Morphofunctional Analysis of the Quadrate of Spinosauridae (Dinosauria: Theropoda) and the Presence of Spinosaurus and a Second Spinosaurine Taxon in the Cenomanian of North Africa.

Christophe Hendrickx,Eric Buffetaut,Octávio Mateus,Alistair Robert Evans

doi:10.1371/journal.pone.0144695

Abstract

Six quadrate bones, of which two almost certainly come from the Kem Kem beds (Cenomanian, Upper Cretaceous) of south-eastern Morocco, are determined to be from juvenile and adult individuals of Spinosaurinae based on phylogenetic, geometric morphometric, and phylogenetic morphometric analyses. Their morphology indicates two morphotypes evidencing the presence of two spinosaurine taxa ascribed to Spinosaurus aegyptiacus and? Sigilmassasaurus brevicollis in the Cenomanian of North Africa, casting doubt on the accuracy of some recent skeletal reconstructions which may be based on elements from several distinct species. Morphofunctional analysis of the mandibular articulation of the quadrate has shown that the jaw mechanics was peculiar in Spinosauridae. In mature spinosaurids, the posterior parts of the two mandibular rami displaced laterally when the jaw was depressed due to a lateromedially oriented intercondylar sulcus of the quadrate. Such lateral movement of the mandibular ramus was possible due to a movable mandibular symphysis in spinosaurids, allowing the pharynx to be widened. Similar jaw mechanics also occur in some pterosaurs and living pelecanids which are both adapted to capture and swallow large prey items. Spinosauridae, which were engaged, at least partially, in a piscivorous lifestyle, were able to consume large fish and may have occasionally fed on other prey such as pterosaurs and juvenile dinosaurs.

Highlights

The Kem Kem region of south-eastern Morocco is very well known for its rich vertebrate assemblage of Cenomanian age, which is characterized by a high diversity of predatory dinosaurs [1,2,3,4,5,6,7,8,9]
Because Muséum d’Histoire Naturelle of Marrakech (MHNM).KK374,.KK375 and.KK377 were bought in local markets in Erfoud (Escuillié pers. comm.) and given the fact that the sediment adhering to them is consistent with the lithology of the Kem Kem beds in color, composition, and texture, it is unlikely that these specimens come from another lithostratigraphic unit of North Africa
MHNM.KK374 (Fig 3A–3F) is a left quadrate of small size displaying ontogenetic features typical of immature theropods so that the bone can confidently be ascribed to a juvenile individual

Summary

Introduction

The Kem Kem region of south-eastern Morocco is very well known for its rich vertebrate assemblage of Cenomanian age, which is characterized by a high diversity of predatory dinosaurs [1,2,3,4,5,6,7,8,9]. The presence of at least five non-avian theropod clades has been documented in the Kem Kem beds, hitherto including non-abelisaurid Ceratosauria (Noasauridae?), Abelisauridae, Spinosauridae, Carcharodontosauridae, and Dromaeosauridae. Material resembling the primitive ceratosaur Elaphrosaurus was already reported by Lavocat [16], and additional remains of noasaurids have been recently described and may belong to a juvenile individual of Deltadromeus [1]. Sigilmassasaurus brevicollis, coined by Russell [2] and initially classified to the new clade Sigilmassasauridae, was interpreted as belonging to Carcharodontosaurus saharicus [5,23,25] (an hypothesis rejected by Novas et al [26]), Spinosaurus maroccanus [11], and recently to Spinosaurus aegyptiacus [22]. Dromaeosauridae, the only known non-avian coelurosaurs from the Kem Kem beds, have so far been documented by isolated teeth [9,28]. To be present in the Kem Kem beds alongside non-avian dinosaurs [5]

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