Trachelosauridae

Trachelosauridae (also known as Dinocephalosauridae) is an extinct clade of archosauromorph reptiles that lived throughout the Triassic period. Like their close relatives the tanystropheids, they were "protorosaur"-grade archosauromorphs characterized by their long necks. Unlike tanystropheids, which lengthen their neck primarily by elongating the individual cervical (neck) vertebrae, trachelosaurids achieved their long necks by the addition of more vertebrae. The most extreme example of this trend was Dinocephalosaurus, which had at least 32 vertebrae in the neck alone, far more than the 13 neck vertebrae of Tanystropheus.

Trachelosaurids are known from Europe (Poland, Germany, Austria, Netherlands) and China. Some members of the family (i.e. Dinocephalosaurus) were solely marine animals with paddle-like limbs, inhabiting the coastlines of the Tethys Ocean. Dinocephalosaurus was so specialized for aquatic life that it evolved to be viviparous (live-bearing), the only undisputed example of an archosauromorph adapted for live birth. Other members (i.e. Pectodens) were better suited for terrestrial life, suggesting wide ecological diversity in just the few known species in this family.