Schizorhiza

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  and  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.

It lived in the Tethys Ocean between about 30° northern and southern latitude, and apparently was a successful species that ranged widely. Its fossils have been found in northern and central Africa, Iraq, Italy, Texas (United States), Coahuila (Mexico) and Bolivia. As its rostrum seems to be well-adapted for slashing and of little use for digging, it is presumed that this species did not share the whip-like tail of the bottom-dwelling relative Sclerorhynchus, but apart from the peculiar rostrum must have looked not too different from one of the sawfishes of today, regardless of whether they were very close relatives or not. Its total length was about 1.5 meters.

Its habitat was apparently shallow or epicontinental seas, as evidenced by its associated fauna, the cartilaginous fish Pseudocorax, Scapanorhynchus texanus and Serratolamna serrata, and the molluscs Cymprimera, Ethmocardium, Eutrephoceras, Platyceramus vanuxemi, Sphenodiscus and Turritella vertibroides.

See also

 Flora and fauna of the Maastrichtian stage
 List of prehistoric cartilaginous fish (Chondrichthyes)

Footnotes

References
  (2002): Schizorhiza: a unique sawfish paradigm from the Difunta Group, Coahuila, Mexico. Revista Mexicana de Ciencias Geológicas 19(1): 16-24 [English with Spanish abstract]. PDF fulltext

Category:Prehistoric fish of Africa
Category:Rays
Category:Prehistoric cartilaginous fish genera
Category:Cretaceous cartilaginous fish
Category:Fossil taxa described in 1930