A reappraisal ofPolyptychodon(Plesiosauria) from the Cretaceous of England

Abstract

Pliosauridae is a globally distributed clade of aquatic predatory amniotes whose fossil record spans from the Lower Jurassic to the Upper Cretaceous. However, the knowledge of pliosaurid interrelationships remains limited. In part, this is a consequence of a few key taxa awaiting detailed reassessment. Among them, the taxon Polyptychodon is of special importance. It was established on isolated teeth from the mid-Cretaceous strata of East and South East England and subsequently associated with numerous finds of near-cosmopolitan distribution. Here the taxon is reassessed based on the original dental material from England, with special focus on a large collection of late Albian material from the Cambridge Greensand near Cambridge. The dental material is reviewed here from historical and stratigraphic perspective, described in detail, and discussed in terms of its diagnostic nature. The considerable morphological variability observed in the teeth attributed to Polyptychodon, together with a wide stratigraphic range of the ascribed material, possibly exceeding 35 Ma (early Aptian to ?middle Santonian), suggests that the taxon is based on a multispecies assemblage, possibly incorporating members of different plesiosaur clades. Due to the absence of any autapomorphic characters or unique character combinations in the original material, Polyptychodon interruptus, the type species of Polyptychodon, is considered nomen dubium. From a global perspective, Polyptychodon is viewed as a wastebasket taxon whose material originating from different localities should be reconsidered separately.

Isolated pliosaurid teeth from the Albian–Cenomanian (Cretaceous) of Annopol, Poland

“…A recent reappraisal by Madzia (2016) showed, however, that the original material attributed to P. interruptus is most likely too variable to belong to a single taxon. This conclusion was further regarded as being supported by the considerable time span between the oldest and youngest specimens assigned to P. interruptus, likely to exceed 35 Ma (early Aptian to ?middle Santonian).…”

“…In most cases, the material was attributed to the taxon Polyptychodon Owen, 1841a. However, a recent reappraisal of the original material of P. interruptus Owen, 1841b showed that the teeth associated with the taxon do not bear any autapomorphies and most likely belonged to different species or possibly even members of different larger clades (Madzia 2016). As a result, it was recommended that other specimens attributed to P. interruptus should be reconsidered as well.…”

“…The following parameters are given in the text of the description chapter (below): CH, crown height, the distance between the distalmost point at the base of the tooth crown and the crown apex; WLR, width-to-length ratio, measured adjacent to the cervix dentis (the parameter is roughly equivalent to CBR sensu Smith, Vann and Dodson 2005; applied as in Madzia 2016). Photographs of specimens were taken using a digital single-lens reflex camera Nikon D1X.…”

“…In Europe, it is dominated by isolated teeth known from numerous localities (e.g. Owen 1851;Papazzoni 2003;Marcinowski and Radwański 1983;Kear et al 2014;Bardet et al 2016;Fischer et al 2016;Madzia 2016;Sachs et al 2017). In most cases, the material was attributed to the taxon Polyptychodon Owen, 1841a.…”

“…Kear 2003;Knutsen 2012;Knutsen et al 2012;Benson et al 2013;Schumacher et al 2013;Benson and Druckenmiller 2014;Fischer et al 2015;Madzia 2016;Páramo-Fonseca et al 2016). Despite the fact that members of the clade Brachaucheninae represented the apex predators for more than 60 Ma, their fossil record is relatively poor.…”