An alternative interpretation of small-bodied turtles from the “Middle Purbeck” of England as a new species of compsemydid turtle

Abstract

A series of small-sized fossil turtles were collected from Beckles’ Pit, Durlston Bay, Dorset, United Kingdom in 1856 from a sediment package referable to the Early Cretaceous (Berriasian) Purbeck Group. The two primary accounts that previously documented these turtles concluded that they represent the juveniles of the coeval early pleurosternid Pleurosternon bullockii. A brief, third account, however, suggested that these may represent a new species of compsemydid turtle. We here highlight a series of discrete morphological characters that consistently distinguish the small-bodied turtles from Beckles’ Pit from large-bodied Pleurosternon bullockii, in particular the arrangement of the bones and scutes along the anterior margin of the shell. As these characters are otherwise used to diagnose new species of turtles, in particular compsemydids, and to establish the phylogeny of fossil turtles, we side with the latter interpretation and name a new taxon of early compsemydid, Tongemys enigmaticagen. et sp. nov. The early record of compsemydid is restricted to the Early Cretaceous of Europe, but is extremely fragmentary. We suggest that this may be a bias towards the collection and identification of small turtle remains, but also that a re-study of Early Cretaceous continental turtle faunas is likely to yield further material.

Mandibular anatomy of the paracryptodire Glyptops ornatus supports active hunting behavior in a Jurassic turtle

“…Paracryptodiran phylogeny likely suffers from taphonomic artifacts that are common in turtles: some fossil species are only known from skulls (e.g., Arundelemys dardeni : Evers et al, 2021; Lipka et al, 2006, Uluops uluops : Carpenter & Bakker, 1990; Rollot et al, 2021a), whereas others do not preserve skull material and are primarily known from shells (e.g., Toremys cassiopeia : Pérez‐García et al, 2015; Selenemys lusitanica : Pérez‐García & Ortega, 2011). Only relatively few specimens are known from more complete material that includes the skull and shell, but these are often either not well preserved, incompletely described, or taxonomic referrals have been controversial (e.g., Compsemys victa : Gilmore, 1919; Lyson & Joyce, 2011, Dinochelys whitei : Gaffney, 1979b, Glyptops ornatus : Gaffney, 1979b, Pleurosternon bullockii : e.g., Evans & Kemp, 1975; Evers et al, 2020; Guerrero & Pérez‐García, 2021; Joyce et al, 2022; Milner, 2004). Recovering new anatomical details from these species may be important in stabilizing paracryptodiran phylogeny by documenting variation that has previously not been phylogenetically considered.…”

The Australian gulf snapping turtle Elseya lavarackorum (Testudines: Chelidae) revisited—Is the late Pleistocene fossil species extant?

“…Characterization of morphological variation in the shells of extant Elseya can provide a baseline for interpretation of the character states of fossil specimens. However, other studies of this type serve to highlight the difficulties inherent in recognizing and accommodating intraspecific diversity in the fossil record (Vitek 2018;Guerrero and Pérez-García 2021;Joyce et al 2022;Liaw and Tsai 2022). This challenge becomes particularly acute when relatively few fossil specimens are available.…”