Desmatochelys

The first specimen of Desmatochelys was described by Samuel Wendell Willy 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.[6] Since first being discovered, at least five new specimens of D. lowii have been described, found in South Dakota, Kansas, Arizona, Canada, and Mexico.[5]

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.[4]

Desmatochelys was a large sea turtle, with some specimens reaching up to 2 meters long.[4] 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.[7]

A large fossil skeleton of Desmatochelys padillai is presented on a bed of sand

Specimens of Desmatochelys have been found in Nebraska, South Dakota, Kansas, Arizona, Canada, Colombia, and Mexico.[5] 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.[5]

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.[8]

The genus contains the following species:

• Desmatochelys lowi
• Desmatochelys padillai

Initially, Desmatochelys formed its own family, Desmatochelydae.[6] Later it was reassigned into the family Protostegidae. There is some debate among the paleontological community over the placement of Protostegidae (and therefore Desmatochelys) within turtle phylogeny.[4][9][10] According to Elizabeth L. Nicholls, the genus should also be expanded to include closely related members that currently belong to Notochelone and Rhinochelys.[11][12][10] 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.[4][13]