Dental News - Ancient amphibians had mouthful of teeth, research shows

Dental Tribune International

Fri. 26. January 2018

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TORONTO, Canada: The idea of being bitten by a nearly toothless modern frog or salamander sounds laughable. However, their ancient ancestors had a full array of teeth, large fangs and thousands of tiny hooklike structures called denticles on the roofs of their mouths that would snare prey, according to new research by paleontologists at the University of Toronto Mississauga (UTM).

In the study, paleontology professor Robert Reisz and his research team at UTM explained that 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 researchers believe that the tooth-bearing plates were ideally suited for holding on to prey, such as insects or smaller tetrapods (four-limbed vertebrates), and may have facilitated a method of swallowing food via retraction of the eyeballs into the mouth, as some amphibians do today.

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. However, in one group of tetrapods, 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 with. Since these toothy plates were suspended in soft tissue, they were often lost or scattered during fossilization.

Denticles are significantly smaller than the teeth around the margin of the mouth—to the order of dozens to several hundred microns in length. “They are actually true teeth, rather than just protrusions in the mouths of these tetrapods,” explained Reisz. “Denticles have all of the features of the large teeth that are found on the margin of the mouth. In examining tetrapod specimens dating back (approximately) 289 million years, 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,” he continued.

Reisz and his graduate students suggested that the next big question relates to evolutionary changes regarding 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?

The study, titled “Histological characterization of denticulate palatal plates in an Early Permian dissorophoid,” was published online in PeerJ, an open-access journal, on Aug. 22, 2017.

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