title: First report of Plesiochelys etalloni and Tropidemys langii from the Late Jurassic of the UK and the palaeobiogeography of plesiochelyid turtles.
abstract: Plesiochelyidae is a clade of relatively large coastal marine turtles that inhabited the shallow epicontinental seas that covered western Europe during the Late Jurassic. Although the group has been reported from many deposits, the material is rarely identified at the species level. Here, we describe historical plesiochelyid material from the Kimmeridge Clay Formation of England and compare it with contemporaneous localities from the continent. An isolated basicranium is referred to the plesiochelyid Plesiochelys etalloni based notably on the presence of a fully ossified pila prootica. This specimen represents the largest individual known so far for this species and is characterized by remarkably robust features. It is, however, uncertain whether this represents an ontogenetic trend towards robustness in this species, some kind of specific variation (temporal, geographical or sexual), or an abnormal condition of this particular specimen. Four other specimens from the Kimmeridge Clay are referred to the plesiochelyid Tropidemys langii. This contradicts a recent study that failed to identify this species in this formation. This is the first time, to the best of our knowledge, that the presence of Plesiochelys etalloni and Tropidemys langii is confirmed outside the Swiss and French Jura Mountains. Our results indicate that some plesiochelyids had a wide palaeobiogeographic distribution during the Kimmeridgian.
authors.affiliation: JURASSICA Museum, Route de Fontenais 21, 2900 Porrentruy, Switzerland; Department of Geosciences, University of Fribourg, Chemin du Musée 6, 1700 Fribourg, Switzerland; Section d'archéologie et paléontologie, Office de la culture, République et Canton du Jura, Hôtel des Halles, 2900 Porrentruy, Switzerland.
authors.forename: Jérémy
authors.identifier: 0000-0001-5539-8691
authors.initials: J
authors.lastname: Anquetin
authors.affiliation: Department of Earth Sciences , The Natural History Museum , Cromwell Road, London SW7 5BD, UK.
authors.forename: Sandra D
authors.initials: SD
authors.lastname: Chapman
keywords: Kimmeridge Clay; Kimmeridgian; Late Jurassic; Plesiochelyidae; Plesiochelys etalloni; Tropidemys langii