Polycotylus latipinnis: a Redescription of Polycotylid Plesiosaur From Campanian Cretaceous South Dakota

Polycotylus latipinnis Cope (Plesiosauria, Polycotylidae), a nearly complete skeleton from the Niobrara Formation (Early Campanian) of southwestern South Dakota

Authors:

Schumacher et al

Abstract:

A nearly complete skeleton of Polycotylus latipinnis (SDSM 23020) from the upper Niobrara Formation (early Campanian) of South Dakota (U.S.A) greatly improves information for this formerly poorly known taxon. Specimens SDSM 23020 and YPM 1125 (paratype P. latipinnis) exhibit numerous postcranial characters that distinguish Polycotylus, in particular presacral vertebral count, nature of chevron facets, unique ilia, and highly derived paddles including five epipodial ossifications and increased hyperphalangy. Greater vertebral and phalangeal counts of Polycotylus are accompanied by exceptional foreshortening; thus, the relative body and limb proportions are likely similar to less derived polycotylids, with fewer, more elongate vertebrae and phalanges. The complete skull, derived among polycotylids, has short temporal fenestrae, elongate frontals, exceptionally slender parasphenoid with prominent cultriform process, and exceptionally long extensions of the angulars and splenials within the mandibular symphysis. Cladistic analysis indicates that Polycotylus nests firmly within derived Polycotylidae as a potential sister taxon to Dolichorhynchops osborni and Trinacromerum, despite a ‘primitive’ presacral vertebral count. Future improvements in available data, in particular better information regarding basal polycotylids, and refinement of character selection to nullify homoplasy could significantly alter the tree structure to show distinct subgroups within Polycotylidae. North American polycotylids with elongate temporal fenestrae, elongate podials, and relatively long vertebrae are confined to occurrences of late Cenomanian and earliest Turonian age, whereas polycotylids distinctly foreshortened in these respects are restricted to post-Turonian occurrences. Ilium morphology is highly variable among polycotylids and, in addition to taxonomic utility, may be in part attributable to sexual dimorphism.

The First Polycotylid Plesiosaur From Coniacian/Campanian Cretaceous Antarctica

First record of Polycotylidae (Sauropterygia, plesiosauria) from the Upper Cretaceous of Antarctica

Authors:

Novas et al

Abstract:

In the present paper we report the incomplete skeleton of an indeterminate polycotylid that includes the articulated pelvic girdle. The material was collected from the Alpha Member of the Santa Marta Formation (upper Coniacian–lower Campanian) on James Ross Island, Antarctic Peninsula. The specimen is referred to the Polycotylidae on the basis of its very elongate ischia and rimmed anterior and posterior articular surfaces of the dorsal vertebrae. Additionally, the caudal vertebrae show confluent parapophyses and neural arch facets. The present report constitutes the first record for polycotylids in Antarctica, being an important addition to the fossil marine reptile diversity. Polycotylids are a scarce component of the Weddellian herpetofauna, which are dominated by aristonectine and non–aristonectine elasmosaurids. In contrast, in Northern Hemisphere assemblages, polycotylids are an important component of the plesiosaur diversity. The scarcity of polycotylids may constitute another distinctive feature of Weddellian plesiosaur faunas.