If you’ve ever seen a sea turtle, you’ll not be surprised to hear that these creatures have ancestors dating back to the times of dinosaurs. One ancestor of modern-day sea turtles, Peritresius ornatus, lived in North America during the Late Cretaceous epoch, from around 100 to 66 million years ago. P. ornatus was thought to be the sole member of the Peritresius group at that time, but a new PLOS ONE study has found a sister species.
Named Peritresius martini after its discoverer, George Martin, the species was identified from fossils in marine sediments in Alabama. In the new study, Andrew Gentry from the University of Alabama at Birmingham, Alabama, USA, and colleagues describe P. martini and compare it to P. ornatus. The scientists estimate P. martini’s shell at over 90 cm long and 75 cm wide, far larger than known P. ornatus specimens.
The researchers’ comparison also suggested that the known species, P. ornatus, may be especially unusual: its shell is distinct not just from P. martini but also from other Cretaceous sea turtles, featuring sculptured skin elements that appear to have been well-supplied with blood vessels. This unique feature may suggest that P. ornatus was capable of thermoregulation, which could have enabled the turtle to keep warm and survive global cooling that occurred throughout the Late Cretaceous, unlike many other marine turtles that went extinct.
Since few Peritresius fossils from this epoch had previously been found in the southeastern U.S., these findings reveal that Peritresius was distributed across a wider region than previously thought. In finding a sister species to P. ornatus, the research also extends the known evolutionary history of the lineage that led to the sea turtles with which we’re so familiar today.
Research Article: 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
Image Credit: Gentry et al, 2018