Schizorhiza: a unique sawfish paradigm from the Difunta Group, Coahuila, Mexico

Abstract

The sclerorhynchid sawfish Schizorhiza is widespread in Upper Cretaceous marine strata of the Difunta Group of Coahuila, Mexico ranging from the latest Campanian to latest Maastrichtian. A fragmentary rostrum from the latest Campanian Cerro de Pueblo Formation provides significant new information about this sawfish.

The rostrum of Schizorhiza is similar to that of other known Sclerorhynchidae species in its gradual taper and in that superficial ophthalmic nerves run down the dorsal grooves and the buccopharyngeal nerves run down the ventral grooves. Unlike other scelerorhynchids, it was discovered that the distinctive diamond shaped rostral teeth with their flaring roots were not shed with the addition of alternating replacement teeth. This results in Schizorhiza small teeth being densely packed into files to produce a continuous, sharp, serrated edge down each side of a rostrum that is more than 50 cm in length. This rostral tooth pattern is unique among the Sclerorhynchoidea and indicates that rather than probing for food in soft sediments with a comb-like rostrum as other sawfish, Schizorhiza specialized in hunting fish with its truly saw-like rostrum.