Like most theropods, abelisaurids werecarnivorousbipeds. They were characterized by stocky hind limbs and extensive ornamentation of theskull bones, with grooves and pits. In many abelisaurids, such asCarnotaurus, the forelimbs arevestigial, the skull is shorter, and bony crests grow above the eyes. Most of the known abelisaurids would have been between 5 and 9 m (17 to 30 ft) in length, from snout to tip of tail, with a new and as yet unnamed specimen from northwestern Turkana in Kenya, Africa reaching a possible length of 11–12 m (36 to 39 ft).[6] Before becoming well known, fragmentary abelisaurid remains were occasionally misidentified as possible South Americantyrannosaurids.[7]
Size comparison of five abelisaurids;Carnotaurus,Ekrixinatosaurus,Skorpiovenator,Aucasaurus, andMajungasaurus
Abelisaurid hind limbs were more typical of ceratosaurs, with theastragalus andcalcaneum (upper ankle bones) fused to each other and to thetibia, forming a tibiotarsus. The tibia was shorter than thefemur, giving the hind limb stocky proportions. Three functional digits were on the foot (the second, third, and fourth), while the first digit, orhallux, did not contact the ground.[8]
Although skull proportions varied, abelisaurid skulls were generally very tall and very short in length. InCarnotaurus, for example, the skull was nearly as tall as it was long. Thepremaxilla in abelisaurids was very tall, so the front of the snout was blunt, not tapered as seen in many other theropods.[6]
Two skull bones, thelacrimal andpostorbital bones, projected into theeye socket from the front and back, nearly dividing it into two compartments. The eye would have been located in the upper compartment, which was tilted slightly outwards inCarnotaurus, perhaps providing some degree ofbinocular vision. The lacrimal and postorbital also met above the eye socket, to form a ridge or brow above the eye.[6]
Sculpturing is seen on many of the skull bones, in the form of long grooves, pits, and protrusions. Like otherceratosaurs, thefrontal bones of the skull roof were fused together. Carnotaurines commonly had bony projections from the skull.Carnotaurus had two pronounced horns, projecting outward above the eyes, while its close relativeAucasaurus had smaller projections in the same area.Majungasaurus andRajasaurus had a single bony horn or dome, projecting upwards from the skull. These projections, like the horns of many modern animals, might have beendisplayed for species recognition or intimidation.[8][9][10] InArcovenator, the dorsal margin of the postorbital (and probably also the lacrimal) is thickened dorsolaterally, forming a strong and rugose bony brow ridge rising above the level of the skull roof.[3] Possibly, this rugose brow ridge supported a keratinous or scaly structure for displays.
Hand bones ofCarnotaurus, as interpreted by Ruiz and colleagues (2011)[11]
Data for the abelisaurid fore limbs are known fromEoabelisaurus and the carnotaurinesAucasaurus,Carnotaurus, andMajungasaurus. All had small fore limbs, which seem to have been vestigial.[12] The bones of the forearm (radius andulna) were extremely short, only 25% of the length of the upper arm (humerus) inCarnotaurus and 33% inAucasaurus. The entire arm was held straight, and the elbow joint was immobile.[12]
As is typical for ceratosaurs, the abelisauridhand had four basic digits, but any similarity ends there. Nowrist bones existed, with the four palm bones (metacarpals) attaching directly to the forearm. Nophalanges (finger bones) were on the first or fourth digits, only one on the second digit and two on the third digit. These two external fingers were extremely short and immobile. Manual claws were very small inEoabelisaurus, and totally absent in carnotaurines.[12]
More primitive relatives such asNoasaurus andCeratosaurus had longer, mobile arms with fingers and claws.[13] Paleobiologist Alexander O. Vargas suggested a major reason for the evolution towards vestigial fore limbs in the group was because of a genetic defect; the loss of function in HOXA11 andHOXD11, two genes that regulate the fore limbs' development.[14]
Abelisaurids are typically regarded as a Cretaceous period group. The earliest possible abelisaurid taxon isEoabelisaurus mefi from theJurassic period of Argentina,[15] though other researchers either consider it as a ceratosaurid, an abelisauroid or its sister taxon outside abelisaurids.[16][17][18] Indeterminate remains are also known from theJurassic period of Madagascar andTanzania.[19][20][21] Abelisaurid remains are mainly known in the southern continents, which once made up thesupercontinent ofGondwana. When first described in 1985, onlyCarnotaurus andAbelisaurus were known, both from theLate Cretaceous ofSouth America. Abelisaurids were then located in LateCretaceousIndia (Indosuchus andRajasaurus) andMadagascar (Majungasaurus), which were closely connected for much of the Cretaceous. It was thought that the absence of abelisaurids from continentalAfrica indicated that the groupevolved after the separation of Africa from Gondwana, around 100million years ago.[22] However, the discovery ofRugops and other abelisaurid material from the middle of the Cretaceous in northern Africa disproved this hypothesis.[23][24] Mid-Cretaceous abelisaurids are now known from South America as well, showing that the group existed prior to the breakup of Gondwana.[25][26][27] In 2014, the description ofArcovenator escotae from southernFrance provided the first indisputable evidence of the presence of Abelisaurids inEurope.Arcovenator presents strong similarities with the MadagascanMajungasaurus and Indian abelisaurids, but not with the South American forms.Arcovenator,Majungasaurus, and Indian forms are united in the new cladeMajungasaurinae.[3]
PaleontologistsJose Bonaparte andFernando Novas coined the name Abelisauridae in 1985 when they described the eponymousAbelisaurus. The name is formed from the family name of Roberto Abel, who discoveredAbelisaurus, and from theGreek wordσαυρος (sauros) meaning lizard. The very common suffix-idae is usually applied tozoologicalfamily names and is derived from the Greek suffix -ιδαι (-idai) meaning 'descendants'.[28]
Abelisauridae is a family in rank-basedLinnaean taxonomy, within theinfraorderCeratosauria and the superfamilyAbelisauroidea, which also contains the familyNoasauridae. It has had several definitions inphylogenetic taxonomy. It was originally defined as a node-basedtaxon includingAbelisaurus,Carnotaurus, their common ancestor, and all of its descendants.[29][30]
Later, it was redefined as a stem-based taxon, including all animals more closely related toAbelisaurus (or the more completeCarnotaurus) than toNoasaurus.[10] The node-based definition would not include animals such asRugops orIlokelesia, which are thought to be morebasal thanAbelisaurus and would be included by a stem-based definition.[31] Within the Abelisauridae is the subgroupCarnotaurinae, and among carnotaurines,Aucasaurus andCarnotaurus are united inCarnotaurini.[23]
Skeletal diagram of the known material ofCarnotaurus
Complete skeletons have been described only for the most advanced abelisaurids (such asCarnotaurus andAucasaurus), making establishment ofdefining features of the skeleton for the family as a whole more difficult. However, most are known from at least some skull bones, so known shared features come mainly from the skull.[8] Many abelisaurid skull features are shared withcarcharodontosaurids. 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.[29] However, nocladistic analysis has ever found such a relationship, and aside from the skull, abelisaurids and carcharodontosaurids are very different, more similar to ceratosaurs andallosauroids, respectively.[8]
Ilokelesia was originally described as a sister group to the Abelisauroidea.[25] However, Sereno tentatively places it closer toAbelisaurus than to noasaurids, a result which agrees with several other recent analyses.[8][26][32] If a stem-based definition is used,Ilokelesia andRugops are therefore basal abelisaurids. However, as they are more basal thanAbelisaurus, they are outside of the 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.[26]
Some scientists includeXenotarsosaurus from Argentina andCompsosuchus from India as basal abelisaurids,[33][34] while others consider them to be outside the Abelisauroidea.[35] TheFrenchGenusaurus andTarascosaurus have also been called abelisaurids but both are fragmentary and may be more basal ceratosaurians,[8] though Tortosaet al. (2014) considered both to be distinct abelisaurids.[3] Subsequent phylogenetic analyses recoverXenotarsosaurus andTarascosaurus as an abelisaurid,[36][37] butGenusaurus as either a noasaurid or an abelisaurid.[38][39][40]
Skeleton ofEoabelisaurus, a close relative of the Abelisauridae
With the description ofSkorpiovenator in 2008, Canaleet al. published another phylogenetic analysis focusing on the South American abelisaurids. In their results, they found that all South American forms, includingIlokelesia (exceptAbelisaurus), grouped together as a subclade of carnotaurines, which they named theBrachyrostra.[41] In the same year Matthew T. Carrano and Scott D. Sampson published new large phylogenetic analysis of ceratosaurian.[42] With the description ofEoabelisaurus, Diego Pol and Oliver W. M. Rauhut (2012) combined these analyses and added 10n new characters. The followingcladogram follows their analysis.[43]
Dental microwear features of abelisaurid teeth from theMarília Formation of Brazil indicate that they predated heavily on large prey.[45] Fossil teeth found amid the bones of a titanosaur from theAllen Formation of Argentina suggest that abelisaurids preyed upon or at least scavenged titanosaurs.[46]
Studies of the abelisauridMajungasaurus indicate that it was a much slower-growing dinosaur than other theropods, taking nearly 20 years to reach adult size.[47] However, other mature abelisaurid specimens indicate that they generally reached a faster rate of maturation. The holotype ofAucasaurus had a minimum age of 11 years,[48] the holotype ofNiebla had a minimum age of 9 years,[49] and MMCh-PV 69 had a minimum age of 14 years.[50]
^Hendrickx, Christophe; Mateus, Octávio (2014). "Abelisauridae (Dinosauria: Theropoda) from the Late Jurassic of Portugal and dentition-based phylogeny as a contribution for the identification of isolated theropod teeth".Zootaxa.3759:1–74.doi:10.11646/zootaxa.3759.1.1.PMID24869965.S2CID12650231.
^abcdeTortosa, Thierry; Buffetaut, Eric; Vialle, Nicolas; Dutour, Yves; Turini, Eric; Cheylan, Gilles (2014). "A new abelisaurid dinosaur from the Late Cretaceous of southern France: Palaeobiogeographical implications".Annales de Paléontologie.100:63–86.Bibcode:2014AnPal.100...63T.doi:10.1016/j.annpal.2013.10.003.
^"Abelisaurus." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B.The Age of Dinosaurs. Publications International, LTD. p. 105.ISBN0-7853-0443-6.
^abcdefTykoski, 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. 47–70ISBN0-520-24209-2
^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 in Science of the Natural History Museum of Los Angeles County.416:1–42.
^abWilson, 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.
^Agnolin, Federico L.; Chiarelli, Pablo (2009). "The position of the claws in Noasauridae (Dinosauria: Abelisauroidea) and its implications for abelisauroid manus evolution".Paläontologische Zeitschrift.84 (2): 293.doi:10.1007/s12542-009-0044-2.S2CID84491924.
^abCoria, 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]
^abcCalvo, J.O.; Rubilar-Rogers, D.; Moreno, K. (2004). "A new Abelisauridae (Dinosauria: Theropoda) from northwest Patagonia".Ameghiniana.41 (4):555–563.
^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]
^abNovas, F.E. (1997). "Abelisauridae". In: Currie, P.J. & Padian, K.P.Encyclopedia of Dinosaurs. San Diego: Academic Press. Pp. 1–2ISBN0-12-226810-5.
^Sereno, P.C. (1998). "A rationale for phylogenetic definitions, with applications to the higher-level taxonomy of Dinosauria".Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen.210:41–83.doi:10.1127/njgpa/210/1998/41.
^Coria, R.A.; Chiappe, L.M.; Dingus, L. (2002). "A close relative ofCarnotaurus sastrei Bonaparte 1985 (Theropoda: Abelisauridae) from the Late Cretaceous of Patagonia".Journal of Vertebrate Paleontology.22 (2):460–465.doi:10.1671/0272-4634(2002)022[0460:ANCROC]2.0.CO;2.S2CID131148538.
^Rauhut, O.W.M. (2003). "The interrelationships and evolution of basal theropod dinosaurs".Special Papers in Palaeontology.69:1–213.
^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
^Leonardo S. Filippi; Ariel H. Méndez; Rubén D. Juárez Valieri; Alberto C. Garrido (2016). "A new brachyrostran with hypertrophied axial structures reveals an unexpected radiation of latest Cretaceous abelisaurids".Cretaceous Research.61:209–219.Bibcode:2016CrRes..61..209F.doi:10.1016/j.cretres.2015.12.018.hdl:11336/149906.
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