Polycotylidae

Polycotylidae is an extinct family of short-necked plesiosaurs with elongated snouts, known from marine deposits of the Cretaceous Period.

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Plesiosauria: An order of extinct marine reptiles with four flippers and bodies adapted for swimming. Polycotylids are plesiosaurs, despite their unusually short necks.
Plesiosaur locomotion: The swimming mechanics of plesiosaurs, which used four limbs as underwater flight surfaces. This broad propulsion model frames how polycotylids moved through marine habitats.
Polycotylus: A genus of Cretaceous polycotylid plesiosaurs known from North America. This genus gives the family its name and anchors its fossil record.
Cretaceous: A geologic period lasting from about 145 to 66 million years ago. Polycotylids lived during this period's changing marine ecosystems.
Elasmosauridae: An extinct family of plesiosaurs characterized by exceptionally long necks and small heads. Elasmosaurids contrast sharply with polycotylids' short necks and long snouts.
Plesiosaur neck evolution: The evolutionary variation in neck length among plesiosaurs. Polycotylids represent the short-necked end of plesiosaur diversity.
Thalassophonea: A clade of plesiosaurs that includes polycotylids and many other short-necked forms. Polycotylids are members of this short-necked plesiosaur clade.
Dolichorhynchops: A genus of Cretaceous polycotylid plesiosaurs known from marine deposits in North America. Its fossils illustrate the group's long snout and short-necked body plan.
Early Cretaceous: The first epoch of the Cretaceous Period, lasting about 145 to 100 million years ago. Some early members establish the family's presence before its later diversity.
Pliosauridae: An extinct family of short-necked plesiosaurs, often with large skulls and powerful jaws. Pliosaurids share short necks but differ in skull proportions and ancestry.