Elemgasem nubilus. Image credit: Abel Germán Montes
Abelisauroidea is the best known carnivorous dinosaur group from Gondwana. The clade was erected by the legendary paleontologist Jose Bonaparte with the description of Abelisaurus Comahuensis. These ceratosaurian theropods are medium to large, robust animals, such as the Carnotaurus and the Majungasaurus of Madagascar. The group exhibits short, round snouts; thickened teeth; short, stocky arms; and highly reduced forearms.
The Cretaceous beds of Patagonia holds an extraordinary record of abelisaurids, although there is a paucity during the whole Coniacian. This lack of specimens during this interval is a worldwide phenomenon. Thus, the Late Cretaceous record of abelisaurids is represented by two intervals: the Cenomanian–Turonian, with taxa from Argentina, Africa and Madagascar, and the Santonian–Maastrichtian, with taxa from Argentina, Brazil, Africa, Madagascar and India. Elemgasem nubilus, from the Portezuelo Formation of Argentina, is the first abelisaurid from the Turonian–Coniacian interval. The new specimen increases the diversity of this clade at a time of significant turnover in the tetrapod fauna of South America, marked by global climate change, and mass extinction events recorded worldwide in the marine realm.
Femur histology of Elemgasem nubilus. From Baiano et al., 2022.
The holotype (MCF-PVPH-380), discovered in 2002, includes several axial and appendicular elements, and exhibits the following features: a marked rugosity on the lateral surface of the fibula, a high lateral surface and a high proximolateral wall of the calcaneum, as well as posterior caudal centra with oval articular surfaces and a groove on the ventral surface. Osteohistological analysis of the femur and phalanx III-2 indicates that this new specimen was at least 8 year old and had achieved sexual maturity but was still growing.
Elemgasem measured about 4 meters (13 feet) long. The genus name refers to the Tehuelche god Elemgasem, the ‘owner’ of the animals and founder of the northern Tehuelche people. The specific name nubilus comes from the Latin ‘foggy days’ in reference to the climatic conditions during the palaeontological expedition when this specimen was discovered.
Location map and geological strata from which the specimen Elemgasem nubilus MCF-PVPH-380 holotype was recovered. From Baiano et al., 2022.
In the Late Cretaceous Abelisauridae splits in the clade Majungasaurinae and and the clade Brachyrostra. Post-Coniacian brachyrostrans constitute a natural group, Furileusauria. Phylogenetic analysis recovered Elemgasem as an unstable taxon, occupying all possible positions within Furileusauria, or as a sister taxon of this clade.
Elemgasem nubilus lived about 90 million years ago in one of the most phylogenetically diverse fauna from the middle Late Cretaceous of South America, which includes crocodiles, pterosaurs, ornithopods, and four distinct lineages of tetanuran theropods, such as Megaraptor, the alvarezsaurid Patagonykus, the dromaeosaurids Neuquenraptor, Pamparaptor and Unenlagia, and an indeterminate neornithine.
References:
Mattia A. Baiano, Diego Pol, Flavio Bellardini, Guillermo J. Windholz, Ignacio A. Cerda, Alberto C. Garrido & Rodolfo A. Coria Elemgasem nubilus: a new brachyrostran abelisaurid (Theropoda, Ceratosauria) from the Portezuelo Formation (Upper Cretaceous) of Patagonia, Argentina (2022). https://doi.org/10.1002/spp2.1462
Letters from Gondwana. 