Coelodus is an extinct genus of marine and possibly freshwater pycnodont fish. It contains only one definitive species, C. saturnus Heckel, 1854 (=C. rosthorni Heckel, 1854, C. suillus Heckel, 1854 ), from the Late Cretaceous (Turonian to Santonian) of Slovenia. Other species from the Late Jurassic to the Eocene have also been attributed to this genus based on isolated dental elements, but their assignment to Coelodus is uncertain, and this genus likely represents a non-monophyletic wastebasket taxon. A potential diagnostic trait is a prearticular tooth row with three regular highly elongated teeth.

Taxonomy

In addition to C. saturnus, the following are all dubiously classified into this genus: A number of former species in this genus based on complete fossil specimens, such as C. costae Heckel, 1856 (=C. achillis (Costa 1853), C. discus Heckel 1856 , C. grandis (Costa 1855) , C. pyrrhurus Heckel, 1854 ) C. subdiscus Wenz, 1989 , C. rosadoi Silva Santos, 1963 and C. toncoensis Benedetto & Sanchez ,1972 have since been reclassified into the genera Ocloedus and Costapycnodus, and many of these dentition-only taxa may belong there instead. Others, such as the former C. muensteri, are now placed in Anomoeodus. Indeterminate remains are known from the Csehbánya Formation of Hungary and the Kem Kem Beds of Morocco. Notably, these formations, in addition to other formations that Coelodus remains are known from worldwide, are freshwater deposits, suggesting at a potentially amphidromous lifestyle for Coelodus given its occurrence in marine environments as well. It is possible that freshwater and brackish environments served as refugia for Coelodus, allowing for it to survive the Cretaceous-Paleogene extinction event.