A new species of longirostrine plioplatecarpine mosasaur (Squamata: Mosasauridae) from the Late Cretaceous of Morocco, with a re-evaluation of the problematic taxon ‘<i>Platecarpus</i>’ <i>ptychodon</i>

The Upper Cretaceous phosphates of Morocco preserve one of the world’s most diverse assemblages of mosasaurs, reflecting the adaptive radiation of this clade during the Maastrichtian. Herein, we describe a new mosasaur from these deposits. Although the teeth of this specimen resemble those of ‘<i>Platecarpus</i>’ <i>ptychodon</i>, suggesting referral to this species, we re-examine and ultimately reject the fundamental validity of ‘<i>P.</i>’ <i>ptychodon</i> due to the non-diagnostic nature of its holotype and original diagnosis. We instead designate the new specimen as the holotype of a new genus and species, <i>Gavialimimus almaghribensis</i>, gen. et sp. nov. <i>G. almaghribensis</i> is characterized by a highly elongate snout, highly retracted nares and large supratemporal fenestrae, among other features. Phylogenetic analysis under multiple parsimony-based methods reveals novel substructure within the subfamily Plioplatecarpinae, consistently recovering a clade uniting the new species with <i>Selmasaurus</i> and the enigmatic <i>Goronyosaurus</i>. Synapomorphies of this clade include a highly constricted parietal, with <i>Selmasaurus</i> and <i>Gavialimimus</i> being further united by a broadly excavated medial surface of the quadrate suprastapedial process. The cranial morphology of <i>G. almaghribensis</i> also provides new insight into several aspects of mosasaur evolution and comparative anatomy, including adaptive radiation and niche partitioning in Moroccan marine palaeoecosystems. http://zoobank.org/urn:lsid:zoobank.org:pub:6896D6EE-2609-4917-A811-904B5AA7A8BB