Ancient Primitive Amphibians Had Mouthful of Teeth

Temnospondyls — a diverse group of extinct small-to-giant amphibians that flourished worldwide during the Carboniferous, Permian, and Triassic periods — had a full array of teeth, large fangs and thousands of tiny hook-like structures called denticles on the roofs of their mouths, according to new research published in the journal PeerJ.

“Denticles are significantly smaller than the teeth around the margin of the mouth — on the order of dozens to a couple hundred microns in length,” said University of Toronto Mississauga Professor Robert Reisz, senior author of the study.

“They have all of the features of the large teeth that are found on the margin of the mouth.”

In many vertebrates, ranging from fish to early synapsids (ancestors of mammals), denticles are commonly found in dense concentrations on the bones of the hard palate (roof of the mouth).

However, in temnospondyls — which are thought to be the ancestors of modern amphibians — these denticles were also found on small, bony plates that filled the large soft part of the palate. The entire roof of the mouth was covered with literally thousands of these tiny teeth that they used to grab prey.

“In examining temnospondyl specimens dating back approximately 289 million years (Permian period), we discovered that the denticles display essentially all of the main features that are considered to define teeth, including enamel and dentine, pulp cavity and peridontia,” Professor Reisz said.

He and his colleagues — Bryan Gee and Yara Haridy, graduate students at the University of Toronto Mississauga — analyzed specimens unearthed from the Dolese Brothers Limestone Quarry near Richards Spur, Oklahoma.

They extracted and isolated the denticle-bearing plates, created thin section slides and examined them under the microscope.

“The presence of such an extensive field of teeth provides clues to how the intriguing feeding mechanism seen in modern amphibians was also likely used by their ancient ancestors,” the paleontologists said.

“We believe that the tooth-bearing plates were ideally suited for holding on to prey, such as insects or smaller tetrapods, may have facilitated a method of swallowing prey items via retraction of the eyeballs into the mouth, as some amphibians do today.”

“The next big question relates to evolutionary changes to the overall abundance of teeth: if these ancient amphibians had an astonishing number of teeth, why have most modern amphibians reduced or entirely lost their teeth?”

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B.M. Gee et al. 2017. Histological characterization of denticulate palatal plates in an Early Permian dissorophoid. PeerJ 5: e3727; doi: 10.7717/peerj.3727

Source: www.sci-news.com