Comparative taphonomy of Kem Kem Group (Cretaceous) pterosaurs of southeast Morocco

Abstract

Although diverse, disparate, widespread, and long-lived, our understanding of pterosaurs is heavily biased by specimens from Konservat-Lagerstätten. Here we consider the pterosaur assemblage of the mid-Cretaceous Kem Kem Group of southeast Morocco and compare its taphonomy to other Cretaceous pterosaur-bearing assemblages. The Kem Kem Group pterosaur bones are usually fragmentary and isolated but preserved three-dimensionally, with excellent preservation of macroscopic internal structures and bone histology at ultrastructural levels. The pterosaur assemblage is dominated by azhdarchoid jaw fragments, all anterior of the nasoantorbital fenestra and divergence of the mandibular rami. Post-cranial elements are much rarer with a striking lack of syncarpals, despite being some of the most robust elements of the skeleton. Comparisons with similar deposits in the United Kingdom, Uzbekistan and USA suggest that this relative skeletal abundance is unusual for pterosaur assemblages. The overabundance of jaw material in the Kem Kem Group is likely the result of a combination of factors including the inherent mechanical strength of the jaws, selective predation and scavenging and transportation/hydrodynamic sorting of some elements. The Kem Kem Group should be considered a Konzentrat-Lagerstätte due to the high abundance of vertebrate material. Despite the fragmentary nature of the material, it has excellent preservation of internal structures at macroscopic and microscopic scales. The Kem Kem Group pterosaur assemblage is among the most species diverse known, but taphonomic processes and biases likely obscure its true diversity.