A conserved tooth resorption mechanism in modern and fossil snakes

Whether snakes evolved their elongated, limbless bodies or their specialized skulls and teeth first is a central question in squamate evolution. Identifying features shared between extant and fossil snakes is therefore key to unraveling the early evolution of this iconic reptile group. One promising candidate is their unusual mode of tooth replacement, whereby teeth are replaced without signs of external tooth resorption. We reveal through histological analysis that the lack of resorption pits in snakes is due to the unusual action of odontoclasts, which resorb dentine from within the pulp of the tooth. Internal tooth resorption is widespread in extant snakes, differs from replacement in other reptiles, and is even detectable via non-destructive mu CT scanning, providing a method for identifying fossil snakes. We then detected internal tooth resorption in the fossil snake Yurlunggur, and one of the oldest snake fossils, Portugalophis, suggesting that it is one of the earliest innovations in Pan-Serpentes, likely preceding limb loss. Living snakes replace their teeth without external resorption. Here, the authors use histology to show that odontoclasts resorb dentine internally and investigate this mechanism in fossil snakes.

Automated summary

The central question in squamate evolution is whether snakes evolved their elongated, limbless bodies or their specialized skulls and teeth first. The authors use histology to show that odontoclasts resorb dentine internally and investigate this mechanism in fossil snakes, providing a method for identifying fossil snakes. They also detect internal tooth resorption in the fossil snake, Yurlunggur, suggesting it is one of the earliest innovations in Pan-Serpentes, likely preceding limb loss.