New mid-cervical vertebral morphotype of Spinosauridae from the Kem Kem Group of Morocco

Bradley Mcfeeters

doi:10.18435/vamp29370

Abstract

An unusual mid-cervical vertebra belonging to a large spinosaurid from the Cenomanian Kem Kem Group of Morocco is described. It is compared to the characteristic morphology of each reconstructed cervical position in Spinosaurus aegyptiacus, based on a recent composite reconstruction that incorporates most previously referred material from this unit. Rather than conforming to any of the previously identified cervical positions in its morphology, the specimen displays a unique combination of mid-cervical characters, with the relatively compact centrum suggesting a position as C4, and the form of the neural arch laminae suggesting a position as C5 or C6. Furthermore, it displays two characters that are previously unknown in spinosaurid mid-cervicals from the Kem Kem Group: a rounded hypapophyseal tuberosity that is not continuous with a ventral keel, and a moderately developed, dorsally oriented epipophysis that does not overhang the postzygapophysis posteriorly. The diagnostic value of positionally variable cervical vertebral characters in spinosaurid systematics is discussed. Although limited, the new data could lend support to the controversial hypothesis that two spinosaurid taxa are represented in the Kem Kem Group.

Highlights

Spinosauridae is a clade of large, specialized tetanuran theropods that was widely distributed during the Cretaceous (Hone and Holtz 2017)
This specimen offers further opportunity to test the proposed characterizations of individual axial positions that make up the composite reconstructed neck of Spinosaurus aegyptiacus (Smyth et al 2020), and the hypothesis that all spinosaurid material from the Kem Kem Group is referable to a single species
The specimen ROM 65537 represents a new spinosaurid mid-cervical morphotype from the Kem Kem Group of Morocco, with a unique combination of characters not previously documented in a single element

Summary

INTRODUCTION

Spinosauridae is a clade of large, specialized tetanuran theropods that was widely distributed during the Cretaceous (Hone and Holtz 2017). Most recently, Smyth et al (2020) reevaluated the taxonomy of the Kem Kem Group spinosaurids and concluded that the recognition of only a single taxon, Spinosaurus aegyptiacus, was justified They produced a revised reconstruction of the post-atlas cervical and anterior dorsal vertebral series of Spinosaurus aegyptiacus, with the known fossil material representing an essentially complete sampling of axial positions C2–D3 (second cervical to third dorsal) in this taxon. I describe a cervical vertebra of a spinosaurid from the Kem Kem Group exhibiting an unusual combination of positionally variable characters This specimen offers further opportunity to test the proposed characterizations of individual axial positions that make up the composite reconstructed neck of Spinosaurus aegyptiacus (Smyth et al 2020), and the hypothesis that all spinosaurid material from the Kem Kem Group is referable to a single species

MATERIALS AND METHODS

CONCLUSIONS