Schizorhiza

Schizorhiza Temporal range: Late Cretaceous, 83.6–66 Ma PreꞒ Ꞓ O S D C P T J K Pg N Campanian-Maastrichtian
Restoration
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Order:	Rajiformes
Suborder:	†Sclerorhynchoidei
Family:	†Schizorhizidae Kirkland & Aguillón-Martínez, 2002
Genus:	†Schizorhiza Weiler, 1930
Binomial name
†Schizorhiza stromeri Weiler, 1930
Synonyms
Schizorhiza weileri Serra, 1933

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. Like other sawfish-like rays from the Mesozoic, 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.^[1]

Taxonomy[]

Due to its unique rostral teeth, Schizorhiza is placed in the monotypic subfamily Schizorhizinae. Despite formerly being classified within a family of extinct sawfish-like rays known as Sclerorhynchidae,^[2] phylogenetic analyses indicate that Ischyrhiza, Schizorhiza, and Onchopristis form a distinct clade that groups closer with the extant family Rajidae, which contains the true skates, possibly rendering the suborder Sclerorhynchoidei paraphyletic.^[3]

Naming[]

Schizorhiza was named in 1930 by W. Weiler.^[4] Weiler added the epithet stromeri, which honours Ernst Stromer. In 1933, Serra named the second species, S. weileri.^[5] It was seen as a synonym of the type species as early as 1940 by Camille Arambourg.^[6] It was made a junior synonym in by Welton & Farish in 1993.^[7]

Description[]

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 Sclerorhynchidae, 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.^[1]

Paleoecology[]

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 similar, bottom-dwelling 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.^[1]

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 , , Eutrephoceras, Platyceramus vanuxemi, Sphenodiscus and Turritella vertibroides.^[1]

See also[]

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

References[]