Schizorhiza

Schizorhiza weileri

Schizorhiza is a fossil genus of cartilaginous fish, containing a single accepted species Schizorhiza stromeri. Its fossils are found in rocks dating from the Campanian and Maastrichtian stages; it thus lived between about 83.6 and 66 million years ago. Its Mesozoic suborder, the Sclerorhynchoidea, cannot be unequivocally assigned to the Rajiformes (skate and ray) or to the Pristiformes (sawfish) order. Due to its unique rostral teeth, Schizorhiza is placed in the monotypic subfamily Schizorhizinae. Like all Sclerorhynchoidea, it probably did not survive the Cretaceous–Paleogene extinction event; there are a few remains from the Paleogene but these seem to have been reworked from Late Cretaceous deposits.

Schizorhiza is unique among all "saw-snouted" Elasmobranchii in that its rostral teeth did not fall off as they are replaced. Rather, they remain in place, with the new teeth under them, until they are worn off. Thus, the rostrum's edge had a continuous serrated cover of tooth enamel. Full-grown rostral teeth measured less than in other Sclerorhynchoidea, let alone sawfishes, at 1–2 cm tall and 4–8 mm wide. They had a small triangular or rhomboidal shape at the tip, with sharp cutting edges, and a long forked peduncle, each lobe of which divides into four lobelets proximally. The new teeth developed inside the peduncular fork; the scientific name Schizorhiza – meaning "split root" – refers to the shape of the rostral teeth. The oral teeth were very small (about 1.5-2.5 mm high and 1–2 mm wide), with a large and recurved central point and keels at the side that formed tiny secondary points.