Accreditation of Human Research Protection Programs  
• AARC*: Administrative Research Review Committee (Highland Hospital)  
• ACRP: Association of Clinical Research Professionals  
• Adverse Drug Event
• Adverse Drug Experience  
• ADME: Absorption, Distribution, Metabolism, and Elimination
• ADR: Adverse Drug Reaction  
• AE: Adverse Event  
• ALCOAC: Accurate, Legible, Contemporaneous, Original, Attributable, and Complete  
• ARO: Academic Research Organization
• BAA: Business Associates Agreement  
• BA/BE: Bioavailability/Bioequivalence
• BIMO: Bioresearch Monitoring Program (FDA)  
• CABIN*: Center for Advanced Brain Imaging & Neurophysiology (formerly Rochester Center for Brain Imaging)  
• CAPA: Corrective and Preventative Action  
• CART*: Center for Advanced Research Technologies
• CBER: Center for Biologics Evaluation and Research (FDA)  
• CCEA: Complete, Consistent, Enduring, Available
• CCRA: Certified Clinical Research Associate  
• CCRC: Certified Clinical Research Coordinator  
• CCRP: Certified Clinical Research Professional  
• CDER: Center for Drug Evaluation and Research (FDA)  
• CDP: Clinical Development Plan
• CDS: Clinical Data System
• CEL*: Center for Experiential Learning  
• CFR: Code of Federal Regulations  
• CHeT*: Center for Health and Technology  
• CISCRP: Center for Information and Study on Clinical Research Participation  
• CIOMS: Council for International Organizations of Medical Sciences  
• cIRB: Central Institutional Review Board  
• CITI: Collaborative Institutional Training Initiative  
• CLIA: Clinical Laboratory Improvement Amendments  
• CME : Continuing Medical Education
• CMSU*: Clinical Materials Service Unit  
• CoC: Certificate of Confidentiality
• COI: Conflict of Interest  
• CPI: Certified Principal Investigator  
• CR*: Continuing Review (Click IRB)  
• CRA: Clinical Research Associate  
• Clinical Research Center* (CTSI)
• Clinical Research Coordinator  
• CRF: Case Report Form  
• CRO: Clinical Research Organization  
• CSR: Clinical Study Report  
• CT: Clinical Trial  
• CTA: Clinical Trial Agreement  
• CTCC*: Clinical Trials Coordination Center  
• CTM: Clinical Trial Material  
• CTMS: Clinical Trial Management System  
• CTO*: Clinical Trial Office (Cancer Center)  
• CTSI*: Clinical & Translation Science Institute  
• CTTI: Clinical Trials Transformation Initiative  
• CV: Curriculum Vitae  
• DB: Double Blind  
• Data Correction Form  
• Data Clarification Form  
• DHHS (HHS): Department of Health & Human Services  
• DM: Data Manager
• DMC: Data Monitoring Committee  
• DMP: Data Management Plan  
• DROIPR*: Department of Radiation Oncology Protocol Review Committee  
• DSMB: Data and Safety Monitoring Board  
• DSMP: Data and Safety Monitoring Plan  
• DUA: Data Use Agreement  
• EAC: Endpoint Adjudication Committee
• Ethics Committee  
• European Commission  
• ECI: Event of Clinical Interest  
• eCRF: Electronic Case Report Form  
• EDC: Electronic Data Capture  
• EDRA*: Emergency Department Research Associate  
• EHR: Electronic Health Record  
• EIR: Establishment Inspection Report  
• EMR: Electronic Medical Record  
• EMRC*: Emergency Medicine Research Committee  
• ePRO: Electronic Patient Reported Outcomes  
• eTMF: Electronic Trial Master File  
• fCOI: Financial Conflict of Interest
• FDA: Food and Drug Administration  
• FERPA: Family Educational Rights and Privacy Act
• FWA: Federalwide Assurance  
• GCP: Good Clinical Practice  
• GDP: Good Documentation Practice
• GDPR: General Data Protection Regulations (European Union)
• GLP: Good Laboratory Practice  
• GMP: Good Manufacturing Practice  
• HIPAA: Health Insurance Portability & Accountability Act  
• HRPP: Human Research Protection Program  
• HSP: Human Subject Protection
• HUD: Humanitarian Use Device  
• HURC*: Human Use of Radiation Committee  
• IB: Investigator’s Brochure  
• IBC: Institutional Biosafety Committee  
• ICF: Informed Consent Form  
• ICH: International Conference on Harmonisation  
• IDE: Investigational Device Exemption  
• IDMC: Independent Data Monitoring Committee  
• IDS*: Investigational Drug Service  
• IEC: Independent Ethics Committee  
• IIT: Investigator-Initiated Trial
• IND: Investigational New Drug  
• INDSR: Investigational New Drug Safety Report  
• IO: Institutional Official  
• IORA*: Integrated Online Research Administration  
• IP: Investigational Product  
• IRB: Institutional Review Board  
• IRBC*: Institutional Review Board Coordinator  
• IRBD*: Institutional Review Board Director  
• ISO: International Standards Organization
• ITT: Intent to Treat
• IVRS: Interactive Voice Response System  
• IWRS: Interactive Web Response System  
• LAR: Legally Authorized Representative  
• LDS: Limited Data Set  
• LTFU: Long Term Follow Up
• MAC: Medicare Administration Contractor
• MCA: Medicare Coverage Analysis
• MOD*: Modification (Click IRB)  
• MOD/CR*: Modification & Continuing Review (Click IRB)  
• MOO: Manual of Operations  
• MOP: Manual of Procedures  
• MRCT: Multi-Regional Clinical Trials Center  
• MSS: Multi-Site Study  
• MTA: Material Transfer Agreement  
• NAF: Notice of Adverse Findings  
• NAI: No Action Indicated  
• NCD: National Coverage Determination
• NCTG*: Neonatal Clinical Trials Group  
• NDA: New Drug Application  
• NOA: Notice of Award
• NTF: Note to File  
• OAI: Official Action Indicated  
• Office of Civil Rights  
• Office of Clinical Research * (CTSI)
• OHRP: Office for Human Research Protections  
• OHSP*: Office for Human Subject Protection  
• OIG: Office of the Inspector General
• ORACS*: Office of Research Accounting and Costing Standards  
• ORC*: Obstetrical Research Committee  
• ORPA*: Office of Research & Project Administration  
• ORS*: Office of Regulatory Support (CTSI)
• OSMB: Observational Study Monitoring Board  
• OVPR*: Office of the Vice President for Research  
• PAC: Post-Approval Consultation
• PD: Pharmacodynamic  
• PHI: Protected Health Information  
• PHS: Public Health Service  
• PI: Principal Investigator  
• PIPL: Personal Information Protection Law (China)
• PK/PD: Pharmacokinetic/Pharmacodynamic
• PM: Project Manager  
• PMA: Premarket Approval  
• PRIM&R: Public Responsibility in Medicine and Research  
• PRO: Patient Reported Outcomes  
• PROMIS: Patient Reported Outcomes Measurement Information System  
• pSite: Participating Site
• QA: Quality Assurance  
• QC: Quality Control  
• QCT: Qualifying Clinical Trial
• QI: Quality Improvement  
• QMP: Quality Management Plan
• RBM: Risk Based Monitoring  
• RCT: Randomized Controlled Trial  
• RCR: Responsible Conduct of Research
• RDE: Remote Data Entry  
• REB: Research Ethics Board  
• RHIO: Rochester Regional Health Information Organization
• RNI*: Reportable New Information (Click IRB)  
• ROPI: Report of Prior Investigations  
• RSA: Research Subject Advocate  
• RSRB*: Research Subjects Review Board  
• SADE: Serious Adverse Drug Experience  
• SAE: Serious Adverse Event  
• Safety Cohort  
• Study Coordinator  
• Subcutaneous  
• SCORE*: Study Coordinators Organization for Research & Education  
• SCRS: Society for Clinical Research Sites  
• SDV: Source Document Verification  
• sIRB: Single Institutional Review Board  
• SMO: Site Management Organization  
• SO: Safety Officer  
• SOC: Standard of Care
• SOCRA: Society of Clinical Research Associates  
• SOE: Schedule of Events
• SOP: Standard Operating Procedure  
• SUSAR: Suspected Unexpected Serious Adverse Reaction  
• TMF: Trial Master File  
• TMO: Trial Management Organization
• UADE: Unanticipated Adverse Device Effect  
• UADR: Unanticipated Adverse Drug Reaction
• UAP: Unanticipated Problem  
• UPIRTSO: Unanticipated Problem Involving Risk to Subjects or Others  
• VAI: Voluntary Action Indicated  
• WCG: WIRB Copernicus Group
• WCI PRMC*: Wilmot Cancer Institute Protocol Review and Monitoring Committee
• WIRB: Western Institutional Review Board

*Specific to the University of Rochester

Research and Verification of Unified Yield Surface SFG Model considering Temperature Influence

• Geotechnical Engineering
• Published: 22 April 2024

Cite this article

• Xiao-wen Liu 1 ,
• Ze-ming Wu 1 &
• Hai-lin Luo 1  

13 Accesses

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When unsaturated soils are affected by thermal radiation such as sunlight, geothermal heat, nuclear waste, and biochemical reactions, the soil temperature will increase and accelerate soil moisture migration, resulting in soil deformation. Therefore, in this paper, by extending the SFG model of the unified yield surface to consider the effect of temperature change on the unified yield surface, a yield surface constitutive model which can simultaneously reflect temperature-suction-stress is proposed. In order to verify the applicability of the model, the triaxial test of Jiangxi laterite at different temperatures is carried out to determine the calculation parameters of the model, and the fitting results of the model are compared with the experimental results, and the model is fitted and analyzed by referring to the test data of remolded clay used by Uchaipichat. The results show that the model can well reflect the stress-strain characteristics of soil during compression rebound, dehumidification and shear at different temperatures, which provides a theoretical support for predicting and solving the influence of temperature change on the stress deformation and shear strength of unsaturated soil in the corresponding engineering environment in the future, thus further enriching the constitutive theory of unsaturated soil under the influence of temperature.

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Thermo-elastoplastic constitutive model for unsaturated soils.

A Modified Two-Surface Plasticity Model for Saturated and Unsaturated Soils

Elasto-Plastic Constitutive Model for Unsaturated Soils with Subloading Surface Concept

Abbreviations.

Elastic strain

The plastic scalar factor

Temperature produces elastic strain on soil

Temperature produces plastic strain on soil

The elastic-plastic compression index caused by temperature change

The resilience index of v-lnp

The suction influence rebound index

The slope of the critical state line

Related parameter introduced to control the yield surface, and the value range is 10 −2 –10 −8 Mpa

The initial net stress

The preconsolidation stress of the initial yield surface

The subsequent yield stress at zero suction

The preconsolidation stress of the subsequent yield surface

The yield stress at zero suction and temperature T

The yield stress at zero suction and reference temperature T 0

The yield stress at s and T

The pre-consolidation pressure with a reference temperature (T 0 ) and suction of 0

The value of subsequent yield stress at suction s and temperature T

The net stress at temperature T

The new yield stress of the new yield surface under zero suction after loading at the reference temperature ( T 0 )

The deviatoric stress

Matric suction

Represents the maximum suction value that the soil has ever suffered in history

Represents a non-zero suction value introduced to prevent the denominator from being zero, and the value range is 10 −2 –10 −5 Mpa

The saturated suction value

Bellia Z, Ghembaza MS, Belal T (2015) A thermo-hydro-mechanical model of unsaturated soils based on bounding surface plasticity. Computers and Geotechnics 69:58–69, DOI: https://doi.org/10.1016/j.compgeo.2015.04.020

Article   Google Scholar  

Deng ZQ, Chen JS, Wang JW, Liu XW (2020) Constitutive model and experimental study of uniform yield surface based on SFG model. Rock and Soil Mechanics 41(2):527–534, DOI: https://doi.org/10.16285/j.rsm.2019.0165

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The authors would like to acknowledge the financial supports he received from the National Natural Science Foundation of China (No.51268046), the National Natural Science Foundation of China (No.52169026).

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Liu, Xw., Wu, Zm. & Luo, Hl. Research and Verification of Unified Yield Surface SFG Model considering Temperature Influence. KSCE J Civ Eng (2024). https://doi.org/10.1007/s12205-024-1649-4

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• Published: 18 April 2024

Largest known madtsoiid snake from warm Eocene period of India suggests intercontinental Gondwana dispersal

• Debajit Datta   ORCID: orcid.org/0000-0001-6078-9830 1 &
• Sunil Bajpai   ORCID: orcid.org/0000-0002-2279-445X 1  

Scientific Reports volume  14 , Article number:  8054 ( 2024 ) Cite this article

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• Palaeontology

Here we report the discovery of fossils representing partial vertebral column of a giant madtsoiid snake from an early Middle Eocene (Lutetian, ~ 47 Ma) lignite-bearing succession in Kutch, western India. The estimated body length of ~ 11–15 m makes this new taxon ( Vasuki indicus gen et sp. nov.) the largest known madtsoiid snake, which thrived during a warm geological interval with average temperatures estimated at ~ 28 °C. Phylogenetically, Vasuki forms a distinct clade with the Indian Late Cretaceous taxon Madtsoia pisdurensis and the North African Late Eocene Gigantophis garstini . Biogeographic considerations, seen in conjunction with its inter-relationship with other Indian and North African madtsoiids, suggest that Vasuki represents a relic lineage that originated in India. Subsequent India-Asia collision at ~ 50 Ma led to intercontinental dispersal of this lineage from the subcontinent into North Africa through southern Eurasia.

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Introduction.

Madtsoiidae are an extinct clade of primarily Gondwanan terrestrial snakes with a temporal range spanning about 100 Myr from the Late Cretaceous–Late Pleistocene 1 , 2 , 3 . Their geographic range during the Late Cretaceous encompassed Madagascar, South America, India, Africa and the European archipelago 1 , 4 , 5 , 6 , 7 , 8 , 9 . The Cenozoic forms are restricted to North Africa, South America, the Indian subcontinent and Australia 2 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 . Madtsoiids display a broad spectrum of body-sizes and include some of the largest known terrestrial snakes that ever lived 2 , 7 , 9 . Although a speciose clade, most taxa are known exclusively from vertebrae, resulting in poorly constrained in-group relationships 2 , 8 , 16 . Additionally, the phylogenetic position of Madtsoiidae within Ophidia has remained contentious, as some studies recover it within Serpentes whereas others place it outside the crown group 3 , 9 , 17 , 18 , 19 , 20 . These phylogenetic uncertainties have hampered our understanding of madtsoiid biogeography and radiation events 2 , 8 .

In the Indian subcontinent, Late Cretaceous (Maastrichtian) madtsoiids are known from the Deccan volcanic province, including the large-sized Madtsoia pisdurensis from the Lameta Formation 6 , 8 . Among Tertiary madtsoiids, indeterminate forms are known from the early Paleocene Khadro Formation (Pakistan 16 ) and the early Eocene Cambay Shale (India 15 ). The latter also yielded the large madtsoiid Platyspondylophis 21 . The Eocene and Late Oligocene records include indeterminate taxa from Kutch and Ladakh, respectively 14 , 22 . Here we report the discovery of a giant madtsoiid snake, one of largest snakes ever reported, from an interval corresponding to a warm Middle Eocene period (~ 47 Ma) of India. Fossils were collected from an early Lutetian grey shale unit from Panandhro Lignite Mine, Kutch, Gujrat State, western India (Supplementary Note 1 , Fig.  1 ), and includes an excellently preserved, partial vertebral column. The discovery of a giant Eocene snake has important implications for madtsoiid biogeography in the context of Gondwanan inter-continental dispersal, and the evolution of large body-sizes possibly driven by high temperatures in the Middle Eocene tropical zones.

Geological map of Kutch Basin showing fossil locality ( a ); stratigraphic column at Panandhro Lignite Mine showing the position of madtsoiid snake-yielding horizon with age diagnostic dinoflagellate cyst assemblage and δ 13 C curve marking hyperthermal event ETM2 (modified after Agrawal et al. 23 ) ( b ); panoramic view of the fossil site ( c ). Map and stratigraphic column were drawn by D.D. using CorelDRAW 2019 (Version number: 21.0.0.593, URL link: http://www.corel.com/en/ ). ETM2 age estimate after Westerhold et al. 24 .

Systematic paleontology

Squamata Oppel, 1811

Ophidia Brongniart, 1800

Madtsoiidae (Hoffstetter 1961) McDowell, 1987

Vasuki indicus gen. et sp. nov.

Generic name after the well-known Hindu mythical serpent ‘Vāsuki’ around the neck of Lord Shiva; specific name is for the country of origin i.e., India.

IITR/VPL/SB 3102-1-21; a partial vertebral column representing the precloacal region (Figs. 2 , 3 ; Supplementary Table 1 ).

Anterior trunk vertebrae of Vasuki indicus . IITR/VPL/SB 3102-3, partial vertebra in anterior view ( a ); posterior view ( b ); left lateral view ( c ); dorsal view ( d ); ventral view ( e ). IITR/VPL/SB 3102-5, complete vertebra in anterior view ( f ); posterior view ( g ); left lateral view ( h ); dorsal view ( i ); ventral view ( j ). IITR/VPL/SB 3102-7I-II, partial vertebra in anterior view ( k ); posterior view; ( l ); left lateral view ( m ); dorsal view ( n ); ventral view ( o ). IITR/VPL/SB 3102-6, complete posterior anterior trunk vertebra in anterior view ( p ); posterior view ( q ); left lateral view ( r ); dorsal view ( s ); ventral view ( t ). Grey arrows indicate anterior direction. Red arrowheads and arrows indicate fossae on neural spinal base and endozygantral foramina, respectively. Roman numerals on figures ( m–o ) refer to individual vertebrae in articulated specimens where ‘I” is towards the anterior. White arrowhead and arrow indicate fossa medial to diapophysis and foramen on dorsal surface of neural arch. co cotyle, cn condyle, da diapophysis, hyp hypapophysis, izr interzygapophyseal ridge, msf median shaft, nc neural canal, nrl neural arch lamina, ns neural spine, pa parapophysis, pcof paracotylar foramen, pcofo paracotylar fossa, pcon paracotylar notch, po postzygapophysis, pr prezygapophysis, psl prespinal lamina, pzgf parazygantral foramen, pzgfo parazygantral fossa, scf subcentral foramen, scfo subcentral fossa, zg zygantrum, zs zygosphene. Scale bar represents 50 mm.

Precloacal vertebrae of Vasuki indicus . IITR/VPL/SB 3102-10I-II, complete posterior anterior trunk/mid-trunk vertebrae in anterior view ( a ); posterior view ( b ); right lateral view ( c ); dorsal view ( d ); ventral view ( e ). IITR/VPL/SB 3102-9I-II, partial mid-trunk vertebrae in anterior view ( f ); posterior view ( g ); left lateral (reversed) view ( h ); dorsal view ( i ); ventral view ( j ). IITR/VPL/SB 3102-4, nearly-complete mid-trunk vertebra in anterior view ( k ); posterior view; ( l ); left lateral (reversed) view ( m ); dorsal view ( n ); ventral view ( o ). IITR/VPL/SB 3102-8I-II, partial mid-trunk vertebrae in anterior view ( p ); posterior view ( q ); right lateral view ( r ); dorsal view ( s ); ventral view ( t ). IITR/VPL/SB 3102-11I-III, partial mid-trunk vertebrae in posterior view ( u ); right lateral view ( v ); dorsal view ( w ); ventral view ( x ). Grey arrows indicate anterior direction. Roman numerals on figures ( c–e,h–j,r–t,v–w ) refer to individual vertebrae in articulated specimens where ‘I” is towards the anterior. Pink and white arrows indicate fossae and foramen on lateral surface of centrum, respectively. Red arrow indicates endozygantral foramen. White arrowheads indicate paired protuberance on ventral median shaft. co cotyle, cn condyle, da diapophysis, hyp hypapophysis, izr interzygapophyseal ridge, msf median shaft, nc neural canal, nrl neural arch lamina, ns neural spine, pa parapophysis, pcof paracotylar foramen, pcofo paracotylar fossa, po post-zygapophysis, pr prezygapophysis, psl prespinal lamina, scf subcentral foramen, scfo subcentral fossa, zg zygantrum, zs zygosphene. Scale bar represents 50 mm.

Horizon and locality

Naredi Formation; Panandhro Lignite Mine, district Kutch, Gujarat state, western India.

Vasuki exhibits a unique combination of the following characters: presence of prominent paracotylar foramina (shared with Madtsoiidae); middle-sized cotyle (shared with Madtsoiidae); median prominence on ventral margin of centrum (shared with Madtsoiidae); prezygapophyseal process absent; high angle of synapophysis with horizontal in anterior view (avg. 71.5°); MTV diapophysis level with dorsoventral midpoint of neural canal (shared with Madtsoia madagascariensis , Madtsoia camposi , Wonambi barriei and Adinophis ); prezygapophyseal buttress succeeded posteriorly by elliptical fossa (shared with Madtsoia pisdurensis ); deep V-shaped embayment (shared with Gigantophis garstini and Madtsoia pisdurensis ); oval precloacal cotyle (shared with Gigantophis garstini and Madtsoia pisdurensis ); transversely wide vertebrae (shared with Gigantophis garstini and Madtsoia pisdurensis ); neural spine posteriorly canted (shared with Gigantophis garstini and Madtsoia pisdurensis ); broad hemal keel with posterior process (shared with Gigantophis garstini and Madtsoia pisdurensis ); strongly notched anterior zygosphenal margin; endozygantral foramen present (shared with Madtsoia madagascariensis , Powellophis and Gigantophis garstini ).

Autapomorphies: exceptionally large vertebrae [centrum length (cL): 37.5–62.7 mm and prezygapophyseal width (prW): 62.4–111.4 mm]; neural spine cross-section spade-shaped; poorly developed hemal keel which remains dorsal to the parapophyses; chisel-shaped posterior process of the hemal keel.

Description

The collection comprises 27 associated vertebrae which are mostly well-preserved and include a few in articulation (Figs.  2 A–T, 3 A–W). 22 out of the 27 specimens can be confidently assigned to the precloacal region based on the absence of hemapophyses, pleurapophyses and lymphapophyses, and are further constrained to a position anterior to the posterior trunk region as suggested by a greater mediolateral width of the neural arch compared to centrum length (sensu LaDuke 1 ; Rio and Mannion 2 ; Supplementary Tables 1 , 2 ; Supplementary Fig.  2 ). Such vertebral dimensions are usually found in large-bodied madtsoiids such as, Gigantophis 2 ; Yurlunggur 11 , Madtsoia 1 , 10 , 13 , and Wonambi 25 . Moreover, the closure of vertebral sutures suggests these specimens likely reached skeletal maturity, similar for instance to Madtsoia pisdurensis 8 .

Vasuki is characterized by exceptionally large vertebrae where centrum length (cL) and prezygapophyseal width (prW) range between 37.5–62.7 and 62.4–111.4 mm, respectively (Supplementary Table 2 ). We recognize this as an autapomorphy since these proportions eclipse all large-sized madtsoiids [ Madtsoia (cL = 18–25 mm; prW = 35–65 mm; LaDuke et al. 1 ), Gigantophis (cL = 28–41 mm; prW = 44–66 mm; Rio and Mannion 2 ), Platyspondylophis (cL = 18–21 mm; prW = 26–43 mm; Smith et al. 21 ) and Yurlunggur (cL = 15–22 mm; prW = 19–41 mm)]. Some caution, however, is warranted here because of uncertainties as to whether the largest size of these large-bodied madtsoiids has been captured, although, the same is true for Vasuki.

In overall form, the vertebrae of the new Indian taxon are massive (prW >> cL) and comprise a procoelous centrum. Anteriorly, the centrum preserves an anteroventrally inclined cotyle, whereas the posterior condyle is deflected posterodorsally resulting in considerable visibility of the condyle and cotyle in dorsal and ventral views, respectively (Fig.  2 C,E). In anterior view, the cotyle is strongly concave with its ventral margin recessed relative to the dorsal. The cotyle is mediolaterally wider than dorsoventrally high (Figs. 2 P, 3 A,F,K; IITR/VPL/SB 3102-4, coW/coH = 1.2; Supplementary Table 2 ) as in all madtsoiids [e.g., Gigantophis garstini 2 (NHMUK R8344, coW/coH = 1.2), Madtsoia madagascariensis (FMNH PR 2551, coW/coH = 1.24) Yurlunggur (NTM P8695-243, coW/coH = 1.22), and Wonambi (QMF23038, coW/coH = 1.4]. Laterally, the cotyle is bordered on each side by a well-developed and moderately deep paracotylar fossa (Figs. 2 K,P, 3 A,K). The dorsal and ventral margins of the fossa are prominent and defined by bony struts emanating from the dorsolateral and lateral cotylar margins, respectively. The lateral margin of the fossa, however, is flush with the surface. Furthermore, in some specimens the paracotylar fossa is divided into a shallower dorsal and deeper ventral sub-fossa by a weak secondary strut extending laterally from the dorsolateral margin of the cotyle. A tiny paracotylar foramen is present on the dorsal-most part of one or both paracotylar fossae, immediately lateral to the neural canal (Figs. 2 F,K,P, 3 A,K). While the presence of paracotylar fossae and foramina is a synapomorphy of Madtsoiidae 16 , 26 , the exact morphology of these features is variable across the clade. “ Gigantophis sp.” (CPAG-RANKT-V-1), Menarana nosymena and Adinophis fisaka (FMNH PR 2572) differ from Vasuki in the presence of paired paracotylar foramina on each side 1 , 16 , 27 . In Madtsoia and Eomadtsoia (MPEF-PV 2378) the foramina are deep and comparatively large, whereas in Yurlunggur these occur in clusters 7 , 8 , 10 , 11 , 13 . Eomadtsoia , however, shares with Vasuki the presence of prominent ventral rim of the paracotylar fossa 7 . In Gigantophis garstini the paracotylar fossa lacks a ventral margin and in Platyspondylophis the paracotylar foramen is absent altogether 2 , 21 .

The posterior condyle is transversely wider than high (IITR/VPL/SB 3102–4, cnW/cnH = 1.2; Supplementary Table 2 ) with the width progressively increasing from ATV (Fig.  2 B,G; cnW/cnH = 1.1) to MTV (Fig.  3 G, Q; cnW/cnH = 1.2–1.3). Similar proportions of the posterior condyle characterize most madtsoiids [e.g., Nidophis (LPB FGGUB v.547/3, ATV, cnW/cnH = 1.1; LPB FGGUB v.547/1, MTV, cnW/cnH = 1.2); Gigantophis garstini (NHMUK R8344, MTV, cnW/cnH = 1.2 Rio and Mannio 2 ); Madtsoia camposi (DGM 1310b, MTV, cnW/cnH = 1.3] (Fig.  3 G,I,Q). Furthermore, in posterior view, two small, distinct fossae are discernible on the lateral surface of the centrum immediately posterior to the left diapophysis (Fig.  3 G,I,Q). The fossae are vertically arranged, on top of each other, and separated by a prominent ridge. Whether these unilateral fossae represent an individual condition or a general feature cannot be currently ascertained and will require additional specimens of Vasuki .

The synapophysis is dorsoventrally high and comprises a distinct diapophysis and parapophysis (Figs.  2 M,R, 3 C,R) unlike in Gigantophis garstini , Madtsoia madagascariensis , and Madtsoia pisdurensis 1 , 2 , 8 . In anterior view, the orientation of the synapophysis changes from ventrolateral (Fig.  2 F,K) to somewhat laterally facing (Fig.  3 K,P,U) across the precloacal series. This change is marked by an increase in the synapophyseal angle (α), with the horizontal, from ATV (α = avg. 56.6°) to MTV (α = avg. 71.5°). A narrower synapophyseal angle was observed in most of the comparative madtsoiid taxa including Eomadtsoia [MPEF-PV 2378 (MTV), α = 45°], Gigantophis garstini [NHMUK R8344 (MTV) α = 48], Madtsoia madagascariensis [FMNH PR 2549 (ATV), α = 47°; FMNH PR 2551 (MTV), α = 56°], “ Gigantophis sp.” [CPAG-RANKT-V-1 (MTV), α = 56°], Madtsoia camposi [DGM 1310c (MTV), α = 57°], Wonambi [QMF23038 (MTV) α = 58°] and Madtsoia bai [AMNH 3155 (MTV), α = 62°]. In lateral view, the synapophysis is inclined at (β) 20°–27° from the vertical in Vasuki . This is similar to Wonambi [QMF23038, β = 25°], Nanowana [QMF19741, β =  ~ 25°], Madtsoia camposi [DGM 1310c, β = 26°] and Yurlunggur [P8695, β = 22°–26°]. In contrast, wider angles characterize Gigantophis garstini [NHMUK R8344, β = 30° 2 ], Platyspondylophis [β = 30°–35°], Madtsoia madagascariensis [FMNH PR 2549, β = 33°] and “ Gigantophis sp.” [CPAG-RANKT-V-1, β =  ~ 90°], whereas in Patagniophis [β = 7°–9°], Powellophis [PVL 4714–4, β = 18°] and Madtsoia pisdurensis [225/GSI/PAL/CR/10, β = 12°] the angles are narrower.

An arcuate paracotylar notch (sensu LaDuke et al. 1 ), between the ventral cotylar rim and the parapophysis, is consistently present in all specimens (Fig.  2 A,F). The parapophysis comprises a sub-rectangular facet, in lateral view, and extends below the ventral cotylar rim in ATV (Fig.  2 F,H,P,R). In MTV it lies dorsal to the ventral cotylar rim (Fig.  3 F,P) unlike Madtsoia pisdurensis and Gigantophis garstini where the parapophyseal base is ventral and in level with the ventral cotylar rim, respectively 2 , 8 . The diapophysis is bulbous and extends laterally beyond the prezygapophysis (Figs. 2 F,H, 3 P,R), contrary to Powellophis 3 , Patagoniophis australiensis 28 , Madtsoia pisdurensis 8 , Madtsoia madagascariensis 1 and Nidophis 9 . The dorsal margin of the diapophysis remains ventral to the dorsal cotylar margin in ATV (Fig.  2 A,F), but becomes level with the dorsoventral midpoint of the neural canal in MTV (Fig.  3 K,P). A similar disposition of the MTV diapophysis is observed in Madtsoia madagascariensis , Madtsoia camposi , Wonambi barriei and Adinophis 1 , 2 , 13 , 27 . The dorsal diapophyseal margin lies between the ventral margin of the neural canal and the dorsoventral midpoint of the cotyle in “ Gigantophis sp.” 16 , Gigantophis garstini 2 , Nidophis 9 , Yurlunggur 11 and Powellophis 3 . In Platyspondylophis the diapophysis extends beyond the ventral margin of the neural canal in all preserved precloacal vertebrae 21 .

The prezygapophyseal buttress is massive, lacks a prezygapophyseal process and bears an oblique, blunt ridge anteriorly (Fig.  2 F,K). In lateral view, the buttress is succeeded posteriorly by an elliptical fossa (Fig.  2 C,H,R). The fossa occurs immediately ventral to the interzygapophyseal ridge and medial to the diapophysis, similar to Madtsoia pisdurensis (Mohabey et al. 8 ). The prezygapophyseal facets are elliptical (5022–4, przL/przW = 1.3) and inclined ventromedially (prα = 20°–28°; Fig.  2 A,D,F,I). In dorsal view, these facets diverge at 45° from the sagittal plane, contrary to the transversely oriented facets in Madtsoia bai 10 , Madtsoia madagascariensis 1 , Platyspondylophis 21 , and Yurlunggur 11 . Strongly divergent prezygapophyses are also observed in Gigantophis garstini 2 (~ 70°) and Eomadtsoia 7 (60°–80°). The postzygapophyseal facets in Vasuki are also elliptical (IITR/VPL/SB 3102-8II, pozL/pozW = 1.2; Supplementary Table 2 ) and medioventrally oriented (poα = 12°–26°; Figs.  2 G,J, 3 B,E). The interzygapophyseal ridge is thick and posterodorsally directed, acting as a bridge between the pre- and postzygapophyses. A small lateral foramen is present ventral to the ridge (Fig.  3 L,Q) as in Powellophis 3 . In dorsal view the interzygapophyseal ridges are straight and differ from the arcuate ridges seen in most madtsoiids [e.g., Madtsoia , Gigantophis garstini , Wonambi , Yurlunggur and Platyspondylophis ] 2 , 8 , 10 , 11 , 13 , 18 , 21 , 28 .

The neural canal is reniform (Figs.  2 P,Q, 3 F,G) in cross-section and significantly wider than high (ncW/ncH = 3–3.6). It differs from the comparatively narrower and trilobate neural canal in Gigantophis garstini 2 (NHMUK R8344, ncW/ncH = 2.3), Platyspondylophis (WIF/A 2271, ncW/ncH = 2.1), Madtsoia (ncW/ncH = 1.3–2.3), Yurlunggur (NTM P8695-243, ncW/ncH = 2.3), “ Gigantophis sp.” (CPAG-RANKT-V-1, ncW/ncH = 1.8) and Powellophis (PVL 4714–4, ncW/ncH = 1.6), and the sub-elliptical canal in Wonambi (QMF23038, ncW/ncH = 1.3).

The zygosphene is trapezoidal and mediolaterally wider than high (zsW/zsH = 1.4–1.8; Fig.  2 A,K), as in Gigantophis garstini (NHMUK R8344, zsW/zsH = 2 2 ), Madtsoia bai (AMNH 3155, zsW/zsH = 1.8) and Madtsoia madagascariensis (FMNH PR 2551, zsW/zsH = 1.9). Transversely much wider zygosphenes characterize Nidophis (LPB FGGUB v.547/1, zsW/zsH = 5), Madtsoia camposi (DGM 1310a, zsW/zsH = 2.8), Eomadtsoia (MPEF-PV 2378, zsW/zsH = 2.6), Platyspondylophis (WIF/A 2269, zsW/zsH = 2.2) and Patagoniophis (QMF 19717, zsW/zsH = 5). In Vasuki , the zygosphene is wider than the cotyle, contrary to Gigantophis garstini , “ Gigantophis sp.”, Platyspondylophis and Madtsoia 1 , 8 , 10 , 13 , 16 , 21 . In anterior view, dorsal margin of the zygosphene is straight and the articular facets are steeply inclined (~ 40° form the vertical; Figs. 2 F,P, 3 A). These facets are oval in lateral view (IITR/VPL/SB 3102–6, zsfL/zsfW = 1.1). The anterior zygosphenal margin is markedly notched in dorsal view (zsα = 118°–128°; Figs. 2 I,N, 3 N), and differs from the non-notched zygosphene in Madtsoia pisdurensis 8 , Madtsoia camposi 13 , Eomadtsoia 7 and Platyspondylophis 21 . In “ Gigantophis sp.” (zsα = 145°) and Madtsoia madagascariensis (zsα = 145°–147°) the zygosphene is weakly notched.

The zygantrum is mediolaterally wider than high, with steeply inclined facets (50°–60° from the horizontal; Fig.  2 B,G,Q). The facets are elliptical in posterior view, but devoid of a median wall present in Gigantophis garstini 2 . An anteroventrally directed fossa is present at the base of each facet, and accommodates an endozygantral foramen (Figs. 2 G, 3 B). The latter is also present in Madtsoia madagascariensis 1 , Powellophis 3 and Gigantophis garstini 2 . In Vasuki , the zygantral roof above each facet is medio-dorsally convex and descends as sub-vertical ridges into the zygantrum (Fig.  2 Q) as in Madtsoia madagascariensis 1 . The roof is ventrally convex in Eomadtsoia and Madtsoia pisdurensis , and straight in Powellophis , Platyspondylophis , Yurlunggur and Gigantophis garstini 3 , 7 , 8 , 11 , 21 . A large, dorsolaterally oriented, elliptical parazygantral fossa flanks the zygantrum laterally on either side and bears a small parazygantral foramina (Fig.  2 B,G,Q).

The neural spine is dorsoventrally high (MTV, nsH/tvH = 0.21–0.29, Supplementary Table 2 ) and buttressed posteriorly by the neural arch laminae (Fig.  3 B–D,V,W). The latter extend anterodorsally from the dorsolateral margin of the postzygapophyses up to the dorsal spinal margin, resulting in a deep median embayment. In lateral view, the spine is steeply inclined posterodorsally (12°–19° from the vertical) with a concave anterior and a straight posterior margin. While a high neural spine characterizes most large madtsoiids [ Madtsoia camposi (DGM, 1310b, MTV, nsH/tvH = 0.22), Madtsoia madagascariensis (FMNH PR 2551, MTV, nsH/tvH = 0.33), Madtsoia bai (AMNH 3154, MTV, nsH/tvH = 0.22), Wonambi (QMF23038, MTV, nsH/tvH = 0.27)], it is more gently inclined in these large-sized taxa [e.g., Madtsoia madagascariensis (27°–33°), Wonambi (30°), Gigantophis garstini (30°)]. A convex anterior margin in Madtsoia madagascariensis as well as Powellophis and Nanowana further distinguishes them from Vasuki . Furthermore, the presence of a sharp postspinal lamina (sensu Tschopp 29 ) on the posterior spinal surface and a spade-shaped cross-section of the spine differentiates Vasuki from other madtsoiids (Figs.  2 D,S, 3 D). In dorsal view, the neural spine base is flanked on either side by a prominent fossa (Fig.  2 I,S), as in Madtsoia pisdurensis 8 and Madtsoia madagascariensis 1 . The fossae occur immediately posterior to the zygosphene and are bordered ventrally by weak, rounded bony struts emanating from the posterolateral zygosphenal margin. Ventral to these struts, a prominent foramen is present on the dorsal surface of the neural arch posterior to the zygosphene (Fig.  2 I), similar to Madtsoia madagascariensis 1 .

In ventral view, the centrum is triangular and widest across the parapophyses. Large paired subcentral fossae, more prominent in the anterior trunk vertebrae (ATV), occupy most of the ventral surface of the centrum (Figs.  2 J,O, 3 E,T). The fossae are bordered laterally by robust subcentral ridges that extend posteromedially from the parapophyses to the dorsoventral midpoint of the condyle. These ridges are straight to weakly convex in ventral view and differ from the concave ridges in Patagoniophis 28 and Madtsoia madagascariensis 1 . The subcentral fossae are separated by a transversely convex low hemal keel (Figs.  2 T, 3 E,O,T). The latter is broad, weakly raised and terminates anterior to the precondylar constriction. The hemal keel is not prominent, unlike the narrow/sharp keel in “ Gigantophis sp.”, Eomadtsoia , Nidophis , Nanowana and Powellophis 2 , 3 , 7 , 9 , 16 . In Vasuki , this keel remains dorsal to the ventral parapophyseal margin (Figs. 2 M,R, 3 M,R,V) unlike the hemal keel of other madtsoiids which descends below the parapophysis. Consequently, we identify the disposition of the hemal keel as an autapomorphy of Vasuki .

A small subcentral foramen is present on either side of the ventral shaft in Vasuki (Fig.  2 E,O,T), as in Madtsoia madagascariensis 1 , Madtsoia camposi 13 , Nidophis 9 , and Patagoniophis 28 . The hypapophysis is paddle-like with sharp lateral margins and extends up to the level of the ventral condylar rim in ATV (Fig.  2 G,H,J,L,M,O). The hypapophysis is directed posteroventrally unlike the ventrally directed hypapophysis in Madtsoia madagascariensis 1 and Patagoniophis 28 . Across the precloacals, the hypapophysis progressively reduces in prominence and is replaced by a chisel shaped structure with paired protuberances separated from the ventral condylar rim by a short, sharp ridge in the mid-trunk vertebrae (MTV; Fig.  3 J,O,T,X). This chisel shaped structure appears autapomorphic for Vasuki as it differs from the condition in other madtsoiids.

Phylogenetic analysis

The position of Vasuki within Madtsoiidae was tested in a modified version of the character-taxon matrix of Zaher et al. 30 (Analysis 1; see “ Methods ” section and Supplementary Note 2 ). 50 most parsimonious trees were recovered with a tree length of 1610, consistency index (CI) of 0.386 and retention index (RI) of 0.73. The resultant tree topologies are largely consistent with Zaher et al. 30 as Madtsoiidae was recovered as a distinct clade within crown Serpentes (Fig.  4 , Supplementary Fig.  3 ). Madtsoiidae, however, was poorly resolved and did not provide insights into the inter-relationship of Vasuki with the other members of the clade. The poor resolution is likely a reflection of the absence of cranial material in majority of madtsoiids and a function of the large matrix where very few vertebral characters could be scored for most madtsoiid taxa. We, therefore, ran a second analysis (Analysis 2) by removing all non-madtsoiid Serpentes and combining the cranial and vertebral characters of Zaher et al. 30 and Garberoglio et al. 3 , respectively (see “ Methods ” section and Supplementary Note 3 ). The latter dataset was used because as the study focused on madtsoiid ingroup relationships. Our analysis recovered only two most parsimonious trees with a tree length of 191, CI of 0.634 and RI of 0.62. Both trees (Fig.  5 , Supplementary Fig.  4 ) were mostly well resolved and the resultant topologies largely consistent with recent studies 2 , 3 , 7 on madtsoiid inter-relationships. Madtsoiidae shows size-based clustering with the small (< 2 m) and medium–large bodied (> 3 m) taxa recovered as separate clades (Fig.  5 ). Vasuki is nested within a distinct clade (Bremer support = 3) as a sister taxon to Indian Late Cretaceous Madtsoia pisdurensis  + North African Late Eocene Gigantophis garstini .

Phylogenetic position of Vasuki indicus gen. et sp. nov. IITR/VPL/SB 3102 in 50% majority-rule tree of Analysis 1. Clade comprising Vasuki indicus highlighted in pink. Numbers above and below nodes indicate the frequency a clade is represented in the most parsimonious trees and Bremer support values, respectively.

Phylogenetic position of Vasuki indicus gen. et sp. nov. IITR/VPL/SB 3102 in 50% majority-rule tree of Analysis 2. Clade comprising Vasuki indicus highlighted in pink. Numbers above and below nodes indicate the frequency a clade is represented in the most parsimonious trees and Bremer support values, respectively.

Estimation of body length

Quantitative estimates of total body length (TBL) of Vasuki were made based on two separate methods which have been used in recent years for size estimation of extinct large-bodied snakes (see “ Methods ” section and Supplementary Tables 3 – 5 ). In these methods TBL was regressed on the postzygapophyseal width (following Head et al. 31 ; Rio and Mannion 2 ) and the prezygapophyseal width (= trans-prezygapophyseal width; following McCartney et al. 32 , Garberoglio et al. 3 ), respectively. In the present study estimates were made from MTV (IITR/VPL/SB 3102-4, 3102-8I–II, 3102-11II–III), the largest specimens in the collection, following Rio and Mannion 2 , McCartney et al. 32 and Garberoglio et al. 3 . Both regression models were statistically significant (p < 0.05) and had a high explanatory power (r 2  = 0.83–0.96) which asserts their validity. The TBL estimates following Head et al. 31 ranges between 10.9 and 12.2 m (Fig.  6 A,B), whereas those following McCartney et al. 32 is between 14.5 and 15.2 m (Fig.  7 A). These estimates, however, should be treated with caution as the collection lacks posterior precloacal and cloacal vertebrae, and an understanding of the intracolumnar variation in madtsoiids is currently non-existent.

Regressions of vertebral metrics on total body length in extant boine taxa. Regression of postygapophyseal width on total body length in extant boine taxa from vertebrae 60% posteriorly along the vertebral column; p = 0.00000003, standard error =  ± 0.3 m ( a ). Regression of postygapophyseal width on total body length in extant boine taxa from vertebrae 65% posteriorly along the vertebral column; p = 0.00000001, standard error =  ± 0.2 m ( b ). Measurements of extant boine snakes taken from Head et al. 31 and plotted as black circles. Estimated body lengths of Vasuki indicus shown in red.

Regression of total body length on prezygapophyseal width in extant snakes. Measurements of extant snakes taken from McCartney et al. 32 and plotted as black circles. Estimated body lengths of Vasuki indicus shown in red. p = 0.000000000000003; standard error =  ± 0.09 m.

It is worth noting that the largest body-length estimates of Vasuki appear to exceed that of Titanoboa , even though the vertebral dimensions of the Indian taxon are slightly smaller than those of Titanoboa . We acknowledge that this observation may be a reflection of the different datasets used to formulate the predictive equations. However, we do not disregard the results based on the dataset of MacCartney et al. 32 , since the equations derived from the dataset of Head et al. 31 involve measurements of extant boine taxa that are taken from vertebrae 60–65% posteriorly along the column. Caution is warranted here because of the uncertainties surrounding the phylogenetic position of Madtsoiidae relative to crown snakes which make estimations based on a model depicting intracolumnar variation in vertebral morphology of a particular extant family/taxa tentative. Consequently, predictive regression equations following McCartney et al. 32 , which comprise vertebral data from an array of extant snakes, are also considered in our study.

Phylogenetic implications

The analyses presented here recovered a monophyletic Madtsoiidae with the clade placed within crown Serpentes in Analysis 1 (Fig.  4 , Supplementary Fig.  3 ). This is in accordance with most phylogenetic studies which assessed the relationship of snake total group within Squamata 30 , 33 , 34 , 35 . Furthermore, similar to Zaher et al. 30 , the tree topology in Analysis 1 recovered Sanajeh , Diniliysia , Najash stemward of crown Serpentes. Although the clade Madtsoiidae remains poorly resolved in Analysis 1, we found a combination of five synapomorphies supporting the placement of Vasuki within Madtsoiidae [centrum broad and subtriangular (ch 613); deep V-shaped embayment along posterior margin of neural arch (ch 614); presence of well-developed paracotylar foramina (ch 615); absence of prezygapophyseal accessory process (ch 616); presence of parazygantral foramina (ch 617)].

On the other hand, Analysis 2 gave insights into the ingroup relationships of Madtsoiidae (Fig.  5 , Supplementary Fig.  4 ). The resultant topologies are largely comparable with previous phylogenetic results 2 , 3 , 7 , 9 , as the taxa were found to resolve into two size-based clades (large vs small). While the possibility of size-related features driving such groupings cannot be ruled out, the recovery of small–medium sized taxa (e.g., Adinophis , Menarana , Powellophis ) within the large bodied clade suggests the presence of size-independent characters supporting these clades. A similar argument was also put forward by Garberoglio et al. 3 while discussing the occurrence of size-based clades within Madtsoiidae. However, none of the speciose genera (e.g., Madtsoia , Nanowana , Menarana ) included in this study formed monophyletic clades. The Bremer support for most internal nodes within Madtsoiidae remains low, although a few have comparatively higher support (Fig.  5 ). These results highlight the need for more rigorous sampling involving a better anatomical coverage of madtsoiids, leading to more robust phylogenetic relationships.

A unique combination of 7 synapomorphies nest Vasuki within Madtsoiidae [well-developed paracotylar foramina (ch 610); median prominence on ventral margin of centrum (ch 611); coW:dW between 0.5 and 0.3 (ch 634); lateral ridge on precloacal vertebrae below lateral foramen (ch 635); thick zygosphene (ch 645); moderately high neural spine (ch 648); lateral foramina present dorsal to subcentral ridges (ch 650)]. Furthermore, a combination of 6 unambiguous synapomorphies [posterior neural arch margin with deep V-shaped embayment (ch 614); oval precloacal cotyle (ch 615); transversely wide vertebrae (ch 629); hemal keel not sharp and narrow (ch 633); neural spine posteriorly canted (ch 652); presence of posterior process of hemal keel (ch 653)] support the placement of Vasuki with Gigantophis garstini and Madtsoia pisdurensis . Moreover, a single autapomorphy characterises Vasuki —chisel-shaped process of hemal keel (ch 654).

It is noteworthy that some of the synapomorphies mentioned above may be individually plesiomorphic characters, it is the unique combination of characters that justifies the recovery of Vasuki within Madtsoiidae. Previous studies (e.g., Head et al. 31 ; Mohabey et al. 8 ) have used character combinations to diagnose Madtsoiidae and other snake taxa.

Body length estimation and paleoecology

Our TBL estimations show that Vasuki was not only the largest madtsoiid (Table 1 ) but one of the largest snakes ever reported. Its vertebral dimensions are second only to the Paleocene Boinae Titanoboa (Head et al. 31 ). We attempted to infer the paleoecology of this large Indian madtsoiid from vertebral morphology since several previous studies on other extinct snakes (e.g., Palaeophis colossaeus , Powellophis and Madtsoia madagascarensis ) have highlighted the importance of vertebrae in paleoecological reconstructions 1 , 3 , 32 . The transversely wide vertebrae of Vasuki bear mainly laterally-directed synapophyses which would have been associated with laterally directed ribs, suggesting a broad and cylindrical body (see McCartney et al. 32 ). These features suggest a non-aquatic lifestyle for Vasuki as opposed to aquatic snakes which may possess high pterapophyses and have laterally compressed vertebrae with ventrally facing synapophyses, thereby placing the ribs beneath the vertebrae 3 , 32 , 36 . A high pterapophysis, however, is absent in many aquatic snakes and changes in the orientation of synapophyses from ventral to lateral across the vertebral column have been previously noted in aquatic snakes such as Simoliophis 37 . In hydrophiine sea snakes the vertebrae show true lateral compression only in the caudal region. Therefore, the possibility of an aquatic lifestyle for this giant Indian madtsoiid cannot be completely ruled out. An arboreal lifestyle is unlikely, judging from the large size of Vasuki and the fact that arboreal snakes tend to have elongated vertebrae with short zygapophyses 38 . A non-fossorial habitat is inferred here for Vasuki based on large body-size and non-depressed neural arch-spine complexes which would have placed the dorsal muscles (e.g., M. Semispinalis et spinalis, M. Interarticularis superior) away from the sagittal plane (sensu Auffenburg 39 ) 1 , 3 . This is further supported by the inferred presence of dorsoventrally thick M. multifidus , which originates from the anterodorsal neural spinal surface and inserts anteriorly onto the posterior margin of the neural arch laminae of the preceding vertebra. Gross similarity in vertebral morphology with extant large-bodied pythonids (e.g., Python and Malayopython ) 40 suggests a terrestrial/semi-aquatic paleohabitat for Vasuki . Corroborative evidence comes from the depositional environment of the Vasuki -yielding horizon, which was reconstructed as a back swamp marsh 23 , 41 , 42 , 43 , 44 , 45 , similar to the habitat of modern large pythonids.

Vasuki is envisaged as a slow-moving snake that possibly adopted a rectilinear locomotory mechanism as indicated by its large size, anteroposteriorly short and transversely wide vertebrae and absence of accessory prezygapophyseal processes 1 , 38 , 46 . A similar, anatomy-based inference was also drawn for the large Malagasy Madtsoia madagascariensis 1 , although rectilinear locomotion has also been documented in extant snakes with well-developed prezygapophyseal processes, such as vipers 47 . In spite of the uncertainties associated with the locomotory mechanism of Vasuki , it was perhaps too large to be an active forager and was more likely an ambush predator that would subdue its prey through constriction, similar to modern anacondas and large-bodied pythonids 1 , 42 , 48 .

The new Indian madtsoiid suggests a relatively warm climate (~ 28 °C) for the Middle Eocene (early Lutetian) paleogeographic position of India within the tropical zone 49 , 50 . This inference stems mainly from empirically derived dependence of poikilotherm body temperature on the ambient environmental temperature, which in turn controls the maximum body size 31 , 32 , 51 . Following Head et al. 31 , the mean annual paleotemperature (MAPT) for the Middle Eocene was estimated based on a relationship between the present mean annual temperature (MAT), TBL difference between Vasuki and reticulated python ( Malayopython reticulatus , the longest known extant snake) 42 and the mass-specific metabolic rate of pythons (see “ Methods ” section). The predicted MAPT falls between 27.2 and 28.6 °C, corresponding to the temperature range necessary for the survival of an 11–15 m snake, and suggests the Middle Eocene tropics were 0.7–2.1 °C (ΔT) warmer than at present (MAT = 26.5 °C 52 ). These estimates are largely comparable to those for the Palaeocene and Late Cretaceous based on the extinct Titanoboa (ΔT = 1.9–3.7 °C) and the frog Beelzebufo ampinga (ΔT = 2.1 °C), respectively 52 . Studies based on δ 18 O isotopic ratios from foraminifera and TEX86 index 53 , 54 , 55 , 56 have predicted high tropical sea surface temperatures (≥ 30 °C) during the Middle Eocene at ~ 47 Ma, whereas some estimates suggest tropical cooling for the early Middle and Late Eocene, but particularly during 45–34Ma 57 , 58 . The paleotemperature inferred here (< 30 °C) are lower than the afore-mentioned estimates (≥ 30 °C), but suggests that the Middle Eocene (early Lutetian, ~ 47 Ma) climate was warmer than at present.

A possible limitation of this study could be the use of a pythonid ( Malayopython reticulatus ) as the modern analog, especially since Pythonoidae and Madtsoiidae are phylogenetically distant. However, our choice of a modern analog is based on the inferred foraging mode and terrestrial/semi-aquatic paleohabitat of Vasuki , using anatomical data and the depositional environment of the fossiliferous horizon. The latter are similar to those of modern large pythonids which known to inhabit swamps, marshes and lowland forests 41 , 42 , 43 , 45 .

In India, Paleogene hyperthermal events, such as PETM and ETM2 are well documented from the Kutch and Cambay basins of western India based on δ 13 C negative excursions 23 , 59 , 60 , 61 . In comparison, studies on Paleogene paleotemperatures are scarce. Based on oxygen isotopic ratios, temperatures in excess of 30 °C were determined for the late Paleocene and early Eocene, whereas lower temperatures, ranging between 22 and 28 °C, were reported for the Middle–Late Eocene (~ 45–37 Ma) 62 , 63 . Our new estimates show that while the paleoclimate during the Middle Eocene (~ 47 Ma) became cooler compared to the Late Paleocene and early Eocene, it was still higher than at present. Further studies on Paleogene climates in the context of squamate speciation and extinction pattern are necessary in view of their suggested correlation with temperature patterns 64 , 65 , 66 .

Paleobiogeography

Madtsoiids were a major group of terrestrial snakes whose temporal range straddles the Cretaceous–Paleogene boundary. Fossil occurrences depict a skewed distribution of these snakes as most taxa are known from the Gondwanan landmasses, except Antarctica 1 , 2 (Figs.  8 , 9 ). The Laurasian record is extremely poor with madtsoiids known only from the Late Cretaceous (upper Campanian–Maastrichtian) of southern Europe 9 . The distributional pattern also shows the appearance of taxa on landmasses which were separated during the Late Cretaceous and Cenozoic but which share close phylogenetic relations indicating biogeographic links (sensu LaDuke et al. 1 ). This conundrum is aptly illustrated by the presence of Madtsoia in the Late Cretaceous (Maastrichtian) of Madagascar and India and the Early Paleogene of South America, and Menarana in the Maastrichtian of Madagascar and Spain 1 , 8 (Fig.  8 ). Previous studies put forward multiple scenarios for madtsoiid paleobiogeography including—a pan-Gondwanan distribution, albeit unsampled, during the Early Cretaceous followed by regional extinctions and/vicariance; presence of land bridges allowing dispersal between different Gondwanan landmasses and to Europe; sweepstakes dispersal between continents separated by oceanic barriers 1 , 8 , 9 . However, Rio and Mannion 2 argued in favour of an early pan-Gondwanan distribution and trans-Tethyan dispersals between Africa and Europe in the Late Cretaceous. The new Middle Eocene Indian madtsoiid further adds to the complexity of madtsoiid biogeography owing to its close phylogenetic ties with the Late Cretaceous Madtsoia pisdurensis from India and the Late Eocene North African Gigantophis garstini (Figs.  5 , 8 ).

Time-calibrated phylogenetic tree, based on the 50% majority-rule tree of Fig.  5 . Red star indicates position of Vasuki indicus . Clade for which biogeographic scenarios have been discussed are marked with colored nodes.

Palaeogeographic distribution of madtsoiids with taxa of different ages plotted together in a simplified Middle Eocene (50 Ma) map to show their global spatio-temporal occurences. Dashed-lines indicate possible dispersal routes between South America and Australia and the Indian subcontinent and North Africa. Palaeogeographic map after Scotese 43 and sourced from https://www.earthbyte.org/paleomap-paleoatlas-for-gplates/ [This work is licensed under the Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/ ]. Source of information on madtsoiid distribution from the Paleobiology database ( https://www.paleo-biodb.org/ ).

To assess the biogeographic significance of Vasuki we constructed a time-calibrated phylogenetic tree since this approach has been widely used in several previous studies for evaluating the paleobiogeographic significance of different vertebrate groups, including snakes and dinosaurs 2 , 67 , 68 , 69 . The rationale behind this approach is that phylogenetic relations are widely considered to be suggestive of biogeographic ties 1 , 70 , 71 , 72 . The phylogenetic tree used here is based on anatomically sparse data because most madtsoiid taxa are known exclusively from vertebrae and lack cranial material, resulting in weak support (Bremer support) for a majority of internal nodes within Madtsoiidae. For this reason, we restricted our biogeographic interpretations only to those nodes which had comparatively higher support (Bremer support ≥ 2; Fig.  8 ). Overall, the paleobiogeographic scenarios presented here should be treated with caution as future fossil discoveries may alter the phylogenetic position of some madtsoiid taxa and, in turn, the present biogeographic inferences.

Notwithstanding the above-mentioned limitations, the resultant tree in our study is consistent with the current consensus on madtsoiid origins as it suggests a Gondwanan origin reflecting the fact that all known early-diverging taxa are from erstwhile Gondwanan landmasses (Fig.  8 ). The tree topology argues for biotic exchanges between South America, Madagascar and Australia since the Malagasy Madtsoia madagascariensis (Late Cretaceous) and the South American Madtsoia bai (Eocene) are successive outgroups to the clade comprising the Neogene Yurlunggur and Wonambi from Australia. Paleogeographic reconstructions depict fragmentation of most major Gondwana landmasses by the early Cenomanian, with Indo-Madagascar separating from Australia–Antarctica by ~ 110 Ma 73 , 74 , 75 . However, previous studies suggested that land connections between South America and Australia facilitating faunal dispersal through Antarctica persisted till the early Eocene 1 , 75 (Fig.  9 ). On the other hand, the Malagasy–South American–Australian biotic link can likely be explained by the presence of madtsoiids or their most recent common ancestors in these continental blocks prior to their break-up. Recent studies on madtsoiid biogeography envisage an Early Cretaceous pan-Gondwana dispersal of these snakes, with ghost lineages from time-calibrated trees predicting an Aptian origin of Madtsoiidae 1 , 2 , 8 , 9 , 19 . The fossil record, however, is inconsistent with the hypothesized Early Cretaceous madtsoiid origins since their currently known earliest representatives are from the Coniacian–Santonian of Niger 1 , 2 , 9 , 76 , 77 . Future sampling from the pre-Maastrichtian horizons of Africa and Indo-Madagascar may help resolve this conundrum.

The Indian madtsoiids, namely Vasuki indicus , Madtsoia pisdurensis , and Platyspondylophis tadkeshwarensis , are resolved into two distinct sub-clades (Fig.  8 ). Platyspondylophis (Ypresian) and the Malagasy Adinophis fisaka (Maastrichtian) are recovered as sister-taxa, whereas Vasuki (early Lutetian) is the earliest-diverging member of a clade comprising Madtsoia pisdurensis (Maastrichtian) and the North African Gigantophis garstini (Priabonian). These phylogenetic relations suggest Late Cretaceous–Paleogene biotic exchanges between the Indian subcontinent, Madagascar and North Africa. Among the various competing hypotheses explaining such faunal links, Krause et al. 74 hypothesized connections ( stepping stones ) between the Indian subcontinent, Madagascar and Africa during the Late Cretaceous, which were possibly destroyed in subsequent tectonic events (e.g., subduction, hotspot related volcanism). The Oman-Kohistan-Ladakh arc (OKL) is another biogeographic pathway which is considered to have facilitated biotic interchanges between North Africa and India following the subcontinent’s collision with OKL at ~ 80 Ma 78 . While there is some support from paleomagnetic and radiometric data for the 80 Ma Indo–OKL collision 78 , subsequent studies based on detrital zircon ages and dating of post-collisional olasses have provided alternate explanations bearing on the sequence of accretion of the OKL with India/Asia 79 , 80 . These studies support OKL–Eurasia collision by ~ 100–80 Ma, with India colliding with Asia + OKL only during the Paleogene. This makes the possibility of Late Cretaceous Indo–African faunal exchange less likely 2 . More recent studies based on paleomagnetic data propose an initial collision between India and Kohistan-Ladakh arc at ~ 60–50 Ma followed by their final collision with Asia at ~ 45–50 Ma, with the arc being positioned at 8.3 ± 5.6°N at ~ 66–62 Ma 81 , 82 .

Among the scenarios discussed above we consider the following to be the most plausible explanation for the Indo-Madagascar-North African biotic links suggested by phylogenetic disposition of the Indian madtsoiids:

A sister taxa relationship between the Maastrichtian Malagasy Adinophis fisaka and Indian Platyspondylophis (Ypresian) suggests a dispersal event at or before Indo-Madagascar separation at ~ 88 Ma 83 . The direction of dispersal, however, remains uncertain as the available fossil evidence does not allow a critical evaluation of this hypothesis due to the poor sampling record of pre-Maastrichtian Malagasy and Indian deposits. However, recovery of Madtsoia from the Maastrichtian of both India and Madagascar 8 (Fig.  8 ) supports the prevalence of their biotic links, as also suggested by other groups including cordyliform lizards and the nigerophid Indophis 75 , 84 .

Post Indo-Madagascar separation at ~ 88 Ma, there was extended periods of isolation which ended with collision of the Indian subcontinent + Kohistan-Ladakh arc with Asia in the early Paleogene 50 , 81 , 82 resulting in biogeographic pathways with North Africa through southern Eurasia (Fig.  9 ).

Vasuki , Madtsoia pisdurensis and Gigantophis garstini form a distinct clade to the exclusion of others, with the earliest-diverging taxa from India (Fig.  8 ). This clade also shows close phylogenetic links between Late Cretaceous and Middle Eocene Indian taxa, suggesting a possible Indian origin for this clade. The placement of Gigantophis garstini within this clade indicates possible dispersal events from India to North Africa following India-Asia collision, consistent with the Late Eocene (Priabonian, 37–35 Ma 2 ) age of Gigantophis and recent paleobiogeographic reconstructions showing dispersal routes between India and North Africa via southern Eurasia following the collision 43 (Fig.  9 ). Whereas an African origin of Gigantophis garstini cannot be ruled out considering the recovery of madtsoiids from the Late Cretaceous deposits of that continent, the taxonomic and phylogenetic uncertainties offer little support for this hypothesis. However, Rio and Mannion’s 2 alternative explanation that an Early Cretaceous pan-Gondwanan dispersal and long ghost lineages may have led to close phylogenetic relations between Gigantophis garstini and the Indian madtsoiids, though potentially valid, is currently weakly supported because of poor sampling.

To summarize, we identify a lineage of exceptionally large-bodied madtsoiids (represented by the largest known madtsoiids, Vasuki and Gigantophis garstini ) which originated in the Indian subcontinent and subsequently spread to Africa via southern Eurasia during the Eocene. The discovery of Vasuki , and the sparse anatomical coverage of known madtsoiids highlight the need for rigorous sampling of Late Cretaceous and Paleogene Gondwanan deposits. Recovery of additional material and new taxa (including large-sized forms) may provide further insights into madtsoiid systematics and biogeography.

Osteological description

The osteological description of the skeletal specimens was carried out following the nomenclature of LaDuke et al. 1 , Rio and Mannion 2 and Mohabey et al. 8 . Different parameters of the fossil specimens were measured (Supplementary Fig.  2 ) using Mitutoyo digital callipers with a precision of 0.01 mm. Explanatory line drawings are used wherever necessary. The terminology for vertebral laminae and fossae follows Rio and Mannion 2 and Tschopp 29 .

The phylogenetic affinity of Vasuki was assessed in two separate analyses (Analysis 1 and 2). In Analysis 1 (Supplementary Dataset 1 ) the character-taxon matrix of Zaher et al. 30 was used. All non-Pan-Serpentes toxicoferans were removed except for Varanus exanthematicus which was used as the outgroup. 15 madtsoiid taxa, including Vasuki , were added. The character-taxon matrix included 72 taxa and 785 characters. The phylogenetic analysis was performed using TNT version 1.6 85 where the software memory was set to retain 10,000 trees and a display buffer of 10 Mb. The Traditional Search option was used to analyse the dataset. The constraints for the analysis included 50 replications of Wagner trees, in which the swapping algorithm was bisection reconnection with 10 trees saved per replication. To determine the robustness of the nodes, Bremer support values were calculated using the script bremer.run in which only trees suboptimal by 20 steps were retained.

In Analysis 2 (Supplementary Dataset 2 ) all non-madtsoiid Serpentes were removed except for the basal ophidians Najash and Sanajeh . The latter taxon was used as the outgroup. The dataset combined the cranial and vertebral characters of Zaher et al. 30 and Garberoglio et al. 3 , respectively. 3 additional madtsoiid taxa were included. The character-taxon matrix included 22 taxa and 656 characters. The analysis was performed using TNT version 1.6 85 following the software settings and search parameters of Analysis 1. The script bremer.run was used to calculate Bremer support values in which only trees suboptimal by 20 steps were retained.

Time-calibrated tree

This was constructed by plotting the temporal ranges of the snake taxa onto the majority rule tree of Analysis 2 against a numerically calibrated geological time-scale. The temporal ranges of the taxa used in this study have been obtained from the Paleobiology Database ( https://www.paleobiodb.org/ ), Rio and Mannion 2 , and Garberoglio et al. 3 .

Body length estimation

The body-length estimates of Vasuki were based on the datasets of Head et al. 31 and McCartney et al. 32 . The dataset of Head et al. 31 comprises measurements of trans-postzygapophyseal width (poW) and TBL of 21 extant boine taxa, whereas that of McCartney et al. 32 include measurements of trans-prezygapophyseal width and total body length of 21 extant snakes.

The following predictive regression equations were formulated after

Head et al. 31 :

where postzygapophyseal width (x) is equated with the total body length (y). The dataset was from vertebrae 60% posteriorly along the vertebral column, and was not log transformed as the measured parameters were approximately normally distributed (sensu Head et al. 31 ).

where postzygapophyseal width (x) is equated with the total body length (y). The dataset was from vertebrae 65% posteriorly along the vertebral column, and was not log transformed as the measured parameters were approximately normally distributed (sensu Head et al. 31 ).

McCartney et al. 32 and Garberoglio et al. 3 :

where trans-prezygapophyseal width (x) is equated with the total body length (y). Log transformed values of the measured parameters were used to normalize the dataset.

In previous studies, body lengths have been estimated for extinct snakes, which are part of extant clades, using maximum likelihood methods 31 , 32 . Head et al. 31 developed a model depicting intracolumnar variation of vertebral morphology in extant boines to assign vertebral specimens of the giant extinct boid Titanoboa to their most likely position in the vertebral column. Based on vertebral landmarks, the specimens of Titanoboa were matched to a position 60–65% posteriorly along the column (MTV, sensu Rio and Mannion 2 ), and size estimates were obtained by regressing TBL on poW based on vertebrae of extant boines from those positions. However, such models showing intracolumnar variation in madtsoiids are currently non-existent as very few of these snakes are known from complete/nearly complete vertebral column 2 . Size estimates of Vasuki were calculated in this study using MTV following Rio and Mannion 2 , although, these estimates should be considered tentative as the specimens of Vasuki cannot be assigned to the same position as the boine vertebrae used to formulate the equations. Also, there may be differences in the relationship between poW and TBL between extant boines and Vasuki . Furthermore, uncertainties associated with the phylogenetic position of Madtsoiidae relative to crown snakes, preclude formulation of models showing intracolumnar variation in vertebral morphology based on any extant clade. Consequently, predictive regression equations, based on data from an array of extant snakes from McCartney et al. 32 , were used to determine the body length of the new Indian taxon and therefore, the estimated lengths, though reasonable, should also be treated with caution.

Estimation of paleotemperature

Paleotemperature estimates were obtained using the following equation provided in Head et al. 31 :

where MAPT is the mean annual paleotemperature; MAT is the present mean annual temperature (26.5 °C 52 ); TBL M  = 10.05 m is the maximum total body length of Malayopython reticulatus 41 ; TBL V is the maximum estimated body length of Vasuki (15.2 m); Q 10 (mass specific metabolic rate of pythonids) = 2.6 86 ; α (metabolic scaling component) = 0.17 52 , 87 .

Since Madtsoiidae are an extinct clade, the body length of Malayopython reticulatus (Serpentes, Pythonidae) was used in the study as it is the longest known extant snake 42 . The choice of Malayopython as the modern analog is based on the similarity in gross vertebral morphology and, inferred mode of life and habitat between Vasuki and extant large-bodied pythonids 40 , 41 , 42 , 43 , 45 . However, in the absence of extant representatives of madtsoiids or their close relatives, the estimated paleotemperature values should be treated with caution.

Data availability

All data associated with the manuscript are provided in the Supplementary File.

Code availability

Nomenclatural acts. This published work and the nomenclatural acts it contains have been registered in Zoo- Bank, the proposed online registration system for the International Code of Zoological Nomenclature (ICZN). The LSIDs for this publication are urn:lsid:zoobank.org:act: 2F44E9BE-AE99-45E8-A132-D36A935D3B36 ( Vasuki ) and urn:lsid:zoobank.org:act: 0DD3FB9F-A500-4FFE-842C-EFE51EC76E4D ( V. indicus ).

Abbreviations

American Museum of Natural History, New York

Centre of Pure and Applied Geology, University of Sindh, Pakistan

Departamento Nacional de Produção Mineral, Rio de Janeiro, Brazil

The Field Museum, Chicago, USA

Vertebrate Paleontology Laboratory, Indian Institute of Technology Roorkee, Roorkee, India

Laboratory of Paleontology, Faculty of Geology and Geophysics, University of Bucharest, Bucharest, Romania

Vertebrate Paleontological collection, MuseoPaleontológico Egidio Feruglio, Trelew, Chubut Province, Argentina

Northern Territory Museum, Australia

The Natural History Museum, London, U.K.

Queensland Museum, Brisbane, Australia

Vertebrate Paleontological Collection of the Instituto Miguel Lillo, San Miguel de Tucumán, Argentina

Wadia Institute of Himalayan Geology, Dehradun, India

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Acknowledgements

The authors acknowledge with thanks the helpful comments, suggestions and a constructive critique of the manuscript by the reviewers and Editor, Scientific Reports. Authors also thank Ritu Sharma, Debasis Das, Vivesh Vir Kapur, N. Saravanan, Lisa Cooper, Lauren Stevens and Hans Thewissen for help during field work and, Aatreyee Saha, Abhay Rautela and Poonam Verma for help and discussions. The Science and Engineering Research Board (SERB) (Grant no. PDF/2021/00468 as National Post-doctoral Fellowship to DD) and the Department of Science and Technology (Project no. SR/S4/ES-222/2006 to SB), Government of India are acknowledged for financial support. DD would like to acknowledge IIT Roorkee for providing infrastructural facilities. SB would like to acknowledge support obtained from IIT Roorkee as part of his Institute Chair Professorship.

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S.B. and D.D. conceived the problem. S.B. collected the fossils. D.D. and S.B. analysed and interpreted the data and wrote the manuscript. S.B. and D.D. were involved in further revisions.

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Datta, D., Bajpai, S. Largest known madtsoiid snake from warm Eocene period of India suggests intercontinental Gondwana dispersal. Sci Rep 14 , 8054 (2024). https://doi.org/10.1038/s41598-024-58377-0

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Received : 18 October 2023

Accepted : 28 March 2024

Published : 18 April 2024

DOI : https://doi.org/10.1038/s41598-024-58377-0

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