Abstract
We describe the new basal abelisauroid dinosaur Austrocheirus isasii gen. et sp. nov. from the Late Cretaceous Pari Aike Formation of southwestern Patagonia, Argentina. The preserved remains include manual bones, a distal tibia, and some pedal and axial elements. Austrocheirus is differentiated from other basal theropods by the presence of metacarpal III with a dorsoventrally compressed shaft and posteriorly displaced collateral tendon fossae located at the same level of the proximal end of distal condyles, and pedal phalanges with a conspicuous longitudinal crest delimitating the dorsal margin of the distal collateral tendon fossae. A cladistic analysis recovered the new species as more derived than Ceratosaurus and Berberosaurus, but within a polytomy at the base of Abelisauroidea, an assignment supported by two abelisauroid synapomorphies: distal end of tibia with a planar vertical scar for the reception of the ascending process of the astragalus that occupies most of its anterior surface and is medially bounded by the longitudinally oriented facet; and scar for the reception of the ascending process with a median vertical ridge, which imbeds into a crescentic vertical groove on the posterior surface of the ascending process of the astragalus forming an interlocking tibiotarsal articulation. Furthermore, Austrocheirus represents the first known medium-sized Late Cretaceous abelisauroid bearing nonatrophied hands. The evidence provided here suggests that the strong reduction of the forelimb recorded in derived abelisaurids is not directly correlated with their increased body-size, but it seems to be an evolutionary event exclusive to this lineage within Ceratosauria.References
Agnolin, F.L. & Chiarelli, P. (in press) The position of the claws in Noasauridae (Dinosauria: Abelisauroidea) and its implications for abelisauroid manus evolution. Paläontologische Zeitschrift (DOI: 10.1007/s12542-009-0044-2).
Agnolin, F.L., Ezcurra, M.D. & Pais, D.F. (2005) Systematic reinterpretation of the pigmy Allosaurus from the Lower Cretaceous of Victoria (Australia). Ameghiniana, 42, 13R.
Allain, R., Tykoski, R., Aquesbi, N., Jalil, N.-E., Monbaron, M., Russell, D. & Taquet, P. (2007) An abelisauroid (Dinosauria: Theropoda) from the Early Jurassic of the High Atlas Mountains, and the radiation of ceratosaurs. Journal of Vertebrate Paleontology, 27, 610–624.
Ambrosio, A. (2003) Estratigrafía, sedimentología y pelontología de las adyacencias del valle del río La Leona, Cretácico y Terciario, provincia de Santa Cruz. Trabajo Final de Tesis de Licenciatura, Universidad de Buenos Aires, Buenos Aires, 130 pp.
Benson, R.B.J. (in press) A description of Megalosaurus bucklandii (Dinosauria: Theropoda) from the Bathonian of the UK and the relationships of Middle Jurassic theropods. Zoological Journal of the Linnean Society (DOI: 10.1111/j.1096-3642.2009.00569.x.).
Benson, R.B.J., Carrano, M.T. & Brusatte, S.L. (2010) A new clade of archaic large-bodied predatory dinosaurs (Theropoda: Allosauroidea) that survived to the latest Mesozoic. Naturwissenschaften, 97, 71–78.
Bonaparte, J.F. (1985) A horned Cretaceous carnosaur from Patagonia. National Geographic Research, 1, 150–152.
Bonaparte, J.F. (1991) Los vertebrados fósiles de la Formación Río Colorado, de la ciudad de Nequén y cercanias, Cretácico Superior, Argentina. Revista del Museo Argentino de Ciencias Naturales ‘‘Bernardino Rivadavia’’, Paleontología, 4, 17–123.
Bonaparte, J.F. (1996) Cretaceous tetrapods of Argentina. Münchner Geowissenschaften Abhandlungen, 30, 73–130
Bonaparte, J.F. & Powell, J. (1980) A continental assemblage of tetrapods from the Upper Cretaceous beds of El Brete, northwestern Argentina (Sauropoda-Coelurosauria-Carnosauria-Aves). Mémoires de la Societé Géologique de la France, Nouvelle Série, 139, 19–28.
Bonaparte, J.F. & Novas, F.E. (1985) Abelisaurus comahuensis, n. g. n. sp., Carnosauria del Cretácico Tardío de Patagonia. Ameghiniana, 21, 259–265.
Bonaparte, J.F., Novas, F.E. & Coria, R. A. (1990) Carnotaurus sastrei Bonaparte, the horned, lightly built carnosaur from the Middle Cretaceous of Patagonia. Contributions in Science, Natural History Museum of Los Angeles County, 416, 1–41.
Britt, B.B. (1991) Theropods of Dry Mesa Quarry (Morrison Formation, Late Jurassic), Colorado, with emphasis on the osteology of Torvosaurus tanneri. Brigham Young Geological Studies, 37, 1–72.
Brochu, C.A. (2003) Osteology of Tyrannosaurus rex: insights from a nearly complete skeleton and high resolution computed tomographic analysis of the skull. Memoirs of the Society of Vertebrate Paleontology, 7, 1–138.
Brusatte, S.L., Benson, R.B.J & Hutt, S. (2008) The osteology of Neovenator salerii (Dinosauria: Theropoda) from the Walden Group (Barremian) of the Isle of Wight. Monograph of the Palaeontographical Society, 162, 1–75.
Burch, S. & Carrano, M.C. (2008) Abelisaurid forelimb evolution: new evidence from Majungasaurus crenatissimus (Abelisauridae: Theropoda) from the Late Cretaceous of Madagascar. Journal of Vertebrate Paleontology, 28 (suppl. to 3), 58A.
Burke, A.C. & Feduccia, A. (1997) Developmental patterns and the identification of homologies in the avian hand. Science, 278, 666–669.
Calvo, J.O., Porfiri, J.D., Veralli, C., Novas, F.E. & Poblete, F. (2004) Phylogenetic status of Megaraptor namunhuaiquii Novas based on a new specimen from Neuquén, Patagonia, Argentina. Ameghiniana, 41, 565–575.
Canale, J.I., Scanferla, C.A., Agnolin, F.L. & Novas, F.E. (2009) New carnivorous dinosaur from the Late Cretaceous of NW Patagonia and the evolution of abelisaurid theropods. Naturwissenschaften, 96, 409–414.
Carrano, M.T. (2007) The appendicular skeleton of Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. Memoirs of the Society of Vertebrate Paleontology, 8, 163–179.
Carrano, M.T. & Hutchinson, J.R. (2002) Pelvic and hindlimb musculature of Tyrannosaurus rex (Dinosauria: Theropoda). Journal of Morphology 253, 207–228.
Carrano, M.T. & Sampson, S.D. (2008) The phylogeny of Ceratosauria (Dinosauria: Theropoda). Journal of Systematic Palaeontology, 6, 182–236.
Carrano, M.T., Sampson, S.D. & Forster, C.A. (2002) The osteology of Masiakasaurus knopfleri, a small abelisauroid (Dinosauria: Theropoda) from the Late Cretaceous of Madagascar. Journal of Vertebrate Paleontology, 22, 510–534.
Chinsamy-Turan, A. (2005) The Microstructure of Dinosaur Bone. Johns Hopkins University Press, Baltimore, 216 pp.
Coddington, J.A. & Scharff, N. (1994) Problems with zero-length branches. Cladistics, 10, 415–423.
Coria, R.A. & Salgado, L. (1995). A new giant carnivorous dinosaur from the Cretaceous of Patagonia. Nature, 377, 224–226.
Coria, R.A. & Salgado, L. (2000) A basal Abelisauria Novas 1992 (Theropoda-Ceratosauria) from the Cretaceous of Patagonia, Argentina. Gaia, 15, 89–102.
Coria, R.A. & Currie, P.J. (2006) A new carcharodontosaurid (Dinosauria, Theropoda) from the Upper Cretaceous of Argentina. Geodiversitas, 28, 71–118.
Coria, R.A., Chiappe, L.M. & Dingus, L. (2002) A new close relative of Carnotaurus sastrei Bonaparte 1985 (Theropoda: Abelisauridae) from the Late Cretaceous of Patagonia. Journal of Vertebrate Paleontology, 22, 460–465.
Cormack, D.H. (1987) Ham’s histology. 9th Edition. J.B. Lippincott Company, Philadelphia, 183 pp.
Currie, P.J. & Zhao X.J. (1993) A new carnosaur (Dinosauria, Theropoda) from the Jurassic of Xinjiang, People´s Republic of China. Canadian Journal of Earth Sciences, 30, 2037–2247.
Currie, P.J. & Carpenter, K. (2000) A new specimen of Acrocanthosaurus atokensis (Dinosauria: Theropoda) from the Lower Cretaceous Antler Formation (Lower Cretaceous, Aptian) of Oklahoma, USA. Geodiversitas, 22, 207–246.
Erickson, G.M. (2005) Assessing dinosaur growth patterns: a microscopic revolution. Trends in Ecology and Evolution, 20, 677–684.
Ezcurra, M.D. & Novas, F.E. (2007) Phylogenetic relationships of the Triassic theropod Zupaysaurus rougieri from NW Argentina. Historical Biology, 19, 35–72.
Galton, P.M. & Jensen, J.A. (1979) A new large theropod dinosaur from the Upper Jurassic of Colorado. Brigham Young University of Geological Studies, 26, 1–12.
Gao, Y. (1993) A new species of Middle Jurassic Carnosauria from Dashanpu, Zigong, Sichaun Province, Szechuanosaurus zigongensis sp. nov. Vertebrata PalAsiatica, 31, 308–314.
Gauthier, J. (1986) Saurischian monophyly and the origin of birds. In: Padian, K. (Ed.). The Origin of Birds and the Evolution of Flight. Memoirs of the California Academy of Sciences, 8, 1–55.
Gilmore, C.W. (1920) Osteology of the carnivorous Dinosauria in the United States National Museum, with special reference to the genera Antrodemus (Allosaurus) and Ceratosaurus. Bulletin of the United States National Museum, 110, 1–154.
Goloboff, P.A., Farris, J.S. & Nixon, K. (2008) TNT, a free program for phylogenetic analysis. Cladistics, 24, 774–786.
Hayashi, S., Carpenter, K. & Suzuki, D. (2009) Different growth patterns between the skeleton and osteoderms of Stegosaurus (Ornithischia: Thyreophora). Journal of Vertebrate Paleontology, 29, 123–131.
Holtz, T.R. (2000) A new phylogeny of carnivorous dinosaurs. Gaia, 15, 5-61.
Janensch, W. (1925) Die Coelurosaurier und Theropoden der Tendaguru-schichten Deutsch-Ostafrikas. Palaeontologica, 1, 1–99.
Kellner, A.W.A. & Campos, D.A. (2002) On a theropod dinosaur (Abelisauria) from the continental Cretaceous of Brazil: Arquivos do Museu Nacional de Rio Janeiro, 60, 163–170.
Klein, N. & Sander, M. (2008) Ontogenetic stages in the long bone histology of sauropod dinosaurs. Paleobiology, 34, 247–263.
Kraemer, P. & Riccardi, A. (1997) Estratigrafía de la región comprendida entre los lagos Argentino y Viedma (49° 400’-50° 10’ lst. S), Provincia de Santa Cruz. Revista de la Asociación Geológica Argentina, 52, 333–360.
Lamanna, M.C., Martinez, R.D. & Smith, J.B. (2001) A definitive abelisaurid theropod dinosaur from the early Late Cretaceous of Patagonia. Journal of Vertebrate Paleontology, 22, 58–69.
Long, J.A. & Molnar, R.E. (1998) A new Jurassic theropod dinosaur from Western Australia. Records of the Western Australian Museum, 19, 221–229.
Madsen Jr., J. H. (1976) Allosaurus fragilis: a revised osteology. Utah Geological and Mineral Survey Bulletin, 109, 1–163.
Madsen Jr., J. H. & Welles, S. P. (2000) Ceratosaurus (Dinosauria, Theropoda) a revised osteology. Miscellaneous Publication Utah Geological Survey, 1–80.
Makovicky, P.J., Apesteguía, S. & Agnolin, F.L. (2005) The earliest dromaeosaurid theropod from South America. Nature, 437, 1007–1011.
Marsh, O.C. (1881) Principal characters of American Jurassic dinosaurs. Part V. American Journal of Science, series 3, 21, 417–423.
Marsh, O.C. (1884) Principal characters of American Jurassic dinosaurs. Part VIII. The order Theropoda. American Journal of Science, 27, 329–340.
Martill, M.D., Cruickshank, A.R.I., Frey, E., Small, P.G. & Clarke, M. (1996) A new crested maniraptoran dinosaur from the Santana Formation (Lower Cretaceous) of Brazil. Journal of the Geological Society, London, 153, 5–8.
Martinelli, A.G. & Vera, E.I. (2007) Achillesaurus manazzonei, a new alvarezsaurid theropod (Dinosauria) from the Late Cretaceous Bajo de la Carpa Formation, Rio Negro Province, Argentina. Zootaxa, 1582, 1–17.
Martinez, R., Gimenez, O., Rodríguez, J. & Bochatey, G. (1986) Xenotarsosaurus bonapartei gen. et. sp. nov. (Carnosauria, Abelisauridae), un nuevo Theropoda de la Formación Bajo Barreal, Chubut, Argentina. Actas IV Congreso Argentino de Paleontología y Bioestratigrafía, 2, 23–31.
Naish, D., Martill, D.M. & Frey, E. (2004) Ecology, systematics and biogeographical relationships of dinosaurs, including a new theropod, from the Santana Formation (?Albian, Early Cretaceous) of Brazil. Historical Biology, 2004, 1–14.
Novas, F.E. (1992) La evolución de los dinosaurios carnívoros. In: Sanz, J.L. & Buscalioni, A.D. (Eds.). Los dinosaurios y su entorno biótico. Actas del segundo curso de paleontología en Cuenca. Instituto “Juan de Valdez”, Cuenca, España, pp 125–163.
Novas, F.E. (1996) Dinosaur monophyly. Journal of Vertebrate Paleontology, 16, 723–741.
Novas, F.E. (1997a) Anatomy of Patagonykus puertai (Theropoda, Avialae, Alvarezsauridae), from the Late Cretaceous of Patagonia. Journal of Vertebrate Paleontology, 17, 137–166.
Novas, F.E. (1997b) Abelisauridae. In: Currie, P.J. & Padian, K. (Eds.). Encyclopedia of Dinosaurs. Academic Press, San Diego, pp 1–2.
Novas, F.E. & Puerta, P.F. (1997) New evidence concerning avian origins from the Late Cretaceous of Patagonia. Nature, 387, 390–392.
Novas, F.E. & Bandyopadhyay, S. (2001) Abelisaurid pedal unguals from the Late Cretaceous of India. In: VII International Symposium on Mesozoic Terrestrial Ecosystems. Asociacion Paleontologica Argentina, Publicacion Especial, 7, 145–149.
Novas, F.E. & Pol, D. (2005) New evidence on deinonychosaurian dinosaurs from the Late Cretaceous of Patagonia. Nature, 433, 858–861.
Novas, F.E., Cambiaso, A.V. & Ambrosio, A. (2004) A new basal iguanodontian (Dinosauria, Ornithischia) from the Upper Cretaceous of Patagonia. Ameghiniana, 41, 75–82.
Novas, F.E., de Valais, S., Vickers-Rich, P. & Rich, T. (2005a) A large Cretaceous theropod from Patagonia, Argentina, and the evolution of carchadorontosaurids. Natturwissenschaften, 92, 226–230.
Novas, F.E., Salgado, L., Calvo, J.O. & Agnolín, F.L. (2005b) Giant titanosaur (Dinosauria, Sauropoda) from the Late Cretaceous of Patagonia. Revista del Museo Argentino de Ciencias Naturales, nueva serie, 7, 37–41.
Novas, F.E., Ezcurra, M.D. & Lecuona, A. (2008) Orkoraptor burkei nov. gen. et sp., a large theropod from the Maastrichtian Pari Aike Formation, Southern Patagonia, Argentina. Cretaceous Research, 29, 468–480.
Novas, F.E., Pol, D., Canale, J.I., Porfiri J.D. & Calvo, J.O. (2009) A bizarre Cretaceous theropod dinosaur from Patagonia and the evolution of Gondwanan dromaeosaurids. Proceedings of the Royal Society B, 276, 1101–1107.
O'Connor, P.M. (2007) The postcranial axial skeleton of Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. Memoirs of the Society of Vertebrate Paleontology, 8, 127–162.
Ostrom, J.H. (1969) Osteology of Deinonychus antirrhopus, an unusual theropod from the Lower Cretaceous of Montana. Bulletin of the Peabody Museum of Natural History, 30, 1–165.
Paul, G.S. (2002) Dinosaurs of the Air. The Johns Hopkins University Press, Baltimore and London, 460 pp.
Raath, M.A. (1990) Morphological variation in small theropods and its meaning in systematics: evidence from Syntarsus rhodesiensis. In: Carpenter, K. & Currie, P.J. (Eds.). Dinosaur Systematics: Perspectives and Approaches. Cambridge University Press, Cambridge, pp 91–105.
Ramirez, M.A. & von Baczko, M.B. (2009) Material de Theropoda (Dinosauria) de la Formación Pari Aike (Cretácico Superior), Santa Cruz, Argentina. Ameghiniana: in press.
Rauhut, O.W.M. (2003) The interrelationships and evolution of basal theropod dinosaurs. Special Papers in Paleontology, 69, 1–214.
Rauhut, O.W.M. (2004) Provenance and anatomy of Genyodectes serus, a large-toothed ceratosaur (Dinosauria: Theropoda) from Patagonia. Journal of Vertebrate Paleontology, 24, 894–902.
Rauhut, O.W.M. (2005) Postcranial remains of ‘‘coelurosaurs’’ (Dinosauria, Theropoda) from the Late Jurassic of Tanzania. Geological Magazine, 142, 97–107.
Rauhut, O.W.M., Cladera, G., Vickers-Rich, P. & Rich, T.H. (2003) Dinosaur remains from the Lower Cretaceous of the Chubut Group, Argentina. Cretaceous Research, 24, 487–497.
Rowe, T. & Gauthier, J. A. (1990) Ceratosauria. In: Weishampel, D.B., Dodson, P. & Osmólska, H. (Eds.), The Dinosauria, 1st Edition. University of California Press, Berkeley and Los Angeles, pp. 151–168.
Russell, D.A. & Dong, Z.M. (1993) A nearly complete skeleton of a new troodontid dinosaur from the Early Cretaceous of the Ordos Basin, Inner Mongolia, People's Republic of China. Canadian Journal of Earth Sciences, 30, 2163–2173.
Sampson, S., Witmer, L., Forster, C., Krause, D., O'Connor, P., Dodson, P. & Rovoavy, F. (1998) Predatory dinosaur remains from Madagascar: implications for the Cretaceous biogeography of Gondwana. Science, 280, 1048–1051.
Sampson, S.D., Carrano, M.T. & Forster, C.A. (2001) A bizarre predatory dinosaur from the Late Cretaceous of Madagascar. Nature, 409, 504–509.
Sander, P.M. (2000) Longbone histology of the Tendaguru sauropods: implications for growth and biology. Paleobiology, 26, 466–488.
Sereno, P.C. (1993) The pectoral girdle and forelimb of the basal theropod Herrerasaurus ischigualastensis. Journal of Vertebrate Paleontology, 13, 425–450.
Sereno, P.C. (1999) The evolution of dinosaurs. Science 284: 2137–2147.
Sereno, P.C. & Brusatte, S.L. (2008) Basal abelisaurid and carcharodontosaurid theropods from the Lower Cretaceous Elrhaz Formation of Niger. Acta Palaeontologica Polonica, 53, 15–46.
Sereno, P.C., Wilson, J.A. & Conrad, J.L. (2004) New dinosaurs link landmasses in the Mid-Cretaceous. Proceedings of the Royal Society of London B, 271, 1325–1330.
Smith, J.B. (2007) Dental morphology and variation in Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretceous of Madagascar. Memoirs of the Society of Vertebrate Paleontology, 8, 103–126.
Tykoski, R.S. & Rowe, T. (2004) Ceratosauria. In: Weishampel, D.B., Dodson, P. & Osmólska, H. (Eds.). The Dinosauria, 2nd Edition. University of California Press, Berkeley and Los Angeles, pp. 151–168.
Tykoski, R.S. (2005) Anatomy, Ontogeny, and Phylogeny of Coelophysoid theropods. Unpublished Ph.D. dissertation, University of Texas at Austin, 572 pp.
Wagner, G. & Gauthier, J. (1999) 1,2,3 = 2,3,4: a solution to the problem of the homology of digits in the avian hand. Proceedings of the National Academy of Sciences, 96, 5111–5116.
Welles, S.P. (1984) Dilophosaurus wetherilli (Dinosauria, Theropoda): osteology and comparisons. Palaeontographica Abteilung A, 185, 85–180.
Welles, S.P. & Long, R.A. (1974) The tarsus of theropod dinosaurs. Annals of the South African Museum, 64, 191–218.
Wilson, J.A., Sereno, P.C., Srivastava, S., Bhatt, D.K., Khosla, A. & Sahni, A. (2003) A new abelisaurid (Dinosauria, Theropoda) from the Lameta Formation (Cretaceous, Maastrichtian) of India. Contributions from the Museum of Paleontology, the University of Michigan, 31, 1–42.
Xu, X., Tan, Q., Wang, J., Zhao, X. & Tan, L. 2007. A gigantic bird-like dinosaur from the Late Cretaceous of China. Nature, 447, 884–847.
Xu, X., Clark, J.M., Mo J., Choiniere, J., Forster, C.A., Erickson, G.M., Hone, D.W.E., Sullivan, C., Eberth, D.A., Nesbitt, S., Zhao, Q., Hernandez, R., Jia, C., Han, F. & Guo, Y. (2009) A Jurassic ceratosaur from China helps clarify avian digital homologies. Nature, 459, 940–944.