A reassessment of the Late Jurassic turtle Eurysternum wagleri (Eucryptodira, Eurysternidae)

Eurysternum wagleri is one of the first named, yet most poorly understood turtles from the Late Jurassic of Europe. Over the years, many specimens have been referred to and many species synonymized with E. wagleri, but little consensus is apparent, and the taxonomy is therefore highly confusing. Based on the rare, only known illustration of the lost holotype and on the reassessment of select individuals, the species E. wagleri is recharacterized herein. Eurysternum wagleri is diagnosed by a deep pygal notch, a carapace with a pentagonal outline, a contribution of vertebral 5 to the posterior carapace margin, three cervical scales, very wide vertebral scales with a well-developed radiating pattern, well-developed costoperipheral fontanelles in medium-sized individuals, a plastron connected to the carapace by ligaments, gracile, peg-like bony projections of the hyo- and hypoplastra, and large, oval-to-quadrangular lateral plastral fontanelles. A lectotype is designated for Acichelys redenbacheri, and this taxon is interpreted as the junior subjective synonym of Eurysternum wagleri. All other, previously proposed synonymies are rejected, because they lack characters that would allow diagnosing them as E. wagleri.