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Abelisauridae ("Abel's lizards") is a family (or clade) of ceratosaurian theropod dinosaurs. Abelisaurids thrived during the Cretaceous Period, on the ancient southern supercontinent of Gondwana and, today their fossil remains are found on the modern continents of Africa and South America, as well as on the Indian subcontinent and the island of Madagascar.
Like most theropods, abelisaurids were carnivorous bipeds. They were characterized by stocky hindlimbs and extensive ornamentation of the skull bones, with grooves and pits. In later abelisaurids, like Carnotaurus, the forelimbs became vestigial, the skull became shorter and bony crests developed above the eyes. Most of the known abelisaurids would have been between 5 to 9 meters (17 to 30 feet) in length, from snout to tip of tail.
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Anatomy
Complete skeletons have been described only for the most derived abelisaurids (Carnotaurus and Aucasaurus), making it difficult to establish synapomorphies (defining features) of the postcranial skeleton for the family as a whole. However, most are known from at least some skull material, so abelisaurid synapomorphies come mainly from the skull.
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Taxonomy and systematics
Paleontologists Jose Bonaparte and Fernando Novas coined the name Abelisauridae in 1985 when they described the eponymous Abelisaurus. The name is formed from the family name of Roberto Abel, who discovered Abelisaurus, as well as from the Greek word σαυρος/sauros meaning 'lizard'. The very common suffix -idae is usually applied to biological families and is derived from the Greek suffix -ιδαι/-idai, which indicates a plural noun.[Bonaparte, J.F. & Novas, F.E. 1985. Abelisaurus comahuensis, n.g., n.sp., Carnosauria of the Late Cretaceous of Patagonia. Ameghiniana. 21: 259-265. In Spanish]
Abelisauridae is a family in rank-based Linnaean taxonomy, within the infraorder Ceratosauria and the superfamily Abelisauroidea, which also contains the family Noasauridae. It has had several definitions in phylogenetic taxonomy. It was originally defined as a node-based taxon including Abelisaurus, Carnotaurus, their common ancestor and all of its descendants.[Novas, F.E. 1997. Abelisauridae. In: Currie, P.J. & Padian, K.P. Encyclopedia of Dinosaurs. San Diego: Academic Press. Pp. 1-2.][Sereno, P.C. 1998. A rationale for phylogenetic definitions, with applications to the higher-level taxonomy of Dinosauria. Neues Jahrbuch fur Geologie und Palaontologie: Abhandlungen 210: 41-83.] Later it was redefined as a stem-based taxon, including all animals more closely related to Abelisaurus (or the more complete Carnotaurus) than to Noasaurus.[ The node-based definition would not include animals like Rugops or Ilokelesia, which are thought to be more basal than Abelisaurus and would be included by a stem-based definition.][Sereno, P.C. 2005. Abelisauridae. TaxonSearch. 7 November 2005. Retrieved 19 September 2006.] Within Abelisauridae is the subgroup Carnotaurinae, and among carnotaurines, Aucasaurus and Carnotaurus are united in Carnotaurini.
Many abelisaurid skull features are shared with carcharodontosaurids. These shared features, along with the fact that abelisaurids seem to have replaced carcharodontosaurids in South America, have led to suggestions that the two groups were related.[ However, no cladistic analysis has ever found such a relationship and, aside from the skull, abelisaurids and carcharodontosaurids are very different, more similar to ceratosaurs and allosauroids, respectively.]
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Classification
Following is a list of abelisaurid genera by classification and location, assuming a stem-based definition:
FAMILY ABELISAURIDAE
Indosaurus may be a junior synonym of Indosuchus.
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Phylogeny
A 2004 phylogenetic analysis, performed by Paul Sereno of the University of Chicago and several colleagues, obtained the following results:[Sereno, P.C., Wilson, J.A., & Conrad, J.L. 2004. New dinosaurs link southern landmasses in the mid-Cretaceous. Proceedings of the Royal Society of London: Biological Sciences 271: 1325–1330.]
ABELISAUROIDEA
--NOASAURIDAE
ABELISAURIDAE
/--?Ilokelesia
--Abelisaurus
CARNOTAURINAE
--Rajasaurus
--Majungatholus
CARNOTAURINI
--Aucasaurus
Carnotaurus
Ilokelesia was originally described as a sister group to Abelisauroidea.[Coria, R.A. & Salgado, L. A basal Abelisauria Novas 1992 (Theropoda-]
Ceratosauria) from the Cretaceous Period of Patagonia, Argentina. In: Perez-Moreno, B, Holtz, T.R., Sanz, J.L., & Moratalla, J. (Eds.). Aspects of Theropod Paleobiology. Gaia 15:89–102. not printed until 2000 However, Sereno tentatively places it closer to Abelisaurus than to noasaurids, a result which agrees with several other recent analyses.[Calvo, J.O., Rubilar-Rogers, D., & Moreno, K. 2004. A new Abelisauridae (Dinosauria: Theropoda) from northwest Patagonia. Ameghiniana 41(4): 555-563.] If a stem-based definition is used, Ilokelesia and Rugops are therefore basal abelisaurids. However, as they are more basal than Abelisaurus, they are outside of Abelisauridae if the node-based definition is adopted. Ekrixinatosaurus was also published in 2004, so was not included in Sereno's analysis but an independent analysis, performed by Jorge Calvo and colleagues, shows it to be an abelisaurid.
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Evolution
Abelisauroids are typically regarded as a Cretaceous group, although possible abelisauroid remains are known from the Middle Jurassic of Madagascar.[Maganuco, S., Cau, A., & Pasini, G. 2005. First description of theropod remains from the Middle Jurassic (Bathonian) of Madagascar. Atti della Società Italiana di Scienze Naturali e del Museo Civico di Storia Naturale in Milano 146(2): 165-202.] Abelisaurid remains have only been found in the southern continents, which once made up the supercontinent of Gondwana. When first described in 1985, only Carnotaurus and Abelisaurus were known, both from the Late Cretaceous of South America. Abelisaurids were then located in Late Cretaceous India (Indosuchus and Rajasaurus) and Madagascar (Majungatholus), which were closely connected for much of the Cretaceous. It was thought that the absence of abelisaurids from continental Africa indicated that the group evolved after the separation of Africa from Gondwana, around 100 million years ago.[Sampson, S.D., Witmer, L.M., Forster, C.A., Krause, D.A., O'Connor, P.M., Dodson, P., Ravoavy, F. 1998. Predatory dinosaur remains from Madagascar: implications for the Cretaceous biogeography of Gondwana. Science 280: 1048-1051.] However, the discovery of Rugops and other abelisaurid material from the middle of the Cretaceous in northern Africa disproved this hypothesis.[Mahler, L. 2005. Record of Abelisauridae (Dinosauria: Theropoda) from the Cenomanian of Morocco. Journal of Vertebrate Paleontology 25(1): 236-239.] Mid-Cretaceous abelisaurids are now known from South America as well, showing that the group existed prior to the breakup of Gondwana.[Lamanna, M.C., Martinez, R.D., & Smith, J.B. 2002. A definitive abelisaurid theropod dinosaur from the early Late Cretaceous of Patagonia. Journal of Vertebrate Paleontology" 22(1): 58-69.]
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