Contrasting preservation in pycnodont fishes reveals first record of regurgitalites from the Upper Cretaceous (Maastrichtian) Moroccan phosphate deposits

Isolated jaw elements (vomers, prearticulars, premaxillae) of pycnodont fishes (Actinopterygii: Pycnodontiformes) occur frequently within the Moroccan Oulad Abdoun phosphate assemblages, although their taphonomy has remained unstudied. Recent collecting has identified two conflicting taphonomies: unetched (unaltered) and etched. Three etched jaw specimens of Phacodus punctatus Dixon, 1850 display severe pitting, corrosive marking and enamel discolouration characteristics on the bone and teeth, strongly inferring them to be regurgitalites. Regurgitalites are fossilised remains of partial or undigested skeletal elements that have been ejected from the mouth of the producer. Taphonomy of these etched specimens is attributed to partial transport through the gut of a larger vertebrate where they were partially digested before being regurgitated orally. Different macropredators in the assemblage are scored on their physiological capabilities of being the producer, with a large mosasaur like Prognathodon being the most plausible culprit. Regurgitalites are previously unreported in the formation, further adding to our understanding of the complex trophic food webs in the latest Cretaceous of Morocco. The elusive form and function of the characteristic dental ‘pits’ in the genus Phacodus are additionally investigated using thin section petrography and scanning electron microscopy (SEM).