Elemgasem nubilus: a new brachyrostran abelisaurid (Theropoda, Ceratosauria) from the Portezuelo Formation (Upper Cretaceous) of Patagonia, Argentina

Abstract

Abelisaurids are medium-large-sized theropod dinosaurs that were predominant in the carnivorous fauna during the Late Cretaceous of Gondwana. These predators are abundant in the Cretaceous fossil strata of Patagonia, which yield the best record for this group. In the Late Cretaceous, abelisaurids appear in almost all regions of Gondwana and in all stages, except for the Coniacian, in which they are globally unknown. Here we describe a new abelisaurid, Elemgasem nubilus gen. et sp. nov., from the Portezuelo Formation (Turonian-Coniacian), Patagonia, Argentina. The palaeohistology of the appendicular bones of Elemgasem shows that the holotype was a subadult individual, but had achieved sexual maturity. This taxon is based on several axial and appendicular elements, and is diagnosed by the presence of a marked pattern of rugosity on the lateral surface of the fibula and a dorsoventrally deep lateral wall of the calcaneum. Moreover, the posterior caudal vertebrae have a morphology slightly different from any other abelisaurid. Elemgasem nubilus is recovered as an unstable taxon within Brachyrostra, given that it was recovered as sister taxon of Furileusauria or in several positions within this clade. Despite the problematic phylogenetic relationships of Elemgasem nubilus, it is important because it is the first abelisaurid from the Turonian-Coniacian interval and it increases the diversity of this theropod family at a time of marked turnover in the tetrapod fauna of South America, global climate change, and mass extinction events recorded worldwide in the marine realm.

Una Vértebra Caudal No Furileusauriana De La Formación Bajo De La Carpa (Santonian) Y Variación Morfológica en La Cola De Los Abelisauridae

“…In particular, the stratigraphic record of abelisaurids encompasses all Patagonian Upper Cretaceous basins in which continental rocks are preserved (e.g., Neuquén Basin, Somuncura-Cañadón Asfalto Basin, Golfo San Jorge Basin, and Austral Basin). The knowledge of this family of theropods concerning their anatomy, evolutionary history, and phylogenetic relationships has increased notably in recent decades, with the Patagonian records providing the most novel information due to the abundance and diversity of the group to date (e.g., Bonaparte, 1985;Bonaparte & Novas, 1985;Bonaparte et al, 1990;Coria & Salgado, 1998;Coria et al, 2002;Calvo et al, 2004;Canale et al, 2009;Novas et al, 2013;Gianechini et al, 2015Gianechini et al, , 2021Filippi et al, 2016Filippi et al, , 2018bMéndez et al, 2018Méndez et al, , 2022Cerroni & Paulina-Carabajal, 2019;Cerroni et al, 2020;Aranciaga-Rolando et al, 2021;Baiano et al, 2021Baiano et al, , 2022.…”