The oldest tree-climbing reptile on record has been discovered in New Mexico

June 21—It’s a story that has been brewing for 305 million years.

The one that was hidden deep in the Cañon del Cobre in the southeastern part of Rio Arriba county.

Its name is Eoscansor.

On Tuesday, the New Mexico Museum of Natural History and Science announced that a team of paleontologists, including several from the museum, had discovered a fossil of the oldest tree-climbing reptile on record.

“Once again, a New Mexico fossil find is rewriting the textbooks of paleontology,” said Spencer G. Lucas, curator of paleontology at NMMNHS. “In this case, revealing a nimble little climber who is a previously unexpected inhabitant of the Pennsylvanian world.”

The reptile was named Eoscansor, from the Greek roots eo (“dawn”) and scansor (“climber”).

Lucas said Eoscansor is a eupelycosaur, a group of extinct reptiles that includes the familiar sail-backed reptile Dimetrodon, which is often mistaken for a dinosaur.

However, eupelycosaurs are more closely related to mammals than to dinosaurs.

According to the report, numerous anatomical features of the fossil skeleton, particularly the limbs, hands and feet, indicate that it almost certainly climbed trees. Its teeth indicate that it was a predator that probably ate insects. Eoscansor would have been a very agile little climber, and its discovery likely means that many other climbing reptiles remain to be discovered.

Research from NMMNHS and the Carnegie Museum of Natural History describing the 305-million-year-old fossil was published in the scientific journal Annals of the Carnegie Museum.

According to the report, the history of arboreality of tetrapods (living in trees) has long been discussed.

“This animal is a new genus and species of varanopid eupelycosaur…To establish its scansoriality (climbing), we provide various osteological criteria based on an examination of skeletal traits indicative and consistent with scansoriality in living and extinct tetrapods , especially in lizards,” the report said. “The new varanopid is the oldest known scansorial tetrapod capable of grasping and contributes to the growing diversity and disparity of varanopid eupelycosaurs.”

Lucas said the fossil was discovered in 2005.

“…but (the team) didn’t really prepare and study it until 2015. We knew what we had in 2019 and then the pandemic derailed us,” Lucas said.

Other members of the research team include NMMNHS research associates Larry F. Rinehart and Matthew D. Celeskey, as well as Carnegie Museum of Natural History curator emeritus David S Berman and collections manager Amy C. Henrici.

The fossil is now part of the NMMNHS collection.

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