Osteology and bone microstructure of new, small theropod dinosaur material from the early Late Cretaceous of Morocco

Abstract

The ‘Kem Kem beds’ of Morocco have yielded abundant material of large-bodied theropod dinosaurs, but remains of small theropod taxa are rare. Here, we describe two femora that provide additional information on the diversity of small-bodied theropods in the Gondwanan mid-Cretaceous. An almost complete femur (ROM 64666) represents a noasaurid theropod based on the presence of an elongate anteromedial flange that arises from the distal shaft and terminates proximal to the distal end of the bone; osteohistological analysis indicates that it was from a juvenile individual. It is possible that this femur represents a juvenile Deltadromeus, which is recovered as a putative noasaurid in some phylogenetic analyses. Nevertheless, as the affinities of Deltadromeus are debated, this femur currently represents the first definitive record of a noasaurid from northern Africa and one of the few records of this clade from the early Late Cretaceous. Moreover, if this specimen is not a juvenile Deltadromeus then it probably represents a new addition to the Kem Kem theropod assemblage. A second partial femur (ROM 65779) can be identified only as an indeterminate averostran theropod. It is similar in size to ROM 64666, but the presence of an external fundamental system (EFS) indicates that it pertained to a small-sized adult individual. These observations indicate that the two femora described herein are from different theropod taxa, thereby demonstrating that at least one additional small-bodied theropod taxon was present in the Kem Kem fauna, adding to the already high theropod species-richness of this unit.