Newly Discovered Fossils Fill Gaps in Amphibian Evolution

CC BY-SA 3.0. Shyamal

The newfound fossils shed light on the early evolution of one of the planet’s most mysterious amphibians.

Caecilians are one of the most mysterious amphibians on earth. This group of limbless, serpentine carnivores can range in size from 6 inches to 5 feet and primarily live underground in wet, tropical areas across Africa, South America, and Southeast Asia. Although there are currently about 200 known species of caecilians, little is known about their early evolution.

“Caecilians, turtles and some fish are the only major vertebrate groups that paleontologists still have questions about,” explained Jason Pardo, a doctoral candidate in the Faculty of Veterinary Medicine at the University of Calgary in Alberta, Canada. “Caecilians are hard to find in the fossil record because most are so small,” added Adam Huttenlocker, an assistant professor in the Department of Integrative Anatomical Sciences at the Keck School of Medicine of USC.

Bryan Small, a research associate at Texas Tech University, discovered two caecilian fossils from the late Mesozoic Era in the 1990s in Eagle County, Colorado, but these fossils had reduced limbs and resembled the caecilians of today, leaving questions about the amphibians’ early evolution unanswered.

However, Small, Pardo, and Huttenlocker recently discovered two new caecilian fossils from the Triassic Period in central Colorado. Named Chinlestegophis jenkinsi, the new fossils act as a sort of “missing link,” connecting caecilians to stereospondyls, the most diverse amphibian group during the Triassic Period over 200 million years ago.

The skulls of the new fossils were slightly under 1 inch long, implying that C. jenkinsi were about the size of a small salamander, according to Huttenlocker. “Chinlestegophis jenkinsi still preserves a lot of the primitive morphology that is shared with other Triassic amphibians, namely their four legs," he added. The ancient amphibian probably ate insects and possessed tiny but functional eyes, differentiating it from modern caecilians, as many modern species either do not have eyes or hide their eyes under moist skin.

“Our textbook-changing discovery will require paleontologists to re-evaluate the timing of the origin of modern amphibian groups and how they evolved,” Huttenlocker noted. Prior to the discovery of the fossils, stereospondyls were believed to be unrelated to any creatures living today. However, these newfound fossils suggest that the amphibians of today evolved from a common ancestor about 315 million years ago.

Pardo argued that the discovery of the fossils could be beneficial to humans. “It’s possible that the things that frog and salamander tissue can do when it comes to scarless healing are also present in human DNA but may be turned off,” he explained. “Because humans are also vertebrates, we enhance our understanding of our own evolutionary history and genetic heritage when we gain understanding of the amphibian lineage.”