Funcusvermis gilmorei lived in the tropical forests of what is now Arizona, the United States, during the Triassic period, approximately 220 million years ago.

Life reconstruction of Funcusvermis gilmorei (foreground) and the crocodile relative Acaenasuchus geoffreyi (background) in the tropical forest of Petrified Forest National Park about 220 million years ago. Image credit: Andrey Atuchin / U.S. National Park Service / Petrified Forest Museum Association.

Living amphibians (subclass Lissamphibia) include frogs and salamanders (order Batrachia) and the limbless worm-like caecilians (order Gymnophiona).

Caecilians have cylindrical bodies with a compact, bullet-shaped skull that helps them burrow underground.

Now exclusively home to South and Central America, Africa, and southern Asia, they spend their lives burrowing in leaf-litter or soil searching for prey such as worms and insects.

Prior to the discovery of Funcusvermis gilmorei, only 10 fossil caecilian occurrences were known, dating back to the Early Jurassic epoch, about 183 million years ago.

However, previous DNA studies estimated evolutionary origins of caecilians back to the Carboniferous or Permian periods, some 370 million to 270 million years ago, marking that 87-million-year gap. However, no such fossils had been found.

“The discovery of the oldest caecilian fossils highlights the crucial nature of new fossil evidence,” said Ben Kligman, a doctoral student in the Department of Geosciences at Virginia Tech.

“Many of the biggest outstanding questions in paleontology and evolution cannot be resolved without fossils like this.”

“Fossil caecilians are extraordinarily rare, and they are found accidentally when paleontologists are searching for the fossils of other more common animals.”

The fossilized remains of Funcusvermis gilmorei were found in the Upper Triassic Chinle Formation in Petrified Forest National Park, Arizona.

“Funcusvermis gilmorei was found in a layer of the Chinle Formation dated to approximately 220 million years ago, when Arizona was positioned near the equator at the central part of the supercontinent Pangea,” Kligman said.

“Seeing the first jaw under the microscope, with its distinctive double row of teeth, sent chills down my back.”

“We immediately knew it was a caecilian, the oldest caecilian fossil ever found, and a once-in-a-lifetime discovery.”

Funcusvermis gilmorei shares skeletal features related more with early frog and salamander fossils, strengthening evidence for a shared origin and close evolutionary relationship between caecilians and these two groups.

It also shares skeletal features with an ancient group of amphibians known to paleontologists as dissorophoid temnospondyls.

“Unlike living caecilians, Funcusvermis gilmorei lacks many adaptations associated with burrowing underground, indicating a slower acquisition of features associated with an underground lifestyle in the early stages of caecilian evolution,” Kligman said.

Source: sci.news