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.
Highlights
Pliosaurid plesiosaurs were highly successful aquatic predatory amniotes that represented significant components of Mesozoic marine ecosystems
Whereas the Middle to Late Jurassic pliosaurid record is relatively abundant (e.g., Knutsen, 2012; Knutsen, Druckenmiller & Hurum, 2012; Benson et al, 2013), the Cretaceous pliosaurids are represented by only a few taxa, most or all of which belong to a single lineage
The third part includes an assessment of the morphological variability in the teeth regarded as representing Polyptychodon interruptus
Summary
Pliosaurid plesiosaurs were highly successful aquatic predatory amniotes that represented significant components of Mesozoic marine ecosystems. Whereas the Middle to Late Jurassic pliosaurid record is relatively abundant (e.g., Knutsen, 2012; Knutsen, Druckenmiller & Hurum, 2012; Benson et al, 2013), the Cretaceous pliosaurids are represented by only a few taxa, most or all of which belong to a single lineage. Our knowledge of brachauchenine origins, interrelationships, paleoecology, and paleobiogeography is rather poor. In part, this might be due to scarce fossil material of the oldest known members of this clade (Hampe, 2005; Fischer et al, 2015) and low taxic diversity in the Early Cretaceous (Benson et al, 2010). Other reasons might include general absence of detailed taxonomic assessments of the Cretaceous pliosaurid record
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