Léa C. Girard - New perspectives on the evolution of pan-trionychids based on the study of plastomenid skulls

SCIMED - Geosciences - Turtle Evolution Symposium 2024

12:51, 1 July, English, 1 view

Soft shell turtles (Pan-Trionychidae) can be recognized by the unique morphology of their shell, which is highly reduced and covered with a thick leathery skin, rather than scales. This aquatic clade likely originated during the Early Cretaceous in Asia and today is spread across parts of Africa, Asia,Australasia, and North America. Extant representatives of the group closely resemble their earliest relatives, leading to difficulties in discerning phylogenetic relationships. In addition, the detailed cranial anatomy is only known for few fossil taxa. The evolutionary history of the group is, therefore, still poorly understood. Plastomenidae is an extinct North American subclade of Pan-Trionychidae characterized, among others, by a secondary reossification of the plastron and a prolonged midline contact between the maxillae that forms a secondary palate. Until recently, the skulls of plastomenids were barely figured and described in the literature. We examined the cranial morphology of Hutchemys rememdium, a potential plastomenid, based on micro-computed tomography (μCT) scans of undescribed skulls and jaws from the Paleocene of North Dakota. A phylogenetic analysis following the inclusion of the new material supports the identity of Hutchemys rememdium as a plastomenid, but still supports the somewhat questionable placement of Plastomenidae as sister to Cyclanorbinae. Our current work aims to expand our data set through the study of additional μCT scans obtained from other potential Late Cretaceous and Paleogene plastomenids, including those of Atoposemys superstes, Aspideretoides foveatus, and “Trionyx” allani.

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