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The last surviving Thalassochelydia—A new turtle cranium from the Early Cretaceous of the Purbeck Group (Dorset, UK)use asterix (*) to get italics
Jérémy Anquetin, Charlotte André
<p>**Background.** The mostly Berriasian (Early Cretaceous) Purbeck Group of southern England has produced a rich turtle fauna dominated by the freshwater paracryptodires *Pleurosternon bullockii* and *Dorsetochelys typocardium*. Each of these species is known by numerous relatively complete shells and by a single cranium. The two other turtles found in the Purbeck Group (**Hylaeochelys belli**, a species of uncertain affinities, and the terrestrial helochelydrid "*Helochelydra*" *anglica*) are known only from shell remains. **Methods.** In the present contribution, we describe a new turtle cranium from the Purbeck Group of Swanage, Dorset (southern England). We also explore the phylogenetic relationships of this new cranium and of *Hylaeochelys belli* in the context of a recently published global turtle matrix. **Results.** Before complete preparation, the new Purbeck cranium was provisionally referred to *Dorsetochelys typocardium*, but our analysis clearly contradicts a referral to this species in particular and to paracryptodires in general. In contrast, the new cranium shares a number of features with the Late Jurassic, coastal marine Thalassochelydia, including a posterolaterally open foramen palatinum posterius, a strong ridge on the posterior surface of the processus articularis of the quadrate, a strong posterior orientation of the processus articularis in ventral view, and a processus trochlearis oticum limited to the medial part of the otic chamber and bordered by a deep recess laterally. Our phylogenetic analysis confirms a placement of the new Purbeck cranium within the clade Thalassochelydia. **Discussion.** In terms of morphology, the new Purbeck cranium does not correspond to any known taxon. However, we refrain from naming a new species based on it because there is a good chance that this cranium actually belongs to the shell-based species *Hylaeochelys belli* (also recovered as a thalassochelydian in our phylogenetic analysis). Unfortunately, we lack any objective evidence to support this conclusion for the moment. In any case, the new Purbeck cranium confirms what others have previously suggested based on *Hylaeochelys belli*: thalassochelydian turtles survived the Jurassic-Cretaceous transition.</p> should fill this box only if you chose 'All or part of the results presented in this preprint are based on data'. URL must start with http:// or https://
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Paracryptodira; Thalassochelydia; Late Jurassic; Early Cretaceous; Morphology; Phylogeny
Comparative anatomy, Paleoecology, Phylogenetics, Systematics, Vertebrate paleontology
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2020-01-30 10:37:07
Hans-Dieter Sues