Desmatochelys


Desmatochelys is an extinct genus of sea turtles belonging to the family Protostegidae. This genus contains two known species, D. lowii and D. padillai. D. lowii was first discovered in 1895, followed by D. padillai in 2015. Having been estimated at over 120 million years old, D. padillai is currently the oldest known species of sea turtle.
Desmatochelys lived during the Cretaceous, and had a wide geographic range, primarily along the Western Interior Seaway.

Discovery

The first specimen of Desmatochelys was described by Samuel Wendell Williston in the Kansas University Quarterly in 1895. In his article he describes its discovery by a railroad worker near Fairbury, Nebraska. Williston was granted access to the specimen by his colleague M. A. Low, giving rise to the name ‘lowii’. This specimen was from the Late Cretaceous Benton Formation and included a nearly complete skull and lower jaw as well as pieces of the limbs, carapace, and plastron. Since first being discovered, at least five new specimens of D. lowii have been described, found in South Dakota, Kansas, Arizona, Canada, and Mexico.
D. padillai was first described in 2015 by paleontologists from the Senckenerg Research Institute and California State University. It was discovered in Colombia with the Lower Cretaceous Paja Formation. This placed its age around 120 million years, making it the oldest known sea turtle, a title which was previously held by Santanachelys gaffneyi.

Description

Desmatochelys was a large sea turtle, with some specimens reaching up to 2 meters long. Members of the genus are characterized by the extended skull roof, large nasal bones, and a paddle-like humerus, as well as a distinct body shell or carapace and reduced plastron like other protostegids.
Specimens of Desmatochelys have been found in Nebraska, South Dakota, Kansas, Arizona, Canada, Colombia, and Mexico. They are known to have existed along the Western Interior Seaway during the Late Cretaceous, and their range may have extended to the Pacific coast. Desmatochelys, like modern sea turtles, had a wide geographic distribution within the oceans.
As for its stratigraphic distribution, it is generally accepted that Desmatochelys was restricted to the Cretaceous, with occurrences ranging from the Barremian to the Campanian.
Nothing is known of this turtle's reproductive strategy, with the exception of their egg development. Desmatochelys is hypothesized to have laid rigid eggs instead of the soft-shelled eggs typical of extant marine turtles, as a closely related protostegid has been shown to do.

Taxonomy

The genus contains the following species:
Initially, Desmatochelys formed its own family, Desmatochelydae. Later it was reassigned into the family Protostegidae. There is some debate among the paleontological community over the placement of Protostegidae within turtle phylogeny. According to Elizabeth L. Nicholls, the genus should also be expanded to include closely related members that currently belong to Notochelone and Rhinochelys. As of 2019, Desmatochelys contains the two previously stated species, is within the family Protostegidae, and is placed along the stem of Chelonioidea - in other words, it is considered a basal turtle genus.