Paleontologists have found a new sea turtle species from the Cretaceous epoch which they believe to be an ancestor of all modern turtles.

This is a reconstruction of the new species (Peritresius martini). Image credits: Drew Gentry.

If you look at turtles today, it’s easy to guess that they’ve been around for a very long time. Like crocodiles and other reptiles, they had ancestors that lived alongside the dinosaurs in the Mesozoic times. Such an ancestor was Peritresius ornatus, who lived in North America during the Late Cretaceous epoch — from around 100 to 66 million years ago. Researchers thought that P. ornatus was the sole member of its group but now, a new study has found a sister species.

Named Peritresius martini after its discoverer, George Martin, the species was discovered based on fossils found in Alabama, US. Its shell measured over 90 cm long and 75 cm wide, which is far larger than known P. ornatus specimens. Researchers also note that the P. martini shell was rather plain, whereas the P. ornatus one had sculptured skin elements that were supported by blood vessels. This feature suggests that P. ornatus was capable of thermoregulation, self-regulating its body temperature based on the environmental conditions. This might have allowed it to keep warm and survive the global cooling that occurred throughout the Late Cretaceous, unlike most turtles, which went extinct.

“The heavily vascularized and sculptured dermal elements characteristic of P. ornatus are interpreted here as potentially indicative of a thermoregulatory capability and may have been one of the key factors contributing to the survival of Peritresius into the Maastrichtian, a period of cooling when other lineages of Campanian marine turtles (e.g., Protostegids, Toxochelys, and Ctenochelys) went extinct,” the study authors write.

The finding also shows that turtles belonging to this clade were far more widespread than previously believed. It’s unclear if other species belonging to the group existed.

Lead author Drew Gentry says:

“This discovery not only answers several important questions about the distribution and diversity of sea turtles during this period but also provides further evidence that Alabama is one of the best places in the world to study some of the earliest ancestors of modern sea turtles.”

Journal Reference: Gentry AD, Parham JF, Ehret DJ, Ebersole JA (2018) A new species of Peritresius Leidy, 1856 (Testudines: Pan-Cheloniidae) from the Late Cretaceous (Campanian) of Alabama, USA, and the occurrence of the genus within the Mississippi Embayment of North America. PLoS ONE 13(4): e0195651. https://doi.org/10.1371/journal.pone.0195651