Abelisauridae

Skeletal reconstruction of Aucasaurus garridoi

• South America
• Africa and Madagascar
• India

The Abelisauridae are a group of theropod dinosaurs within the Ceratosauria. It was medium to large, bipedal carnivores, which were characterized by relative short arms and a short and tall, heavily ornamented skull.

Fossils are from the Lower and Upper Cretaceous ( Aptian to Maastrichtian ) of Africa, Madagascar, South America and India.

• 2.1 Outer systematics and definitions
• 2.2 Internal systematics

• 5.1 Literature Used
• 5.2 Notes and references

Features

The skull was built robust overall, with various skull bones were reinforced fused together, such as the paired nasal bone ( nasal ) and the paired frontal bone ( frontal ). The skull was disproportionately high and short. This feature was extremely trained in Carnotaurus, where the skull was almost as high as long. The premaxillary bone ( premaxilla ), one situated in front of the upper jaw ( maxilla ) bone, was relatively high, which makes the muzzle from the side appears dull. Even when viewed from above, the muzzle was relatively broad and rounded, not pointed as in many other theropods.

The surface of the facial skeleton was heavily ornamented with numerous pits and protrusions, indicating that the integument was horny. About the eye socket (orbit ) was a thickened Brauenwulst, bounded by the lacrimal bone ( lacrimal ) and the postorbital is formed. Various genres show emanating from the skull horns or appendages: So Rajasaurus and Majungasaurus have a single, low horn, which is formed by the nasal bones and the frontal bone and recalls the skull domes of Pachycephalosauria. Aucasaurus other hand, shows a pair of small projections emanating from the frontal bone, while Carnotaurus a pair of very large brow horns is formed.

As with other theropod skull had several cranial window. The Infra pace Ralf Rochester, located behind the eye socket (orbit ) was great as with other representatives of the Ceratosauria - often was this skull window twice as large as the eye socket. The lower jaw is characterized by a large Mandibularfenster formed from the dental, and the front part of the tooth-bearing lower jaw, as well as from the rear jaw. This enlarged cranial window was accompanied by a reduction of the contact points between dental and rear jaw bone and probably led to one another in an increased mobility of the bone of the mandible. The eye sockets appear teardrop-shaped, while the Antorbitalfenster, the cranial window located between the eye socket and nostril, was shortened.

The teeth were relatively small, laterally flattened and show serrated cutting edges. While the paired premaxillary leg on each side has four teeth in all Abelisauriden varies the number of teeth in the upper jaw of 12 for Carnotaurus to 19 at Rugops.

Postcranial skeletons

The neck was built to last. The cervical ribs showed rod-like, rearward extensions which - served as the approach surface for a comparatively strong neck muscles - in combination with an enlarged occipital ( occiput ) to the skull back. The caudal vertebrae of some representatives of Abelisauridae exhibited a unique morphology: So the transverse processes were - lateral outgrowths of the vertebrae - long and steep upward. This probably was space for an enlarged musculus caudofemoralis available - the prime mover muscles of the legs. The transverse processes also stood with the transverse processes of adjacent vertebrae in combination, indicating that the tail was immovable as in other theropods. Evidence of these specialized tail characteristics are found in the South American representatives of Abelisauride so in Carnotaurus, Aucasaurus, Skorpiovenator and Ilokelesia, but absent in Abelisauriden from Madagascar and India.

The arms are only narrated by Aucasaurus, Carnotaurus and Majungasaurus. In these genera, the arms were formed only rudimentary. Of the humerus and attaches Aucasaurus Carnotaurus only about 30 % of the length of the femur. The forearm showed more than a third of the length of the upper arm and was extremely short. The arm was always kept straight because the elbow joint was immobile. The metacarpal bones ( metacarpals ) steered directly to the forearm; Carpal bones ( carpal bones ) were missing. The hand was as with other representatives of the Ceratosauria of four rays, but showed a very unusual anatomy of theropod: were missing finger bones at the first and fourth jet - only the two central rays show two extremely shortened fingers. The responsible for the transmission of stimuli, leading to poor nerve fibers were similar greatly reduced as in recent emus and kiwis, where the arms have become functionless.

The basin was characterized by an elongated ilium ( ilium ). In various representatives of Abelisauridae steered a rearwardly Knochenast the ilium with the transverse process of the first caudal vertebra - an unusual feature for theropods. The hind legs are similar to those of basal theropods such as Ceratosaurus and were proportionally short and stocky with most genres. Usually, the shinbone ( tibia ) and the fibula ( fibula ) and the upper tarsal bones was merged ( the astragalus and the calcaneus ) to a so-called Tibiotarsus - the tibiotarsus was there shorter than the upper thigh bone (femur).

System

Outer systematics and definitions

Coelophysoidea

Tetanurae

Ceratosaurus

Noasauridae

Abelisauridae

The Abelisauridae is counted among the Ceratosauria, a group that has already split off early from the lineage leading to birds and thus occupies a basal ( original ) position within the theropods. The Abelisauridae are the most derived ( advanced ) group of Ceratosauria. Within the Ceratosauria the Abelisauridae forms the sister group of the Noasauridae - these two groups as well as various basal representatives are summarized in the group Abelisauroidea.

For the Abelisauridae are different phylogenetic definitions. Initially this group was as node-based taxon (node ​​based definition) defined: To include this taxon example, according to Sereno (1998), the last common ancestor of Abelisaurus and Carnotaurus, and all descendants of that ancestor. However, this definition includes representatives such as the Rugops described only in 2004, which are classified as basal as Abelisaurus to from the Abelisauridae. Wilson and colleagues ( 2003) therefore published a new stem line-based definition ( system based definition): According to this definition include the Abelisauridae all taxa with a, with the Carnotaurus sastrei than Noasaurus leali ( a representative of the Noasauridae ) were more closely related.

The definition of this group by jointly derived characteristics ( synapomorphies ) - characteristics by which this taxon differs from all related taxa - is difficult. Thus, most representatives are known only by very fragmentary skeletal remains, and it is unclear whether certain features were really limited to the Abelisauridae, Upper already appeared in more basal, standing outside this group forms. Putative synapomorphies are found mainly in the skull bones, and include, for example, the short and deep Zwischenkieferbein the thick paired frontal bone and the reduced contacts between the bones of the lower jaw with a.

Inside systematics

Rugops

Abelisaurus

Majungasaurus

Carnotaurus

Aucasaurus

Ilokelesia

Skorpiovenator

Ekrixinatosaurus

About the relationships within the Abelisauridae there is currently no consensus. In most phylogenetic analyzes, however Abelisaurus is considered a basal member of the group, while Carnotaurus occupies a derived position. To summarize the derived representatives of Abelisauridae, the group Carnotaurinae is often used, which includes all Abelisauriden that are more closely related to Carnotaurus than Abelisaurus. Carrano and Sampson (2008), however, come to the conclusion that Abelisaurus was not basal, but a derived representative of Abelisauridae.

Juan Canale and colleagues ( 2009) propose a new group within the Carnotaurinae that Brachyrostra. This group aims to summarize all Carnotaurinen which have a proportionally very short snout ( Carnotaurus, Aucasaurus, Ilokelesia, Skorpiovenator and Ekrixinatosaurus ) and includes Majungasaurus than basal representatives showing a proportionally longer snout. Other researchers see Majungasaurus but as the next of kin of Carnotaurus and thus as a very secondary representative.

Temporal distribution and paleobiogeography

Previous findings are limited to the Cretaceous period - the oldest forms Kryptops Fund from the Late Cretaceous ( Aptian ) of Africa. However, Simone Maganuco and colleagues ( 2004) describe teeth from the Middle Jurassic of Madagascar attributable possibly the Abelisauridae According to these researchers. The last known representative of the Abelisauridae come from the latest Cretaceous ( Maastrichtian ) of India and Madagascar and died only at the Cretaceous - Paleogene extinction event together with all other non-avian dinosaurs from.

Geographically undoubted discoveries on South America, India, Madagascar and continental Africa are limited. These land masses once formed the southern Gondwana supercontinent, which gradually broke during the Cretaceous period in its current constituents. The exact sequence of this break-up is still a matter of much debate, with the Abelisauriden - as one of those groups that distinguish the Gondwana faunas of the faunas of the northern continent Laurasia United - play an important role in the chain of arguments of the competing hypotheses. A common hypothesis, called the Africa -first hypothesis, assumes that Africa already completely severed during the Lower Cretaceous of the other landmasses of Gondwana, while the latter were still up in the Upper Cretaceous in through land bridges connected. An important argument in support of this hypothesis, the distribution of Abelisauriden was used, whose remains were found frequently in India, Madagascar and South America, in Africa, however, were missing for a long time, which indicated that evolved the Abelisauridae only after the separation of Africa from the rest of Gondwana have. This argument has recently been called into question, as with Rugops a Abelisauride in continental Africa was discovered and particularly since ancient finds from South America appeared to be dated to a time when Africa was not yet separated. Supporters of the hypothesis noted, however, that Rugops was a very basal representatives of Abelisauridae, and that the typical for the rest of Gondwana -derived members of the group are still missing.

History of Research

, 1985 Jose Bonaparte and Fernando Novas one discovered in Argentina skull as Abelisaurus. Since Abelisaurus significantly different from all other then known theropods, these researchers a new group featured on the Abelisauridae, which initially contained Abelisaurus as a single genus. The names Abelisaurus and Abelisauridae honor Roberto Abel, director of the Museo de Cipolleti and discoverer of the skull. The Abelisauridae was initially classified within the Carnosauria, a group that were then attributed almost all Großtheropoden. Only in the early 90s, today's classification within the Ceratosauria able to establish itself.

Shortly after the description of the group more representative were discovered. So Bonaparte described in the same year (1885 ) the new genus Carnotaurus as the second known member of this group. Carnotaurus is based on a well-preserved, nearly complete skeleton was also discovered in Argentina. Martinez and colleagues described a year later a far fragmentarischeren, also built in Argentina Fund as Xenotarsosaurus. In a likewise published in 1986 publication Bonaparte believed that it could also act at the Indosuchus discovered in India around a Abelisauriden. Although known only from two skull, pointed this find out that the Abelisauridae were not confined to South America.

To date, numerous other representatives of Abelisauridae have been described. Although a majority of these species is known only by very fragmentary remains of two skeletons were described recently with Aucasaurus and Skorpiovenator that are similar to well preserved as that of Carnotaurus. Excavations that take place in Madagascar since 1993, brought numerous skeletons of Abelisauriden Majungasaurus revealed - today this species is regarded as one of the best- known theropods of the southern landmasses ( Gondwana ).

Documents

Used literature

• JI Canale, CA Scanferla, FL Agnolin and FE Novas: New carnivorous dinosaur from the Late Cretaceous of NW Patagonia and the evolution of abelisaurid theropods. In: Natural Sciences. Vol 96, No. 3, 2009, pp. 409-414, doi: 10.1007/s00114-008-0487-4.
• Matthew Carrano, Scott Sampson: The Phylogeny of Ceratosauria ( Dinosauria: Theropoda ). In: Journal of Systematic Palaeontology. 6, 2008, pp. 183-236.
• P. Senter: Vestigial skeletal structures in dinosaurs. In: Journal of Zoology. 280, No. 1, 2010, pp. 60-71, doi: 10.1111/j.1469-7998.2009.00640.x.
• R. S. Tykoski, T. Rowe: Ceratosauria. In: DB Weishampel, P. Dodson, H. Osmólska (eds.): The Dinosauria. 2nd edition. University of California Press, Berkeley, 2004, ISBN 0-520-24209-2, pp. 47-70.
• Scott D. Sampson, Lawrence M. Witmer: Craniofacial Anatomy of Majungasaurus Crenatissimus ( Theropoda: Abelisauridae ) From the Late Cretaceous of Madagascar. In: Journal of Vertebrate Paleontology. 27, No. sp8, 2007, pp. 32-102, doi: 10.1671/0272-4634 (2007) 27 [ 32: CAOMCT ] 2.0.CO; 2
• JA Wilson, PC Sereno, S. Srivastava, DK Bhatt, A. Khosla, A. Sahni: A new abelisaurid ( Dinosauria, Theropoda ) from the Lameta Formation ( Cretaceous, Maastrichtian ) of India. In: Contributions from the Museum of Paleontology ( University of Michigan ). 31, No. 1, 2003, pp. 1-42 (PDF).
• RA Coria, LM Chiappe, L. Dingus: A new close relative of Carnotaurus sastrei Bonaparte 1985 ( Theropoda: Abelisauridae ) from the Late Cretaceous of Patagonia. In: Journal of Vertebrate Paleontology. 22, No. 2, 2002, pp. 460-465.
• Fernando E. Novas: The age of dinosaurs in South America. Indiana University Press, Bloomington 2009, ISBN 978-0-253-35289-7.
• W. Scott Persons, Philip J. Currie Dinosaur Speed ​​Demon: The Caudal musculature of Carnotaurus sastrei and Implications for the evolution of South American Abelisaurids. In: PLoS ONE. 6, No. 10, October 17, 2011, doi: . 10.1371/journal.pone.0025763. Accessed on 10 August 2012.
• PC Sereno, JA Wilson, JL Conrad: New dinosaurs link southern landmasses in the Mid - Cretaceous. In: Proceedings of the Royal Society B: Biological Sciences. 271, 1546, 2004, pp. 1325-1330, doi: 10.1098/rspb.2004.2692.
• Simone Maganuco, Andrea Cau, Giovanni Pasini: First description of theropod remains from the Middle Jurassic ( Bathonian ) of Madagascar. In: Atti della Società Italiana di Scienze naturali e del Museo Civico di Storia Naturale in Milano. 146, No. 2, 2005, pp. 165-202.
• JF Bonaparte, Novas FE (1985 ): Abelisaurus comahuensis, ng, n.sp., Carnosauria del Cretácico Tardio de Patagonia. Ameghiniana 21: 259-265. ( Translated into English by Matthew Carrano, 1998: Abelisaurus comahuensis, ng, n.sp., from the Late Cretaceous of Carnosauria Patagonia PDF. )
• JF Bonaparte: The Gondwanian theropod Families Abelisauridae and Noasauridae. In: Historical Biology. 5, Harwood Academic Publishers, 1991, pp. 1-25.
• RA Coria, LM Chiappe, L. Dingus: A new close relative of Carnotaurus sastrei Bonaparte 1985 ( Theropoda: Abelisauridae ) from the Late Cretaceous of Patagonia. In: Journal of Vertebrate Paleontology. 22, No. 2, 2002, pp. 460-465.
• David W. Krause, Scott D. Sampson, Matthew T. Carrano, Patrick M. O'Connor: Overview of the History of Discovery, Taxonomy, Phylogeny, and Biogeography of Majungasaurus Crenatissimus ( Theropoda: Abelisauridae ) From the Late Cretaceous of Madagascar. In: Journal of Vertebrate Paleontology. 27, No. sp8, 2007, pp. 1-20, doi: 10.1671/0272-4634 (2007) 27 [ 1: OOTHOD ] 2.0.CO; 2