Anquetin Jérémy, Chapman Sandra D
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.
Department of Earth Sciences , The Natural History Museum , Cromwell Road, London SW7 5BD, UK.
R Soc Open Sci. 2016 Jan 13;3(1):150470. doi: 10.1098/rsos.150470. eCollection 2016 Jan.
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.
近龟科是一类体型相对较大的沿海海龟，它们栖息在晚侏罗世覆盖西欧的浅陆缘海。尽管该类群已在许多沉积物中被报道，但这些材料在物种层面上很少被鉴定出来。在此，我们描述了来自英国金梅尔黏土组的历史近龟科材料，并将其与来自欧洲大陆同期的地点进行比较。一个孤立的脑颅基部被归为近龟科的埃氏近龟，这主要基于完全骨化的耳柱骨的存在。这个标本代表了迄今为止已知的该物种最大的个体，其特征是具有非常粗壮的特征。然而，这是否代表该物种向粗壮化的个体发育趋势、某种特定变异（时间、地理或性别方面），还是这个特定标本的异常情况尚不确定。来自金梅尔黏土组的另外四个标本被归为近龟科的兰氏异侧龟。这与最近一项未能在该地层中鉴定出该物种的研究相矛盾。据我们所知，这是首次在瑞士和法国汝拉山脉之外确认埃氏近龟和兰氏异侧龟的存在。我们的结果表明，在基默里奇期，一些近龟科具有广泛的古生物地理分布。
