Onchopristis is an ischyrhizid sclerorhynchiform cartilaginous fish from the Early-Late Cretaceous of the entire world. It was officially named in 1917 by Ernst Stromer. It was one of the most widespread saw-nosed rays during the Cretaceous, as well as one of the most successful.
Physiology[]
Onchopristis resembled modern sawfish. It was a fish with a flat, shark-like body, triangular pectoral (arm) and dorsal (back) fins, a crescent-shaped, upwards-pointing caudal (tail) fin, small jaws just on the underside of its mid-sized head, eyes on the top of its head, 5 gills located on each corner of its head's underside, and a flat, long, barbed rostrum that extended from the tip of its head. Its body would have been covered in scaly skin, with a row of thorn-like bumps running down its back.
Diet[]
Onchopristis was a predator, preying on smaller fish, crustaceans, and mollusks. Its small and blunt teeth were used to get a hold of prey, and its large, saw-like rostrum was used to either swipe at prey to knock them out or pin them down as it ate them.
Ecology[]
Onchopristis was quite similar to modern sawfish; it had an elongated, barbed rostrum that it used to detect and catch prey. Its head and rostrum contained thousands of sensory organs that it used to detect movements in the water, allowing to find prey in the murky waters it likely swam through; once it spotted a prey item, it would either use its rostrum to incapacitate the prey item by swiping at it or pin it against the seafloor or riverbed as the large ray ate it up. However, despite its large size, it would have fallen prey to larger predators such as Spinosaurus; due to this, its eyes were positioned on the top of its head so that it could detect predators swimming above it, and, unlike modern sawfish, its back was covered in a row of thorny spines in order to stop predators from effortlessly biting into it (similarly to thornback rays). As is the case with modern sawfish, Onchopristis would have mainly lived in coastal and estuarine waters, but, due to its presumed ability to adapt to various salinities, would have been able to live in a freshwater environment; in fact, it is somewhat likely that it would have been anadromous (migrating into freshwater in order to breed), and that juveniles would have spent the first years of their life in freshwater environments before moving into saltier waters in adulthood.
In popular culture[]
Onchopristis was featured in the 1st episode of the 2011 documentary Planet Dinosaur, where it is shown as an anadromous fish that migrates into the freshwater rivers of Cretaceous North Africa to breed. In the episode itself, a school of the saw-nosed rays migrate the freshwater rivers; a Spinosaurus takes advantage of this migration and hunts a few of them, eats a few large chunks of flesh from their bodies, and then leaves the rest to scavengers like Rugops.