Choristodera

Lore & Background

For over a century, Champsosaurus remained the only recognized choristodere. In the late 20th century, new taxa were described from Lower Cretaceous sediments in Mongolia by Soviet-Mongolian teams, and Susan E. Evans reidentified Cteniogenys from the Middle Jurassic of Britain as a small, lizard-like choristodere.

Reader's Guide

Choristoderes are significant for understanding the evolution of semiaquatic reptiles in the Northern Hemisphere. Their morphological diversity—from crocodile-like neochoristoderes to lizard-like and long-necked forms—illustrates adaptive radiation in freshwater environments. The group's long temporal range, from the Jurassic to the Miocene, and its presence in warm temperate climates, including the high Arctic during a period of extreme warmth, provide insights into past ecosystems and climate. The discovery of a novel skull bone (the neomorph) and shared skeletal traits help define the order. Their apparent niche differentiation with crocodyliformes suggests they occupied distinct ecological roles, with gharial-like neochoristoderes coexisting with blunt-snouted crocodyliformes but not narrow-snouted ones. The preservation of skin impressions and webbed feet in some species indicates adaptations for aquatic life.

Did You Know?

• Choristoderes are named from Greek words meaning 'separated neck'.
• The smallest choristoderes, like Cteniogenys and Lazarussuchus, were only about 30 cm long, while the largest, Kosmodraco dakotensis, reached about 5 m.
• Choristoderes possess a unique skull bone called the neomorph, not found in other reptiles.
• Skin impressions of Champsosaurus show small pustulate and rhomboid scales, with no osteoderms.

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