Oldest frog relative, identified by paleontologists.
Tiny fossils unearthed in Arizona’s Petrified Forest National Park have been identified by paleontologists as that of the oldest known frogs in North America.
The fossils are composed of several small pieces of hip bone, called an ilium, from Chinle frogs, a distant, long-extinct branch, but not a direct ancestor of, modern frogs, according to a Virginia Tech press release.
The fragments are packed into rock and are smaller than a pinky nail. They represent the first known and earliest equatorial remains of a salientian — the group containing living frogs and their most-closely related fossil relatives — from the Late Triassic, roughly 216 million years ago.
Discovered in May 2018, the fossils underscore the importance of microfossil collection and analysis for understanding extinct species whose total length is under three feet in length, said Michelle Stocker, an assistant professor of geosciences in the Virginia Tech College of Science.
The bones of the frogs show that they were really tiny — just a bit over half-an-inch long. “The Chinle frog could fit on the end of your finger,” Stocker added.
The research, led by Virginia Tech’s Michelle Stocker and Sterling Nesbitt, Arizona’s Petrified Forest National Park, and the University of Florida’s Museum of Natural History, were published today in the online journal Biology Letters. Even though the fossils are part of the Chinle frog family, the scientists are not yet naming the specific fossils.
“We refrain from naming this Chinle frog because we are continuing to process microvertebrate matrix that will likely yield additional skull and postcranial material that has the potential to be even more informative,” Stocker said.
According to the scientists, the Chinle frog actually shares more features with living frogs and Prosalirus, an early Jurassic frog found in sediments from the present-day Navajo Nation, than to Triadobatrachus, an Early Triassic frog found in modern day Madagascar in Africa.
“These are the oldest frogs from near the equator,” Stocker said. “The oldest frogs overall are roughly 250 million years old from Madagascar and Poland, but those specimens are from higher latitudes and not equatorial.”
The discovery also marks the first time that frog fossils have been found directly with phytosaurs and other early dinosaurs.