Describer

Pol & Rauhut 2012

Time

Jurassic Middle Aalenian Bajocian

Classification

Saurischia Theropoda Abelisauridae

Diet

Carnivore

Fossilsite

Canadon Asfalto Formation, Jugo Loco locality, Cerro Condor, Chubut, Argentina

Info

Abelisaurids are a clade of large, bizarre predatory dinosaurs, most notable for their high, short skulls and extremely reduced forelimbs. They were common in Gondwana during the Cretaceous, but exceedingly rare in the Northern Hemisphere. The oldest definitive abelisaurids so far come from the late Early Cretaceous of South America and Africa, and the early evolutionary history of the clade is still poorly known. Here, we report a new abelisaurid from the Middle Jurassic of Patagonia, Eoabelisaurus mefi gen. et sp. nov., which predates the so far oldest known secure member of this lineage by more than 40 Myr. The almost complete skeleton reveals the earliest evolutionary stages of the distinctive features of abelisaurids, such as the modification of the forelimb, which started with a reduction of the distal elements. The find underlines the explosive radiation of theropod dinosaurs in the Middle Jurassic and indicates an unexpected diversity of ceratosaurs at that time. The apparent endemism of abelisauroids to southern Gondwana during Pangean times might be due to the presence of a large, central Gondwanan desert. This indicates that, apart from continent-scale geography, aspects such as regional geography and climate are important to reconstruct the biogeographical history of Mesozoic vertebrates.

Etymology

From eos, Greek for dawn, for the early occurrence of the new taxon, and Abelisaurus, type genus of the Abelisauridae. The species name refers to the popular
abbreviation of the Museo Paleontolo´gico Egidio Feruglio (MEF).

Holotype

Museo Paleontolo´gico Egidio Feruglio (MPEF) PV 3990, an almost complete skeleton, including the posterior half of the skull, five cervical and nine dorsal vertebrae, complete sacrum, 27 caudal vertebrae, left and right scapulocoracoid, left and right humerus, radius and ulna, left and right distal carpal, left and right metacarpals
I–IV, five phalanges (including one ungual) of the left and six phalanges (including one ungual) of the right hand,complete pelvic girdle, left and right femur, tibia,
fibula, tarsals and metatarsals, and 12 phalanges (including two uguals) of the left and eight phalanges (including one ungual) of the right pes

Type locality and horizon

Jugo Loco locality, close to the village of Cerro Condor, Chubut, Argentina. The locality is placed in a series of finely bedded mud-, marl- and limestones of the Canadon Asfalto Formation, early Middle Jurassic (Aalenian-Bajocian; see the electronic supplementary material).

Diagnosis

Medium-sized theropod dinosaur (6–6.5 m total length) with the following autapomorphies: quadrate with thickened medial distal articular end and subparallel
articular condyles; mid-dorsal vertebrae with double, V-shaped lamina extending from the parapophysis to the prezygodiapophyseal lamina; ulna with hypertrophied
olecranon process, accounting for more than 30 per cent of its length; pubic foramen elongate, more than twice as long as high; ambiens process of pubis developed
as a large, anterolaterally directed, convex expansion.

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