Identification and Taphonomy of a Miocene Leatherback Turtle (Testudines: Dermochelyidae) from the Westerschelde, The Netherlands

Abstract

The Westerschelde Estuary in The Netherlands is rich in vertebrate fossil content. In a recent trawling campaign aimed to sample a vertebrate assemblage, over 5000 specimens have been retrieved, all currently in the possession of the Natuurhistorisch Museum Rotterdam. One specimen is a fragment of a dermochelyid sea-turtle carapace. The Westerschelde is hereby the second locality to confirm the presence of dermochelyids in the Miocene North Sea. The Westerschelde fragment is described and identified as Psephophorus polygonus Meyer, 1847. The various secondary marks present on the carapace fragment are suggestive of both predatory and scavenging origin. In order to estimate the size of the Westerschelde specimen, two Dermochelys coriacea specimens from The Royal Belgian Institute of Natural Sciences have been analysed. Based on the assumption that Psephophorus has 7 longitudinal ridges on its carapace similar to D. coriacea, the size of the complete carapace is estimated to have been 168 *126 cm. Based on the physical traits of the Westerschelde specimen, and a re-examination of P. polygonus specimens from the Naturhistorisches Museum Wien, it is argued that previously assigned characteristics are not discriminative taxonomic properties of dermochelyids in general and of P. polygonus in particular. An improved cladistic analysis on dermochelyids is performed based on previously defined-, and new taxonomic characters. With use of the cladistic analysis it is argued that Psephophorus calvertensis Palmer, 1909 as well as the Westerschelde specimen can be assigned to Psephophorus polygonus, which can thus be proven to be cosmopolitan, similar to the extant species Dermochelys coriacea.