Caecilians are strange little amphibians. They look more like gooey snakes that frogs, and, due to a sparse fossil record, paleontologists have been confounded by their deep evolutionary backstory. Even though family trees made from molecular data predicted that they've been around for over 270 million years, only two early caecilian fossils have ever turned up, with even the oldest of the two still leaving a 70 million year gap between when they were supposed to have appeared and when the fossils start turning up.
Enter Chinlestegophis. Known from a pair of partial skulls found in Colorado, and described by Jason Pardo and colleagues, this amphibian pushes the fossil record of caecilians back to about 215 million years ago. Unlike its later fossil cousins, the skeleton of Chinlestegophis doesn't look quite as modern, instead have what the researchers call "a mélange" of traits in common with both caecilians and more generalized ancestors. And it's that combination that has little Chinlestegophis changing what paleontologists thought about the where caecilians came from.
When Pardo and and coauthors went about trying to place Chinlestegophis in the wider amphibian family tree - including lineages thought to be totally extinct - they found a surprise. Caecilians were closely related to a group of ancient amphibians called stereopdondyls - bulky, vaguely salamander-like amphibians with toothy jaws that opened like toilet seats. This group was supposed to be totally extinguished in the deep past, but the new study suggests that caecilians are now carrying the stereospondyl banner into our time. What's old is new again.
Fossil Facts
Name: Chinlestegophis jenkinsi
Meaning: Chinlestegophis translates to "Chinle roofed serpent", while jenkinsi is a tribute to paleontologist Farish Jenkins.
Age: Triassic, about 215 million years old.
Where in the world?: Colorado, USA.
What sort of organism?: An amphibian called a caecilian.
How much of the organism’s is known?: Two partial skulls.
Reference:
Pardo, J., Small, B., Huttenlocker, A. 2017. Stem caecilian from the Triassic of Colorado sheds light on the origins of lissamphibia. PNAS. doi: 10.1073/pnas.1706752114
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