Phylogenetic analysis of a new morphological dataset elucidates the evolutionary history of Crocodylia and resolves the long-standing gharial problem
File(s)
Published version
Author(s)
Rio, Jonathan
Mannion, Philip
Type
Journal Article
Abstract
First appearing in the latest Cretaceous, Crocodylia is a clade of mostly semi-aquatic, predatory reptiles, defined by the last common ancestor of extant alligators, caimans, crocodiles and gharials. Despite large strides in resolving extant and fossil crocodylian interrelationships over the last three decades, several outstanding problems persist in crocodylian systematics. Most notably, there has been persistent discordance between morphological and molecular datasets surrounding the affinities of the extant gharials, Gavialis gangeticus and Tomistoma schlegelii. Whereas molecular data consistently support asister relationship between the extant gharials, which appear to be more closely related to crocodylids than to alligatorids, morphological data indicate that Gavialisis the sister taxon to all other extant crocodylians. Here we present a new morphological dataset for Crocodylia, based on a critical re-appraisal of published crocodylian character data matrices and extensive first-hand observations of a global sample of crocodylians. This comprises the most taxonomically comprehensive crocodylian dataset to date (144 OTUs scored for 330 characters) and includes a new, illustrated character list with modifications to the construction and scoring of characters, and 46 novel characters. Under a maximum parsimony framework, our analyses recover Gavialisas more closely related to Tomistomathan to other extant crocodylians for the first time based on morphology alone. This result is recovered regardless of the weighting strategy and treatment of quantitative characters. However, analyses using continuous characters and extended implied weighting (with a high k value) produced optimal topologies overall. Resolution of the gharial problem reveals that: (1) several gavialoids lack plesiomorphic features that formerly drew them towards the stem of Crocodylia, and (2) more widespread similarities occur between species traditionally divided into tomistomines and gavialoids, with these interpreted here as homology rather than homoplasy. There remains significant temporal incongruence regarding the divergence timing of the extant gharials, indicating that several putative gavialids (‘thoracosaurs’) are incorrectly placed and require future re-appraisal. New alligatoroid interrelationships include: (1) support for a North American origin of Caimaninae in the latest Cretaceous; (2) the recovery of the early Paleogene South American taxon Eocaimanas a ‘basal’ alligatoroid; and (3) the paraphyly of the Cenozoic European taxon Diplocynodon. Among crocodyloids, notable results include modifications to the taxonomic content of Mekosuchinae, including biogeographic affinities of this clade with latest Cretaceous–early Paleogene Asian crocodyloids. In light of our new results, we provide a comprehensive review of the evolutionary and biogeographic history of Crocodylia, which included multiple instances of trans-oceanic and continental dispersal.
Date Issued
2021-09-06
Date Acceptance
2020-12-16
Citation
PeerJ, 2021, 9
ISSN
2167-8359
Publisher
PeerJ Inc.
Journal / Book Title
PeerJ
Volume
9
Copyright Statement
© 2021 Rio and Mannion. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ) and either DOI or URL of the article must be cited.
License URL
Subjects
06 Biological Sciences
11 Medical and Health Sciences
Publication Status
Published
Article Number
e12094
Date Publish Online
2021-09-06