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| Maip macrothorax Aranciaga Rolando, Motta, Agnolín, Manabe, Tsuihiji & Novas, 2022 |
Abstract
Megaraptora is a theropod clade known from former Gondwana landmasses and Asia. Most members of the clade are known from the Early to Late Cretaceous (Barremian–Santonian), with Maastrichtian megaraptorans known only from isolated and poorly informative remains. The aim of the present contribution is to describe a partial skeleton of a megaraptorid from Maastrichtian beds in Santa Cruz Province, Argentina. This new specimen is the most informative megaraptoran known from Maastrichtian age, and is herein described as a new taxon. Phylogenetic analysis nested the new taxon together with other South American megaraptorans in a monophyletic clade, whereas Australian and Asian members constitute successive stem groups. South American forms differ from more basal megaraptorans in several anatomical features and in being much larger and more robustly built.
SYSTEMATIC PALAEONTOLOGY
Theropoda Marsh, 1881
Tetanurae Gauthier, 1986
Coelurosauria von Huene, 1920
Megaraptora Benson et al., 2010
Megaraptoridae Novas et al., 2013
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| (A), silhouette of Maip macrothorax showing the preserved bones in white. (B), reconstruction of the thoracic cavity of Maip at level of D6. (C), interpretative drawing of the excavation of Maip showing the original disposition of the bones. Abbreviations: a, axis; c, coracoid; ind, indeterminate bone; g, gastralia; r, rib; v, vertebrae. |
Maip macrothorax gen. et sp. nov.
Derivation of name. Maip is an evil entity from the Aonikenk mythology that represents “the shadow of the death” which “kills with cold wind”, and roams in the Andes mountains. The specific name, macro, derives from the Latin “big” and “thorax” refers to its wide thoracic cavity (which has, approximately, more than 1.20 m width).
Locality. Megaraptorid Site (Locality 3; see Novas et al.3), La Anita Farm, 30 km West from El Calafate city, Santa Cruz province, Argentina. Chorrillo Formation (Maastrichtian;3,37,38).
Diagnosis. Megaraptorid theropod diagnosable on the basis of the following combination of characters (autapomorphies marked by an asterisk): 1) mid-dorsal vertebrae with articular surface of parapophyses saddle-shaped (absent in Aerosteon and Murusraptor)*; 2) mid-caudal vertebrae with an accessory posterior centrodiapophyseal lamina that subdivides the postzygapophyseal-centrodiapophyseal fossa in two pneumatic fossae (absent in Aoniraptor, Aerosteon, Megaraptor, and Orkoraptor)*; 3) first dorsal rib with honey-comb internal structure on its tubercle (absent in Australovenator, Megaraptor, and Murusraptor); 4) prominent anterior projection on the coracoid (absent in Fukuiraptor, Aerosteon, and Megaraptor)*; 5) coracoid without a subglenoid ridge (subglenoid ridge present in Aerosteon)*; 6) coracoid without a posteroventral fossa (posteroventral fossa present in Fukuiraptor, Aerosteon, and Megaraptor); and 7) and coracoid with ventromedial margin forming a dorsoventrally deep articular surface for the sternum (absent in Fukuiraptor, Aerosteon, and Megaraptor)*.
Alexis M. Aranciaga Rolando, Matias J. Motta, Federico L. Agnolín, Makoto Manabe, Takanobu Tsuihiji and Fernando E. Novas. 2022. A large Megaraptoridae (Theropoda: Coelurosauria) from Upper Cretaceous (Maastrichtian) of Patagonia, Argentina. Scientific Reports. 12, 6318. DOI: 10.1038/s41598-022-09272-z
Alexis M. Aranciaga Rolando, Matias J. Motta, Federico L. Agnolín, Makoto Manabe, Takanobu Tsuihiji and Fernando E. Novas. 20xx. The Biggest Megaraptoridae (Theropoda: Coelurosauria) of South America. DOI: 10.21203/rs.3.rs-1152394/v1
Abstract: Megaraptorans are a theropod clade distributed in former Gondwana landmasses and Asia. Most members of the clade are known from early Cretaceous to Turonian times whereas Maastrichtian megaraptorans are known just from isolated and poorly informative remains. The aim of present contribution is to describe a partial skeleton of a megaraptorid coming from Maastrichtian beds at Santa Cruz province, Argentina. This new taxon constitutes the most informative megaraptoran from post-Turonian beds. Phylogenetic analysis nested the new taxon together with South American megaraptorans in a monophyletic clade, whereas Australian and Asian members constitute successive stem groups. South American forms differ from more basal megaraptorans in several anatomical features and in being much larger and more robustly built. It is possible that the Cenomanian-Turonian extinction of carcharodontosaurids was allowed to megaraptorans to occupy the niche of top predators in South America.
KEYWORDS: Megaraptoridae, Maastrichtian, South America, Patagonia
