Choristodera

Lore & Background

A year later, Paul Gervais described Simoedosaurus from Upper Paleocene deposits in France. For over a century, these remained the only recognized choristoderes. In the late 20th century, new taxa were described from Lower Cretaceous sediments in Mongolia by Soviet-Mongolian teams, and Susan E. Evans described new material of Cteniogenys from the Middle Jurassic of Britain, revealing it to be a small, lizard-like choristodere.

Reader's Guide

Choristoderes are significant for their long temporal range and morphological diversity, offering insights into the evolution of semiaquatic reptiles in the Northern Hemisphere. They are generally thought to be derived neodiapsids close to or within Sauria. The group includes both crocodile-like neochoristoderes and smaller lizard-like forms, with some long-necked species resembling plesiosaurs. Their fossils are exclusively found in freshwater deposits, often alongside turtles, fish, and crocodyliformes, suggesting a warm temperate climate preference. The discovery of skin impressions and soft tissue in some specimens provides rare details about their integument and aquatic adaptations. Choristoderes likely occupied distinct ecological niches, with neochoristoderes coexisting with blunt-snouted crocodyliformes but not narrow-snouted ones.

Did You Know?

• Choristoderes possess a unique skull bone not found in other reptiles, called the neomorphic bone.
• The largest known choristodere, Kosmodraco dakotensis, reached an estimated length of about 5 m.
• Champsosaurus had a heart-shaped skull when viewed from above due to expanded temporal fenestrae.
• Some choristoderes, like Hyphalosaurus, had webbed feet and a tail fin for swimming.