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==Anatomy==
==Anatomy==
Complete skeletons have been described only for the most [[derived]] abelisaurids (''Carnotaurus'' and ''[[Aucasaurus]]''), making it difficult to establish [[synapomorphy|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.<ref name="tykoskirowe2004">Tykoski, R.S. & Rowe, T. (2004). "Ceratosauria". In: Weishampel, D.B., Dodson, P., & Osmolska, H. (Eds.) ''The Dinosauria'' (2nd edition). Berkeley: University of California Press. Pp. 47–70.</ref>
Complete skeletons have been described only for the most [[derived]] abelisaurids (''Carnotaurus'' and ''[[Aucasaurus]]''), making it difficult to establish [[synapomorphy|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.<ref name="tykoskirowe2004">Tykoski, R.S. & Rowe, T. (2004). "Ceratosauria". In: Weishampel, D.B., Dodson, P., & Osmolska, H. (Eds.) ''The Dinosauria'' (2nd edition). Berkeley: University of California Press. Pp. 47–70 ISBN 0-520-24209-2</ref>
[[Image:Abelisaurus comahuensis.JPG|thumb|left|250px|Reconstructed ''[[Abelisaurus]]'' skull featured in the traveling "[[Dinosaur]]s of [[Patagonia]]" exhibit. Note the rough bone surfaces and projections from the lacrimal and postorbital bones into the eye socket.]]
[[Image:Abelisaurus comahuensis.JPG|thumb|left|250px|Reconstructed ''[[Abelisaurus]]'' skull featured in the traveling "[[Dinosaur]]s of [[Patagonia]]" exhibit. Note the rough bone surfaces and projections from the lacrimal and postorbital bones into the eye socket.]]
Although skull proportions varied, abelisaurid skulls were generally very tall and often very short. In ''Carnotaurus'', for example, the skull was nearly as tall as it was long. The [[premaxilla]] in abelisaurids was very tall, so the front of the snout was blunt, not tapered as seen in many other theropods. The [[lacrimal bone|lacrimal]] and [[postorbital]] bones projected into the [[Orbit (anatomy)|orbit]] (eye socket) from the front and back, nearly dividing it into two compartments. The eye would have been located in the upper compartment of the orbit, which was tilted slightly outwards in ''Carnotaurus'', perhaps providing some degree of [[binocular vision]]. The lacrimal and postorbital also met above the orbit, to form a pronounced ridge or brow above the eye. Extensive sculpturing is seen on many of the skull bones, in the form of long grooves, pits and protrusions. Like other ceratosaurs, the [[frontal bone]]s of the skull roof were fused together. Carnotaurine abelisaurids commonly had bony projections from the frontals. ''Carnotaurus'' had two pronounced horns on the frontals, projecting laterally above the eyes, while its close relative ''Aucasaurus'' had smaller projections in the same area. ''[[Majungasaurus]]'' and ''[[Rajasaurus]]'' had a single bony horn or dome, projecting upwards from the fused frontals. These projections, like the horns of many modern animals, might have been [[display (zoology)|display]]ed for species recognition or intimidation.<ref name="tykoskirowe2004"/><ref name="bonaparteetal1990">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 to Science of the Natural History Museum of Los Angeles County'' 416: 1–42.</ref><ref name="wilsonetal2003">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 of the Museum of Palaeontology of the University of Michigan'' 31: 1–42.</ref>
Although skull proportions varied, abelisaurid skulls were generally very tall and often very short. In ''Carnotaurus'', for example, the skull was nearly as tall as it was long. The [[premaxilla]] in abelisaurids was very tall, so the front of the snout was blunt, not tapered as seen in many other theropods. The [[lacrimal bone|lacrimal]] and [[postorbital]] bones projected into the [[Orbit (anatomy)|eye socket]] from the front and back, nearly dividing it into two compartments. The eye would have been located in the upper compartment of the orbit, which was tilted slightly outwards in ''Carnotaurus'', perhaps providing some degree of [[binocular vision]]. The lacrimal and postorbital also met above the orbit, to form a pronounced ridge or brow above the eye. Extensive sculpturing is seen on many of the skull bones, in the form of long grooves, pits and protrusions. Like other ceratosaurs, the [[frontal bone]]s of the skull roof were fused together. Carnotaurine abelisaurids commonly had bony projections from the frontals. ''Carnotaurus'' had two pronounced horns on the frontals, projecting laterally above the eyes, while its close relative ''Aucasaurus'' had smaller projections in the same area. ''[[Majungasaurus]]'' and ''[[Rajasaurus]]'' had a single bony horn or dome, projecting upwards from the fused frontals. These projections, like the horns of many modern animals, might have been [[display (zoology)|display]]ed for species recognition or intimidation.<ref name="tykoskirowe2004"/><ref name="bonaparteetal1990">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 to Science of the Natural History Museum of Los Angeles County'' 416: 1–42.</ref><ref name="wilsonetal2003">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 of the Museum of Palaeontology of the University of Michigan'' 31: 1–42.</ref>


The forelimbs are known only in the carnotaurine abelisaurids, ''Aucasaurus'' and ''Carnotaurus'', in which they were vestigial. The [[Radius (bone)|radius]] and [[ulna]] were extremely short, only 25% of the length of the [[humerus]] in ''Carnotaurus'' and 33% in ''Aucasaurus''. Typically for ceratosaurs, the carnotaurine [[Manus (zoology)|manus]] ('hand') contained four digits. However, it is there that any similarity ends. No [[carpal]] (wrist) bones existed, with the four [[metacarpal]]s articulating directly with the radius and ulna. There were no [[phalanges]] on the first or fourth digits, one on the second digit and two on the third digit. The forelimbs do not appear to have borne claws. It is unknown if this peculiar forelimb [[morphology (biology)|morphology]] applies to other abelisaurids, as their forelimbs have not been discovered.<ref name="coriaetal2002">Coria, R.A., Chiappe, L.M. & Dingus, L. (2002). "A close relative
The forelimbs are known only in the carnotaurine abelisaurids, ''Aucasaurus'' and ''Carnotaurus'', in which they were vestigial. The [[Radius (bone)|radius]] and [[ulna]] were extremely short, only 25% of the length of the [[humerus]] in ''Carnotaurus'' and 33% in ''Aucasaurus''. Typically for ceratosaurs, the carnotaurine [[Manus (zoology)|hand]] contained four digits. However, it is there that any similarity ends. No [[carpal|wrist]] bones existed, with the four [[metacarpal]]s articulating directly with the radius and ulna. There were no [[phalanges]] on the first or fourth digits, one on the second digit and two on the third digit. The forelimbs do not appear to have borne claws. It is unknown if this peculiar forelimb [[morphology (biology)|morphology]] applies to other abelisaurids, as their forelimbs have not been discovered.<ref name="coriaetal2002">Coria, R.A., Chiappe, L.M. & Dingus, L. (2002). "A close relative
of ''Carnotaurus sastrei'' Bonaparte 1985 (Theropoda: Abelisauridae) from the Late Cretaceous of Patagonia". ''Journal of Vertebrate Palaeontology'' 22: 460–465.</ref> Abelisaurid hindlimbs were more typical of ceratosaurs, with the [[astragalus]] and [[calcaneum]] (upper ankle bones) fused to each other and to the [[tibia]], forming a tibiotarsus. The tibia was shorter than the [[femur]], giving the hindlimb stocky proportions. There were three functional digits on the foot (the second, third, and fourth), while the first digit, or [[hallux]], did not contact the ground.<ref name="tykoskirowe2004"/>
of ''Carnotaurus sastrei'' Bonaparte 1985 (Theropoda: Abelisauridae) from the Late Cretaceous of Patagonia". ''Journal of Vertebrate Palaeontology'' 22: 460–465.</ref> Abelisaurid hindlimbs were more typical of ceratosaurs, with the [[astragalus]] and [[calcaneum|upper ankle bones]] fused to each other and to the [[tibia]], forming a tibiotarsus. The tibia was shorter than the [[femur]], giving the hindlimb stocky proportions. There were three functional digits on the foot (the second, third, and fourth), while the first digit, or [[hallux]], did not contact the ground.<ref name="tykoskirowe2004"/>


==Taxonomy and systematics==
==Taxonomy and systematics==
[[Paleontologist]]s [[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 [[Ancient Greek|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.<ref name="bonapartenovas1985">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]</ref>
[[Paleontologist]]s [[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 [[Ancient Greek|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.<ref name="bonapartenovas1985">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]</ref>
[[Image:Carnotaurus DB.jpg|thumb|right|300px|''Carnotaurus sastrei'' life restoration.]]
[[Image:Carnotaurus DB.jpg|thumb|right|300px|''Carnotaurus sastrei'' life restoration.]]
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.<ref name="novas1997">Novas, F.E. (1997). "Abelisauridae". In: Currie, P.J. & Padian, K.P. ''Encyclopedia of Dinosaurs''. San Diego: Academic Press. Pp. 1–2.</ref><ref name="sereno1998">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.</ref> 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''.<ref name="wilsonetal2003"/> The node-based definition would not include animals like ''[[Rugops]]'' or ''[[Ilokelesia]]'', which are thought to be more [[Basal (phylogenetics)|basal]] than ''Abelisaurus'' and would be included by a stem-based definition.<ref name="taxonsearch">Sereno, P.C. (2005). [http://www.taxonsearch.org/dev/taxon_edit.php?Action=View&tax_id=6 Abelisauridae]. TaxonSearch. 7 November 2005. Retrieved 19 September 2006.</ref> Within Abelisauridae is the subgroup '''Carnotaurinae''', and among carnotaurines, ''Aucasaurus'' and ''Carnotaurus'' are united in '''Carnotaurini'''.
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.<ref name="novas1997">Novas, F.E. (1997). "Abelisauridae". In: Currie, P.J. & Padian, K.P. ''Encyclopedia of Dinosaurs''. San Diego: Academic Press. Pp. 1–2 ISBN 0122268105.</ref><ref name="sereno1998">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.</ref> 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''.<ref name="wilsonetal2003"/> The node-based definition would not include animals like ''[[Rugops]]'' or ''[[Ilokelesia]]'', which are thought to be more [[Basal (phylogenetics)|basal]] than ''Abelisaurus'' and would be included by a stem-based definition.<ref name="taxonsearch">Sereno, P.C. (2005). [http://www.taxonsearch.org/dev/taxon_edit.php?Action=View&tax_id=6 Abelisauridae]. TaxonSearch. 7 November 2005. Retrieved 19 September 2006.</ref> Within Abelisauridae is the subgroup '''Carnotaurinae''', and among carnotaurines, ''Aucasaurus'' and ''Carnotaurus'' are united in '''Carnotaurini'''.


Many abelisaurid skull features are shared with [[carcharodontosaurid]]s. 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.<ref name="novas1997"/> 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 [[Allosauroidea|allosauroids]], respectively.<ref name="tykoskirowe2004"/>
Many abelisaurid skull features are shared with [[carcharodontosaurid]]s. 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.<ref name="novas1997"/> 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 [[Allosauroidea|allosauroids]], respectively.<ref name="tykoskirowe2004"/>
Line 72: Line 72:
***''[[Carnotaurus]]'' (Argentina)
***''[[Carnotaurus]]'' (Argentina)


''Indosaurus'' may be a [[junior synonym]] of ''Indosuchus''.<ref name="novasetal2004">Novas, F.E., Agnolin, F.L., & Bandyopadhyay, S. (2004). "Cretaceous theropods from India: a review of specimens described by Huene and Matley (1933)". ''Revista del Museo Argentino del Ciencias Naturales'' 6(1): 67–103.</ref> In addition, some scientists include ''[[Xenotarsosaurus]]'' from Argentina and ''[[Compsosuchus]]'' from India as basal abelisaurids, while others consider them to be outside Abelisauroidea. The [[France|French]] ''[[Genusaurus]]'' and ''[[Tarascosaurus]]'' have also been called abelisaurids but both are fragmentary and may be more basal ceratosaurians.<ref name="tykoskirowe2004"/>
''Indosaurus'' may be a [[junior synonym]] of ''Indosuchus''.<ref name="novasetal2004">Novas, F.E., Agnolin, F.L., & Bandyopadhyay, S. (2004). "Cretaceous theropods from India: a review of specimens described by Huene and Matley (1933)". ''Revista del Museo Argentino del Ciencias Naturales'' 6(1): 67–103.</ref> Some scientists include ''[[Xenotarsosaurus]]'' from Argentina as a basal abelisaurid,<ref name="Rauhut">Rauhut, O.W.M. (2003). "The interrelationships and evolution of basal theropod dinosaurs". ''Special Papers in Palaeontology'' 69:1-213</ref> while others consider this genus to be outside Abelisauroidea.<ref name="MartinezNovas">Martínez, R.D. and Novas, F.E. (2006). "''Aniksosaurus darwini gen. et sp. nov''., a new coelurosaurian theropod from the early Late Cretaceous of central Patagonia, Argentina". ''Revista del Museo Argentino de Ciencias Naturales'', nuevo serie 8(2):243-259</ref> The [[France|French]] ''[[Genusaurus]]'' and ''[[Tarascosaurus]]'' have also been called abelisaurids but both are fragmentary and may be more basal ceratosaurians.<ref name="tykoskirowe2004"/>


===Phylogeny===
===Phylogeny===
Line 107: Line 107:


''Ilokelesia'' was originally described as a sister group to Abelisauroidea.<ref name="coriasalgado1998">Coria, R.A. & Salgado, L. "A basal Abelisauria Novas 1992 (Theropoda-
''Ilokelesia'' was originally described as a sister group to Abelisauroidea.<ref name="coriasalgado1998">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]</ref> However, Sereno tentatively places it closer to ''Abelisaurus'' than to noasaurids, a result which agrees with several other recent analyses.<ref name="tykoskirowe2004"/><ref name="coriaetal2002"/><ref name="calvoetal2004">Calvo, J.O., Rubilar-Rogers, D., & Moreno, K. (2004). "A new Abelisauridae (Dinosauria: Theropoda) from northwest Patagonia". ''Ameghiniana'' 41(4): 555–563.</ref> 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 it was not included in Sereno's analysis. However, an independent analysis, performed by [[Jorge Calvo]] and colleagues, shows it to be an abelisaurid.<ref name="calvoetal2004"/>
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]</ref> However, Sereno tentatively places it closer to ''Abelisaurus'' than to noasaurids, a result which agrees with several other recent analyses.<ref name="tykoskirowe2004"/><ref name="coriaetal2002"/><ref name="calvoetal2004">Calvo, J.O., Rubilar-Rogers, D., & Moreno, K. (2004). "A new Abelisauridae (Dinosauria: Theropoda) from northwest Patagonia". ''Ameghiniana'' 41(4): 555–563.</ref> 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 it was not included in Sereno's analysis. However, an independent analysis, performed by Jorge Calvo and colleagues, shows it to be an abelisaurid.<ref name="calvoetal2004"/>


==Evolution==
==Evolution==
Abelisauroids are typically regarded as a Cretaceous group, although possible abelisauroid remains are known from the Middle [[Jurassic]] of Madagascar.<ref name="maganucoetal2005">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.</ref> 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 (''Majungasaurus''), which were closely connected for much of the Cretaceous. It was thought that the absence of abelisaurids from continental Africa indicated that the group [[evolution|evolved]] after the separation of Africa from Gondwana, around 100 [[million years ago]].<ref name="sampsonetal1998">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.</ref> However, the discovery of ''Rugops'' and other abelisaurid material from the middle of the Cretaceous in northern Africa disproved this hypothesis.<ref name="serenoetal2004"/><ref name="mahler2005">Mahler, L. (2005). "Record of Abelisauridae (Dinosauria: Theropoda) from the Cenomanian of Morocco". ''Journal of Vertebrate Paleontology'' 25(1): 236–239.</ref> Mid-Cretaceous abelisaurids are now known from South America as well, showing that the group existed prior to the breakup of Gondwana.<ref name="coriasalgado1998"/><ref name="calvoetal2004"/><ref name="lamannaetal2002">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.</ref>
Abelisauroids are typically regarded as a Cretaceous group, although possible abelisauroid remains are known from the Middle [[Jurassic]] of Madagascar.<ref name="maganucoetal2005">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.</ref> 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 (''Majungasaurus''), which were closely connected for much of the Cretaceous. It was thought that the absence of abelisaurids from continental Africa indicated that the group [[evolution|evolved]] after the separation of Africa from Gondwana, around 100 [[million years ago]].<ref name="sampsonetal1998">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.</ref> However, the discovery of ''Rugops'' and other abelisaurid material from the middle of the Cretaceous in northern Africa disproved this hypothesis.<ref name="serenoetal2004"/><ref name="mahler2005">Mahler, L. (2005). "Record of Abelisauridae (Dinosauria: Theropoda) from the Cenomanian of Morocco". ''Journal of Vertebrate Paleontology'' 25(1): 236–239.</ref> Mid-Cretaceous abelisaurids are now known from South America as well, showing that the group existed prior to the breakup of Gondwana.<ref name="coriasalgado1998"/><ref name="calvoetal2004"/><ref name="lamannaetal2002">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.</ref>


==References==
==References==

Revision as of 09:07, 23 November 2007

Abelisauridae
Temporal range: Jurassic? – Cretaceous
Carnotaurus.
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Sauropsida
Superorder:
Dinosauria
Order:
Saurischia
Suborder:
Theropoda
Infraorder:
Ceratosauria
Superfamily:
Abelisauroidea
Family:
Abelisauridae

Genera

Abelisauridae (meaning "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 ft) in length, from snout to tip of tail.

Anatomy

Complete skeletons have been described only for the most derived abelisaurids (Carnotaurus and Aucasaurus), making it difficult to establish 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.[1]

Reconstructed Abelisaurus skull featured in the traveling "Dinosaurs of Patagonia" exhibit. Note the rough bone surfaces and projections from the lacrimal and postorbital bones into the eye socket.

Although skull proportions varied, abelisaurid skulls were generally very tall and often very short. In Carnotaurus, for example, the skull was nearly as tall as it was long. The premaxilla in abelisaurids was very tall, so the front of the snout was blunt, not tapered as seen in many other theropods. The lacrimal and postorbital bones projected into the eye socket from the front and back, nearly dividing it into two compartments. The eye would have been located in the upper compartment of the orbit, which was tilted slightly outwards in Carnotaurus, perhaps providing some degree of binocular vision. The lacrimal and postorbital also met above the orbit, to form a pronounced ridge or brow above the eye. Extensive sculpturing is seen on many of the skull bones, in the form of long grooves, pits and protrusions. Like other ceratosaurs, the frontal bones of the skull roof were fused together. Carnotaurine abelisaurids commonly had bony projections from the frontals. Carnotaurus had two pronounced horns on the frontals, projecting laterally above the eyes, while its close relative Aucasaurus had smaller projections in the same area. Majungasaurus and Rajasaurus had a single bony horn or dome, projecting upwards from the fused frontals. These projections, like the horns of many modern animals, might have been displayed for species recognition or intimidation.[1][2][3]

The forelimbs are known only in the carnotaurine abelisaurids, Aucasaurus and Carnotaurus, in which they were vestigial. The radius and ulna were extremely short, only 25% of the length of the humerus in Carnotaurus and 33% in Aucasaurus. Typically for ceratosaurs, the carnotaurine hand contained four digits. However, it is there that any similarity ends. No wrist bones existed, with the four metacarpals articulating directly with the radius and ulna. There were no phalanges on the first or fourth digits, one on the second digit and two on the third digit. The forelimbs do not appear to have borne claws. It is unknown if this peculiar forelimb morphology applies to other abelisaurids, as their forelimbs have not been discovered.[4] Abelisaurid hindlimbs were more typical of ceratosaurs, with the astragalus and upper ankle bones fused to each other and to the tibia, forming a tibiotarsus. The tibia was shorter than the femur, giving the hindlimb stocky proportions. There were three functional digits on the foot (the second, third, and fourth), while the first digit, or hallux, did not contact the ground.[1]

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.[5]

Carnotaurus sastrei life restoration.

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.[6][7] 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.[3] 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.[8] 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.[6] 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.[1]

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.[9] Some scientists include Xenotarsosaurus from Argentina as a basal abelisaurid,[10] while others consider this genus to be outside Abelisauroidea.[11] The French Genusaurus and Tarascosaurus have also been called abelisaurids but both are fragmentary and may be more basal ceratosaurians.[1]

Phylogeny

A 2004 phylogenetic analysis, performed by Paul Sereno of the University of Chicago and several colleagues, obtained the following results:[12]

 Abelisauroidea 

Noasauridae

 Abelisauridae 

?Ilokelesia

Rugops

<font color="white">unnamed

Abelisaurus

 Carnotaurinae 

Rajasaurus

<font color="white">unnamed

Ilokelesia was originally described as a sister group to Abelisauroidea.[13] However, Sereno tentatively places it closer to Abelisaurus than to noasaurids, a result which agrees with several other recent analyses.[1][4][14] 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 it was not included in Sereno's analysis. However, an independent analysis, performed by Jorge Calvo and colleagues, shows it to be an abelisaurid.[14]

Evolution

Abelisauroids are typically regarded as a Cretaceous group, although possible abelisauroid remains are known from the Middle Jurassic of Madagascar.[15] 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 (Majungasaurus), 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.[16] However, the discovery of Rugops and other abelisaurid material from the middle of the Cretaceous in northern Africa disproved this hypothesis.[12][17] Mid-Cretaceous abelisaurids are now known from South America as well, showing that the group existed prior to the breakup of Gondwana.[13][14][18]

References

  1. ^ a b c d e f Tykoski, R.S. & Rowe, T. (2004). "Ceratosauria". In: Weishampel, D.B., Dodson, P., & Osmolska, H. (Eds.) The Dinosauria (2nd edition). Berkeley: University of California Press. Pp. 47–70 ISBN 0-520-24209-2
  2. ^ 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 to Science of the Natural History Museum of Los Angeles County 416: 1–42.
  3. ^ a b 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 of the Museum of Palaeontology of the University of Michigan 31: 1–42.
  4. ^ a b Coria, R.A., Chiappe, L.M. & Dingus, L. (2002). "A close relative of Carnotaurus sastrei Bonaparte 1985 (Theropoda: Abelisauridae) from the Late Cretaceous of Patagonia". Journal of Vertebrate Palaeontology 22: 460–465.
  5. ^ 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]
  6. ^ a b Novas, F.E. (1997). "Abelisauridae". In: Currie, P.J. & Padian, K.P. Encyclopedia of Dinosaurs. San Diego: Academic Press. Pp. 1–2 ISBN 0122268105.
  7. ^ 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.
  8. ^ Sereno, P.C. (2005). Abelisauridae. TaxonSearch. 7 November 2005. Retrieved 19 September 2006.
  9. ^ Novas, F.E., Agnolin, F.L., & Bandyopadhyay, S. (2004). "Cretaceous theropods from India: a review of specimens described by Huene and Matley (1933)". Revista del Museo Argentino del Ciencias Naturales 6(1): 67–103.
  10. ^ Rauhut, O.W.M. (2003). "The interrelationships and evolution of basal theropod dinosaurs". Special Papers in Palaeontology 69:1-213
  11. ^ Martínez, R.D. and Novas, F.E. (2006). "Aniksosaurus darwini gen. et sp. nov., a new coelurosaurian theropod from the early Late Cretaceous of central Patagonia, Argentina". Revista del Museo Argentino de Ciencias Naturales, nuevo serie 8(2):243-259
  12. ^ a b 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.
  13. ^ a b 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]
  14. ^ a b c Calvo, J.O., Rubilar-Rogers, D., & Moreno, K. (2004). "A new Abelisauridae (Dinosauria: Theropoda) from northwest Patagonia". Ameghiniana 41(4): 555–563.
  15. ^ 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.
  16. ^ 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.
  17. ^ Mahler, L. (2005). "Record of Abelisauridae (Dinosauria: Theropoda) from the Cenomanian of Morocco". Journal of Vertebrate Paleontology 25(1): 236–239.
  18. ^ 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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