Polycotylids have been traditionally classified as pliosaurs because of their short necks and relatively large heads. However, cladistic analyses that take into account a broader suite of anatomical characters have revealed that they are probably plesiosauroids, and therefore more closely related to the long-necked elasmosaurids and cryptoclidids than to pliosaurs.

Dolichorhynchops bonneri

All polycotylids share a number of features including an elongate rostrum and short postorbital region. They had a worldwide distribution in the Cretaceous Period.

Polycotylid genera


Edgarosaurus is a basal polycotylid (Druckenmiller 2002) from the Thermopolis Shale


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.


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).

Genera not yet added to the directory:

  • Dolichorhynchops
  • Eopolycotylus
  • Georgiasaurus
  • Umoonasaurus
  • Pahasapasaurus
  • Palmulina
  • Sulcusuchus
  • Trinacromerum