Carleton Earth Sciences professor, Dr. Michael J. Ryan, has discovered a new ancient crocodile relative that reveals how crocodiles evolved to hunt prey while still breathing underwater. The discovery has been published in Royal Society Open Science.

New Evolutionary Insights

The 155-million-year-old relative, Amphicotylus milesi, was discovered in Wyoming, USA is a new species and the best-preserved fossil known of a goniopholidid, a close relative of modern crocodilians.

With an estimated length of 2.3 m (7.6 ft) and weighing up to 227 kg (500 Ib), the freshwater species inhabited the margins of rivers and shallow lakes where it fed on fish or waited to ambush small dinosaurs.

Life reconstruction of new goniopholidid by Takashi Oda.

Amphicotylus has a backward, value-like extension of the air passage leading from the nostril to the back of the throat and a short and curved tongue bone (hyoid) similar to modern crocodiles. By keeping their external nostrils above the water surface, these crocodilian ancestors could hold its breath underwater while holding prey in its mouth by closing this valve, just as modern crocodilians do.

Amphicotylus gives us a unique window back in time to the evolution of one of the key features that made crocodiles and their relatives one of the Earth’s most successful group of land animals,” co-author Dr. Ryan said. “It was features such as this that may have helped crocodiles survive the asteroid impact that wiped out all of the non-avian (birds) dinosaurs 66 million years ago at the end of the Cretaceous.”

A ‘Jurassic Park’ Landscape

Amphicotylus was discovered in 1993 in Wyoming in the Upper Jurassic Morrison Formation by Western Paleontological Laboratories, Inc., at a locality not far from the famous Bone Cabin Quarry. Amphicotylus was collected from a quarry that also produced the skeleton of the large sauropod, Camarasaurus, a cousin of the well-known Brontosaurus.

Amphicotylus milesi’s skeleton. Image credit: Gunma Museum of Natural History

A favourite prey may have been juvenile Camarasaurus that Amphicotylus could have snatched from the water’s edge when they came to drink. Amphicotylus would have shared its ‘Jurassic Park’ landscape with dinosaurs such as the large sauropod, Diplodocus, the plated herbivore, Stegosaurus, and the apex predator of its day, Allosaurus.

Amphicotylus milesi is named in honour of Clifford Miles for his contribution to the excavation of the specimen.

Reference: Junki Yoshida, Atsushi Hori, Yoshitsugu Kobayashi, Michael J. Ryan, Yuji Takakuwa, and Yoshikazu Hasegawa. 2021. A new goniopholidid from the Upper Jurassic Morrison Formation, USA: novel insight 2 into aquatic adaptation toward modern crocodylians. Royal Society Open Science.

Wednesday, December 8, 2021 in ,
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