Choristodera

Choristodera is an extinct clade of aquatic and semiaquatic reptiles that lived from the Mesozoic into the Miocene. Its members included long-snouted forms resembling crocodiles.

Diapsid: A reptile whose skull ancestrally has two openings behind each eye socket. Choristoderes are generally placed among diapsid reptiles, though their exact relationships remain debated.
Pachyostosis: The unusually thick, dense growth of bone, often associated with buoyancy control in aquatic vertebrates. Some choristoderes had dense limb bones that may have helped stabilize them in water.
Champsosaurus: A long-snouted neochoristodere known from Cretaceous and Paleogene deposits in North America and Europe. Its abundant fossils document the classic crocodile-like choristodere form.
Mesozoic: The geological era spanning the Triassic, Jurassic, and Cretaceous periods, about 252 to 66 million years ago. Choristoderes first appear in the Mesozoic fossil record.
Phylogenetic uncertainty: The difficulty of resolving evolutionary relationships when evidence is incomplete or supports competing trees. Different analyses place Choristodera differently among reptile lineages.
Archosauromorpha: A major reptile lineage that includes archosaurs and several extinct groups more closely related to them than to lepidosaurs. Some analyses place choristoderes within this broad reptile lineage.
Aquatic locomotion: Movement through water using limbs, body undulation, or specialized fins and tails. Choristodere skeletons preserve clues to how different forms moved through aquatic habitats.
Hyphalosaurus: A small-bodied choristodere from the Early Cretaceous Jehol Biota of China. Its fossils show a slender aquatic form distinct from large-snouted neochoristoderes.
Miocene: An epoch of the Neogene Period lasting from about 23 to 5.3 million years ago. Choristodere fossils extend into the Miocene, long after most other non-avian reptile groups declined.
Fossil record: The preserved and discovered remains of organisms across geological time. Uneven preservation leaves major gaps in choristodere diversity and evolutionary history.

Linked from 1 page