Thursday, 14 January 2021

NAOMICHELYS SPECIOSA OF THE HASLAM

Naomichelys speciosa, a new Helochelydrid turtle from the Trent River
Helochelydrids are a group of poorly known turtles from Late Jurassic to Late Cretaceous deposits in North America and Europe. It is the only known North American member of Helochelydridae.

Naomichelys is known numerous remains from western North America, most notably the holotype partial shell from the Early Cretaceous Cloverly Formation of Montana and a complete skeleton from the Antlers Formation of Texas.

The Cloverly Formation includes a number of vertebrate fossils including a diverse assemblage of dinosaur fossils. the site was designated as a National Natural Landmark by the National Park Service in 1973.

Naomichelys is a member of the family Helochelydridae. We find their fossilized remains in Late Jurassic to Late Cretaceous deposits in North America and Europe. Within North America, only the species Naomichelys speciosa is known from relatively complete material which makes comparisons between specimens from other localities challenging. Phil Currie along with co-authors Matthew J. Vavrek, Derek W. Larson, Donald B. Brinkman and Joe Morin described a new species of Helochelydrid terrestrial turtle found on the Trent River near Courtenay, British Columbia.

The new genus and species of helochelydrid turtle was based on a relatively complete shell from the marine Haslam Formation (Santonian) of Vancouver Island, British Columbia, Canada.

The new species is characterized by several distinctive shell features, notably a forward curving process on the anterior portion of the hyoplastra, strongly distinguishing it from N. speciosa. The shell is relatively small but does appear to be from a fully grown individual, suggesting that the species was generally much smaller than other known helochelydrids.

Previously most records of helochelydrids in North America had been assigned to N. speciosa, regardless of actual diagnosable characters. The presence of an additional species of helochelydrid from North America indicates that a greater diversity of the taxon was present than was previously recognized. While the interspecific relationships of helochelydrids remain difficult to fully assess, due to the lack of well-preserved specimens, this new species provides additional geographic and phylogenetic data that aids our understanding of this enigmatic group.