Pleurochayah appalachius: Fossil of North America’s Earliest Side-Necked Turtle Unearthed
A new genus and species of side-necked turtle that lived 96 million years ago (Cenomanian age of the Late Cretaceous period) has been identified from the fossilized remains found in Texas. This discovery suggests that side-necked turtles — those that withdraw their necks sideways into their shells when threatened — migrated to North America during the Cenomanian age, between 100 and 94 million years ago.
The group originated in the southern continent of Gondwana, migrating to northern continents beginning in the Early Cretaceous.
Named Pleurochayah appalachius, the new turtle is one of the earliest examples of intercontinental dispersals by the group and is the oldest bothremydid found in North American and Laurasian sediments.
“This discovery provides the earliest evidence of side-necked turtles in North America and expands our understanding of the first migrations of the extinct bothremydids,” said lead author Dr. Brent Adrian, a researcher in the Department of Anatomy at Midwestern University.
The fossilized remains of Pleurochayah appalachius were discovered at the Arlington Archosaur Site of the Woodbine Group in Texas, the United States.
They predate Paiutemys tibert, a turtle species from Utah that was previously recognized as the oldest known North American side-necked turtle.
“The discovery further establishes the Arlington Archosaur Site as an important fossil unit that is revealing the foundations of an endemic Appalachian fauna,” Dr. Adrian noted.
Pleurochayah appalachius had an intriguing combination of morphological adaptations to a highly aquatic lifestyle that likely facilitated its long-distance migration.
Its upper arm bone shows large bony attachments for muscles that support a powerful recovery from swimming strokes.
The functional morphology of the bone also indicates that the turtle likely utilized an aquatic rowing mode of swimming, as opposed to the flapping motion of modern sea turtles.
The microanatomy of its shell bone reveals a comparatively thick external compared to internal cortex, similar to later marine-adapted bothremydid species.
However, its marine adaptations are not as derived as in later bothremydids, which are found throughout the fossil record of North American later in the Late Cretaceous.
The skull of Pleurochayah appalachius had a unique combination of primitive and derived traits that it shares with other bothremydid species.
Based on the findings, Dr. Adrian and colleagues suggest that early bothremydid turtles migrated from Gondwana to North America during or prior to the Cenomanian age via the central Atlantic Ocean or the Caribbean.
“It is likely that bothremydid dispersals to North America during or prior to the Cenomanian were influenced by the vicariant event of the opening of the central Atlantic, and the periodic connection of the Western Interior Seaway to the Gulf of Mexico,” the paleontologists said.
“However, allopatric speciation may be responsible for the multiple-continent distribution of basal bothremydids, as demonstrated for other Late Early Cretaceous pelomedusoid clades.”
The study was published in the journal Scientific Reports.
B. Adrian et al. 2021. An early bothremydid from the Arlington Archosaur Site of Texas. Sci Rep 11, 9555; doi: 10.1038/s41598-021-88905-1