Sigilmassasaurus is Spinosaurus: A reappraisal of African spinosaurines

Abstract

Remains of enigmatic spinosaurs from mid-Cretaceous North African strata have, for over a century, been the subject of taxonomic deliberations. The gigantic Spinosaurus aegyptiacus Stromer, 1915 has gained iconic status in the vertebrate palaeontological community and amongst the general public. Perhaps the largest predatory dinosaur to have lived, this animal exhibits a bizarre range of adaptations consistent with a piscivorous diet and semiaquatic mode of life. Despite its popularity, the systematics of this taxon remains a matter of considerable debate. African spinosaur taxonomy is complex, with up to three separate species proposed for the Cretaceous Kem Kem Group of Morocco: Spinosaurus aegyptiacus, Spinosaurus maroccanus Russell, 1996 and Sigilmassasaurus brevicollis Russell, 1996.Here, the taxonomic status of spinosaurs in the Kem Kem Group is examined, and the morphology of the cervical and dorsal vertebrae re-evaluated in the light of this taxonomic reappraisal.The validity of Spinosaurus maroccanus and Sigilmassasaurus brevicollis are not supported, as all autapomorphies of these taxa are proposed here to be the result of intraspecific variation, or morphological changes through the axial column of a single taxon. Both taxa are junior synonyms of Spinosaurus aegyptiacus.This reanalysis has implications for the taxonomy of spinosaurs from other deposits. Based on the currently available material, the Brazilian spinosaurid Oxalaia quilombensis is determined to fall within the Spinosaurus aegyptiacus hypodigm. The prevalence of spinosaurid heterodonty and limited diagnostic potential of spinosaur teeth necessitates that two spinosaurid tooth taxa: Ostafrikasaurus crassiserratus and Siamosaurus suteethorni, be regarded nomina dubia.