Specimens of Omphalosaurus have been described from the western United States, Poland, Austria and the island of Spitsbergen off the northern coast of Norway.

Omphalosaurus is a moderately large and plump marine reptile,[2] measuring 5 m (16 ft) long and weighing more than 783 kg (1,726 lb).

The teeth are button-like, with a dome shape when viewed laterally and almost circular crowns[4] that have an irregular enamel surface akin to the texture of an orange peel.

[6] Jaw fragments have revealed that Omphalosaurus had a dental batteries that were optimized for constant wear, with high tooth replacement rates.

[7] Their teeth were optimized for heavy wear, and CT scans indicate they had high rates of replacement to deal with a hard diet.

Like ornithopods, Omphalosaurus have a high rate of tooth replacement and smooth secondary occlusal surfaces, but the lack of fibrous marine plants during the Middle Triassic make it unlikely that it was herbivorous.

Ammonites and pseudoplanctonic halobiid bivalves were, on the contrary, common in Omphalosaurus’ range and time period, and their shells were hard but thin.

Rothschild et al. attributed this to the lack of large aquatic predators in the early to middle Triassic, which meant that Omphalosaurus would not have needed to quickly dive to escape.

The ribs of Omphalosaurus share the dorsoventrally articulation of Ichthyosaurian family Shastasauridae and O. wolfi was shown to have the same cancellous bone structure as Ichthyosaurs, though this is common in several other aquatic species.

[7] One of the most distinct traits placing Omphalosaurus within Ichthyosauria is that they share the same microunit enamel in mature teeth that Ichthyosaurs are known to have, but that is rare in other reptiles.