Convergent Evolution in Aquatic Tetrapods: Insights from an Exceptional Fossil Mosasaur
Johan Lindgren1*, Michael W. Caldwell2,3, Takuya Konishi2¤, Luis M. Chiappe4
1 Department of Earth and Ecosystem Sciences, Lund University, Lund, Sweden, 2 Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada, 3 Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada, 4 The Dinosaur Institute, Natural History Museum of Los Angeles County, Los Angeles, California, United States of America
Abstract
Mosasaurs (family Mosasauridae) are a diverse group of secondarily aquatic lizards that radiated into marine environments during the Late Cretaceous (98–65 million years ago). For the most part, they have been considered to be simple anguilliform swimmers – i.e., their propulsive force was generated by means of lateral undulations incorporating the greater part of the body – with unremarkable, dorsoventrally narrow tails and long, lizard-like bodies. Convergence with the specialized fusiform body shape and inferred carangiform locomotory style (in which only a portion of the posterior body participates in the thrust-producing flexure) of ichthyosaurs and metriorhynchid crocodyliform reptiles, along with cetaceans, has so far only been recognized in Plotosaurus, the most highly derived member of the Mosasauridae. Here we report on an exceptionally complete specimen (LACM 128319) of the moderately derived genus Platecarpus that preserves soft tissues and anatomical details (e.g., large portions of integument, a partial body outline, putative skin color markings, a downturned tail, branching bronchial tubes, and probable visceral traces) to an extent that has never been seen previously in any mosasaur. Our study demonstrates that a streamlined body plan and crescent-shaped caudal fin were already well established in Platecarpus, a taxon that preceded Plotosaurus by 20 million years. These new data expand our understanding of convergent evolution among marine reptiles, and provide insights into their evolution's tempo and mode.
Citation: Lindgren J, Caldwell MW, Konishi T, Chiappe LM (2010) Convergent Evolution in Aquatic Tetrapods: Insights from an Exceptional Fossil Mosasaur. PLoS ONE 5(8): e11998. doi:10.1371/journal.pone.0011998
Editor: Andrew Allen Farke, Raymond M. Alf Museum of Paleontology, United States of America
Received: March 19, 2010; Accepted: July 12, 2010; Published: August 9, 2010
Copyright: © 2010 Lindgren et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This research was supported by the Swedish Research Council, the Crafoord Foundation, the Royal Swedish Academy of Sciences, the Natural Sciences and Engineering Research Council of Canada, the University of Alberta, Faculty of Science, Chair's Research Allowance, Alberta Ingenuity Fund (PhD Student Scholarship), and the Dinosaur Institute of the Natural History Museum of Los Angeles County. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
* E-mail: johan.lindgren@geol.lu.se
¤ Current address: Royal Tyrrell Museum of Palaeontology, Drumheller, Alberta, Canada
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