New research of two tiny fossils found in the 1990s has helped scientists reveal the backstory of the most mysterious amphibian alive and expand amphibious timeline by at least 15 million years.
Dubbed Chinlestegophis jenkinsi, the pair of fossils is the oldest relative of the most mysterious group of amphibians: caecilians. Today, these limbless, colorful serpentine carnivores live underground and range in size from 6 inches to 5 feet, according to the new research.
The study, published this week in Proceedings of the National Academy of Sciences, expands the known history of frogs, toads and salamanders by at least 15 million years and closes a significant gap in early caecilian evolution by connecting them to stereospondyls, animals with toilet-seat heads that were the most diverse amphibian group during the Triassic era more than 200 million years ago.
Scientists found that the fossils of the extinct species from the Triassic Period are the long-missing link that connects Kermit the Frog's amphibian brethren to wormlike creatures with a backbone and two rows of sharp teeth.
"Our textbook-changing discovery will require paleontologists to re-evaluate the timing of the origin of modern amphibian groups and how they evolved," Adam Huttenlocker, senior author of the study and an assistant professor at the Keck School of Medicine of University of Southern California, said in a statement.
There are currently fewer than 200 modern species of caecilians, which live in the wet, tropical regions of South America, Africa and Southeast Asia.
But the two ancient fossil amphibians found in the late 1990s by Bryan Small, study co-author and a research associate at Texas Tech University, were preserved in the fossilized burrows of Eagle County, Colorado.
The paleontologists used 3-D X-rays to reassemble the fossil remains of a now-extinct species that walked the Earth 200 million years ago.
"Twenty to 30 years ago, we weren't even sure of the origins of birds," Pardo said. "Now we are solving some of the final remaining mysteries when it comes to what sorts of animals the major vertebrate groups evolved from. Caecilians, turtles and some fish are the only major vertebrate groups that paleontologists still have questions about."
Scientists previously believed the story of the stereospondyl order was a dead-end because, although widespread during the Triassic Period, the animals were believed to be unrelated to anything alive today.
The two recently discovered fossils finally fill this gap and suggest that the amphibian lineage of today evolved from a common ancestor some 315 million years ago.