A new Late Jurassic turtle from Spain: phylogenetic implications, taphonomy and palaeoecology

Abstract

Typescript received 26 October 2010; accepted in revised form 27 May 2011 Abstract: The Jurassic was an important period in the evo- lution of Testudinata and encompasses the origin of many clades, and this is especially true of Jurassic turtles from Wes- tern Europe. A new genus and species of Late Jurassic turtle, Hispaniachelys prebetica gen. et sp. nov. from the upper Ox- fordian of the Prebetic (Southern Spain), is described on the basis of postcranial material. The specimen is the only known tetrapod from the Mesozoic of the Prebetic and the oldest turtle from southern Europe. A mosaic of characters indicates this is a new genus: it displays basal features including dorsal epiplastral processes ⁄ reduced cleithra, no medial contact of the extragulars and a long first thoracic rib, alongside derived characters including an absence of mesoplastra and the verte- bral 3 ⁄ 4 sulcus crossing neural 5. The phylogenetic position of the new taxon is hard to resolve, and it might be either a paracryptodire or a basal testudine, but it is distinct from Plesiochelys. A complex taphonomic history is shown by a range of overlying grazing traces and bioerosion on the cara- pace. The carapace was subsequently overturned and buried ventrally up, terminating grazing activity, and was then bored by sponges before final burial. Scanning electron microscopy reveals phosphatic microspheroids associated with bacterial decay in the vascular cavities of the cancellous bone, suggest- ing the carapace may have acted as a closed microenviron- ment in which decay-derived authigenic minerals formed.