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| Joaquinraptor casali Ibiricu, Lamanna, Alvarez, Cerda, Caglianone, Cardozo, Luna & Martínez, 2025 Artwork by Andrew McAfee |
Abstract
Recent fossil discoveries have cast considerable light on the palaeobiology of Megaraptora, a group of large-clawed carnivorous theropod dinosaurs known from Cretaceous deposits in Asia, Australia, and especially South America. Nevertheless, many important aspects of megaraptoran morphology and evolution remain poorly understood, due in large part to the fragmentary nature of most fossils of these theropods and the scarcity of anatomically overlapping skeletal elements among the known taxa. Here we report a previously unknown megaraptoran genus and species represented by a partially articulated partial skeleton recovered from an uppermost Cretaceous stratum of the Lago Colhué Huapi Formation of south-central Chubut Province in central Patagonia, Argentina. Pertaining to the derived megaraptoran subclade Megaraptoridae, the taxon is among the most completely represented and latest-surviving megaraptorans. Its stratigraphic occurrence indicates that these dinosaurs likely persisted to the Cretaceous/Palaeogene boundary; moreover, the preservation of a crocodyliform humerus between the dentaries of the new theropod may provide information on megaraptoran dietary preferences and feeding strategies. Megaraptorids appear to have been the apex predators in central and southern Patagonian palaeoecosystems approaching the end of the Cretaceous, in contrast to more northerly areas of South America where these niches were occupied by other non-avian theropod groups.
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| Osteology of Joaquinraptor casali gen. et sp. nov. a Skeletal reconstruction of Joaquinraptor in left lateral view with preserved elements in blue (some reversed from right side) (modified and updated from Lamanna et al.7 [these authors’ Fig. 1e], which was in turn modified by A. McAfee from an original illustration by T.K. Robinson). Right maxilla in lateral (b) and medial (c) views. Skull roof, braincase, and atlantal intercentrum in dorsal (d) and ventral (e) views. f Probable right postorbital in lateral view. g Right quadrate in anterior view. Right and left dentaries in lateral and medial views (right dentary in lateral view and left dentary in medial view in h; opposite in i). j Two articulated middle or posterior caudal vertebrae in right lateral view. k Dorsal rib in anterior view. l Anterior haemal arch in anterior view. m Left scapulocoracoid in lateral view. Left humerus in anterolateral (n), lateral (o), and medial (p) views. Left radius in anterior (q) and lateral (r) views. Left ulna in lateral (s) and posterior (t) views. u Right manual ungual II (=manual phalanx II-3) in lateral view. Left femur in anterior (v) and posterior (w) views. x Distal right tibia in anterior view. y Right pedal ungual III (=pedal phalanx III-4) in medial view. Dashed lines indicate missing areas of scapulocoracoid and femur. |
Systematic palaeontology
Saurischia Seeley, 1887
Theropoda Marsh, 1881
Tetanurae Gauthier, 1986
Megaraptora Benson, Carrano, and Brusatte, 2010
Megaraptoridae Novas, Agnolín, Ezcurra, Porfiri, and Canale, 2013
Joaquinraptor casali gen. et sp. nov.
Etymology: Joaquín, in tribute to the son of the first author (L.M.I.) and the informal name given to the locality when the skeleton of the taxon was discovered (Valle Joaquín); Latin, raptor, thief. Specific epithet casali in recognition of Dr. Gabriel Andrés Casal for his many contributions to knowledge of the Cretaceous palaeontology and geology of central Patagonia (including the formal recognition and naming of the formation from which this megaraptorid was recovered).
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| Joaquinraptor casali with an ancient crocodile relative's front leg in its mouth. Artwork by Andrew McAfee |
Lucio M. Ibiricu, Matthew C. Lamanna, Bruno N. Alvarez, Ignacio A. Cerda, Julieta L. Caglianone, Noelia V. Cardozo, Marcelo Luna and Rubén D. Martínez. 2025. Latest Cretaceous megaraptorid theropod Dinosaur sheds light on megaraptoran evolution and palaeobiology. Nature Communications. 16: 8298. DOI: doi.org/10.1038/s41467-025-63793-5 [23 September 2025]
