When you think of an amphibian, the first thing that probably comes to mind is an elastic frog or a salamander or maybe a cane toad. But some recently discovered fossils of a lesser-known amphibian order called Caecilians — limbless, worm-like creatures that live and burrow underground — could fill in big evolutionary gaps in how amphibians live today. today appeared.

Caecilians look a bit like large earthworms and there are over 124 known species. Like all amphibians, they feel at home in water and on land. Modern Caecilians now live exclusively in South Asia, South and Central America, and parts of Africa. Their enigmatic underground lives make them difficult for scientists to study, and although they can live up to 13 years in captivity, it’s unclear exactly how long they live in the wild.

[Related: These pleasantly plump salamanders dominated the Cretaceous period.]

Previously, only 10 fossil Caecilian occurrences had been discovered by scientists, and they date back approximately 183 million years to the Early Jurassic.

Now a team of paleontologists has unearthed a new and older Cecilian fossil, extending the record for this tiny animal by around 35 million years, all the way back to the Triassic period (around 250-200 million ago). of years). This fossil has a reddish hue and offers some clues as to what the strange family of creatures might have looked like. The discovery of fossils is described in a study published on January 25 in the journal Nature.

Vermiform fossil from the Triassic could fill a hole in amphibian evolutionary history
Microscopic photograph of a Funcusvermis gilmorei lower jaw shortly after it was recovered during microscopic sorting of sediment from the Thunderstorm Ridge fossil site in the Paleontology Laboratory at Petrified Forest National Park. CREDIT: Photo by Ben Kligman for Virginia Tech.

“Seeing the first jawbone under the microscope, with its distinctive double row of teeth, sent shivers down my spine,” Ben Klingman, a Virginia Tech doctoral student and co-author of the new study, said in a statement. “We immediately knew it was a caecil, the oldest caecil fossil ever found, and a once-in-a-lifetime find.”

Klingman named the new fossil “Funcusvermis gilmorei”. The genre name “Funcusvermis” was inspired by an Ohio Players song called “Funky Worm”, a favorite dig song of the authors.

mushroom worm shares some skeletal features with the earliest frog and salamander fossils and an ancient group of amphibians called the dissorophoid temnospondyls. “Unlike living caecilians, Funcusvermis lacks many adaptations associated with underground burial, indicating a slower acquisition of features associated with a subterranean lifestyle in the early stages of caecilian evolution,” Klingman said.

The find was found in Arizona’s Petrified Forest National Park during a 2019 dig. The fossils were found in a part of the park dubbed Thunderstorm Ridge, which is well known for its fossil finds. They were deposited in a layer of the Chinle Formation dated to around 220 million years ago. At the time, the state of Arizona was near the equator in the central part of the ancient supercontinent Pangea. Like today, the area was warm, but unlike today, it was much wetter.

[Related: This fossil-sorting robot can identify millions-year-old critters for climate researchers.]

At least 70 individuals of Funcusvermis were recovered in the summer of 2022 from Petrified Forest National Park. Only a handful of Funcusvermis bones have been found, but until the team can find a complete skeleton, they cannot determine the exact body length of Funcusvermis. Early deductions estimate that he was quite small since the remains of his lower jaws are less than a quarter inch long.

“The discovery of the oldest Caecilian fossils highlights the crucial nature of new fossil evidence. Many of the biggest open questions in paleontology and evolution cannot be answered without fossils like this,” Kligman said. “Fossil caecilians are extraordinarily rare, and are found incidentally when paleontologists search for fossils of other more common animals.”

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