Crocodiles lived in water since Jurassic age: Fukushima Museum-led team finds from fossil analysis

Photo: Junki Yoshida (right) announces the outcome of research that zeroed in on the origin of aquatic adaptation by the crocodilian family.

A team of researchers led by Junki Yoshida, a 30-year-old curator at the Fukushima Museum in the Fukushima Prefecture city of Aizuwakamatsu, has found that ancestors of the crocodile may have adapted to living in water about 155 million years ago (the late Jurassic age) when dinosaurs were in the prime of their prosperity. Previously, it was not known when the crocodile began its semi-aquatic lifestyle. The team shed light on the matter by probing into the reptile's breathing functions. The discovery was published in the British science journal Royal Society Open Science on Dec. 8. Crocodiles belong to the reptile species that can live mainly on land. When did they begin living in water? In the anatomy of a fossil of the family Goniopholididae, which is a basal crocodilian group, the researchers used a unique study method in which they analyzed the fossil and compared the movements of its throat with those of modern-day crocodiles, succeeding in "delving into the mystery" of one aspect of the animal's evolution. "We were able to achieve the results from an innovative point of observation," Yoshida told reporters. "Going forward, we would like to continue working on the evolution process that is full of mystery." The fossil, unearthed in 1993 in the U.S. state of Wyoming, was named "Amphicotylus milesi" after its founder. It is believed that the reptile was about 3 meters long. The fossil was in good shape, making the discovery of its "hyoid bone" -- a rare finding. Yoshida began studying the fossil in the summer of 2017 when he was a Hokkaido University graduate school student. His comparisons of the fossil's features with those of fossils of other members of the family Goniopholididae led him to identify it as a new species. From the hyoid bone discovered, he focused his attention on the throat structure and breathing mechanism. Today's crocodiles have "gular valves" that prevent water from flowing into the body through the throat. This helps enable them to continue breathing for long hours through its above-water nostrils while the body and much of the head are underwater. And they are able to shut their throats off from the mouth while continuing to breathe, allowing them to tackle prey still in water. Yoshida discovered from his observations of modern crocodiles that it is possible to move the valve with the use of the musculature covering the hyoid bone. He considered that the newly found species, which has a similarly shaped hyoid bone, moved the valve in the same way, thus associating its aquatic adaptation with the palatal and hyoid morphologies. The research paper of Yoshida's team was completed in cooperation with five outside researchers -- at Hokkaido University's Graduate School of Science, Hokkaido University Museum, Carleton University of Canada, and Gunma Museum of Natural History. Geological strata dating back to the Jurassic age exist across Japan, including Fukushima, and Yoshida is eager to look for a similar discovery in the country. "Hopefully, we will make progress in the studies on domestic evolution as well," he said. The Fukushima Museum is scheduled to exhibit the fossil of the new species from 2022 onward together with other fossils uncovered in Fukushima. ==Kyodo