Polycotylidae

Polycotylidae is a family of plesiosaurs from the Cretaceous, a sister group to Leptocleididae. They are known as false pliosaurs. Polycotylids first appeared during the Albian stage of the Early Cretaceous, before becoming abundant and widespread during the early Late Cretaceous. Several species survived into the final stage of the Cretaceous, the early Maastrichtian around 72 million years ago.^[3] The possible latest surviving member Rarosaurus from the late Maastrichtian is more likely a crocodylomorph.^[4]

Polycotylids Temporal range: Early - Late Cretaceous, 113–72 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Martinectes in the Rocky Mountain Dinosaur Resource Center
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	†Sauropterygia
Order:	†Plesiosauria
Clade:	†Leptocleidia
Family:	†Polycotylidae Williston, 1909
Genera
†Edgarosaurus †Manemergus †Mauriciosaurus †Piratosaurus? †Rarosaurus? †Thililua †Occultonectia[1] †Plesiopleurodon †Sulcusuchus †Palmulasaurinae †Pahasapasaurus †Palmulasaurus †Polycotylinae †Eopolycotylus †Georgiasaurus †Polycotylus †Scalamagnus †Serpentisuchops †Trinacromerum †Dolichorhynchia[2] †Dolichorhynchops †Martinectes †Unktaheela

With their short necks and large elongated heads, they resemble the pliosaurs, but closer phylogenetic studies indicate that they share many common features with the Leptocleididae and Elasmosauridae. They have been found worldwide, with specimens reported from New Zealand, Australia, Japan, Morocco, the US, Canada, Eastern Europe, and South America.^[5]

Phylogeny

Trinacromerum bentonianum from the Late Cretaceous of Kansas

Cladogram after Albright, Gillette and Titus (2007).^[6]

Plesiosauria	Plesiosaurus Tricleidus Polycotylidae Edgarosaurus Thililua Palmulainae UMUT MV 19965 (from Japan) Pahasapasaurus (=AMM 98.1.1)[7] Palmulasaurus Polycotylinae Dolichorhynchops Trinacromerum Eopolycotylus Polycotylus

Cladogram after Ketchum and Benson (2010).^[8]

Plesiosauroidea	Cryptoclididae Leptocleidia Leptocleididae Polycotylidae Plesiopleurodon Edgarosaurus QM F18041 Eopolycotylus Trinacromerum Dolichorhynchops herschelensis Dolichorhynchops Manemergus Palmulasaurus

Below is a cladogram of polycotylid relationships from Ketchum & Benson, 2011.^[9]

Plesiosauroidea	Cryptoclididae Leptocleidia Leptocleididae Polycotylidae Edgarosaurus Plesiopleurodon QM F18041 Eopolycotylus Polycotylus Thililua Trinacromerum Manemergus Dolichorhynchops herschelensis Dolichorhynchops Palmulasaurus