If you were asked to imagine a vicious predator from 289 million years ago, you likely would not imagine a frog. However, UTM paleontologist Robert Reisz and his graduate students, Bryan Gee and Yara Haridy, recently discovered a fossil that suggests that the ancestor to frogs may have been a force to be reckoned with.
The team discovered fossils of palatal plates belonging to a group of organisms called ‘dissorophoids,’ an ancestral group of modern amphibians. On these plates were hundreds to thousands of miniscule fang-like structures. The researchers detected evidence of tooth components on the fossils, including a pulp cavity, dentine, and enamel, which confirmed that the structures were indeed teeth.
These toothed plates would have been attached to a flexible palate on the roof of the amphibian’s mouth, allowing these ancient predators to capture and consume large prey. This is in stark contrast to the diet of amphibians today, which, although still carnivorous, consists of invertebrate prey such as insects.
This flexible palate is still present in modern amphibians — in fact, it is a defining characteristic of the group. The teeth, however, are nowhere to be found. Many modern amphibians do not possess any type of true teeth, let alone hooked palatal ones. Species that do possess true teeth are severely reduced in size. This then begs the question: why did amphibians lose their teeth?
The question is difficult to answer. “We don’t even know when they lost that trait,” Haridy told The Varsity.
“These platelets are found in all extinct amphibians… that suggests some sort of phylogenetic signal [for these teeth],” said Gee. Haridy explained that it would have likely taken some sort of genetic mechanism for these organisms to lose all their teeth.
Gee said that most research in paleontology often leads to more questions. Even if the researchers can pinpoint how, when, or why amphibians lost their teeth, another question would arise: how did amphibians remain so successful despite losing such a major component of their feeding apparatus?
“Amphibians are the longest-lived group of tetrapods. They beat reptiles, birds, mammals, [and] dinosaurs. [They] survived [multiple] mass extinctions that wiped out quite a lot of other animals,” said Gee.
While some questions remain unanswered, the implications of the discovery are crystal clear.
“This story is interesting from… the dental diversity side. So, how many different ways can we make a tooth with just one genetic module,” said Haridy, whose research focuses on dental histology. “A lot of amphibians are [model] organisms now. [When] you’re fiddling around with their genomics… it’s really important to understand the background features that they have… [and] probably still carry in their genes.”
The discovery also has conservation implications. “Amphibians are the most at-risk group of vertebrates on the planet,” said Gee. “If we can get a better idea of the diversity of physiology and morphology that we see in the fossil record… that [gives us] ideas of evolutionary rates and how quickly amphibians can adapt.”