Polycotylids are a clade of relatively small-bodied, typically snort-necked, long-snouted plesiosauroids, from the Cretaceous Period.
They were traditionally classified as pliosaurs because of their short necks and relatively large heads. However, cladistic analyses taking into account a broader suite of anatomical characters have shown they are plesiosauroids, more closely related to long-necked elasmosaurids and cryptoclidids than to pliosaurs. The discovery of a relatively long-necked polycotylid, Serpentisuchops, in 2022 (Persons et al. 2022) showed that polycotylids had a greater diversity of body plans than previously thought.
All polycotylids share a number of features including an elongate rostrum and a short postorbital region. They had a worldwide distribution in the Cretaceous Period.
Classification
Polycotylids form a sister relationship with leptocleidids, together forming the clade Leptocleidia. Some classifications further divide dirived polycotylids into two subfamilies, the Palmulainae and the Polycotylinae.
Phylogeny
After Persons et al. (2022)
Polycotylid genera
Thililua
Thililua has 30 cervical vertebrae. Each cervical has a longitudinal ridge on its lateral surfaces, this is a convergent feature with elasmosaurids. The skull of Thililua is relatively large with a short postorbital region and elongate rostrum. The type specimen (MHNGr.PA.11710) consists of a complete skull, entire cervical and pectoral series, and the first four […]
Polycotylus
Polycotylus latipinnis was the first short-necked plesiosaur to be recognised in North America (Carpenter 1996), and the first polycotylid to be described and named (Cope 1869). It was established in the same volume that coined the name Elasmosaurus and contained the infamous ‘head on the wrong end’ reconstruction (Cope 1869). However, despite their equally long […]
Genera not yet added to the directory:
- Dolichorhynchops
- Eopolycotylus
- Georgiasaurus
- Pahasapasaurus
- Palmulina
- Sulcusuchus
- Trinacromerum
- Martinectes