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Abelisauroidea Temporal range: Middle Jurassic - Late Cretaceous,
Majungasaurus crenatissimus skeleton, Stony Brook University
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Clade:	†Ceratosauria
Clade:	†Neoceratosauria
Superfamily:	†Abelisauroidea Bonaparte & Novas, 1985
Families
Betasuchus Coeluroides? Dahalokely Ligabueino? Ozraptor? Orthogoniosaurus? †Abelisauridae †Noasauridae

Abelisauroidea is typically regarded as a Cretaceous group, though the earliest abelisauridae remains are known from the Middle Jurassic of Argentina (classified as the species Eoabelisaurus mefi) and possibly Madagascar (fragmentary remains of an unnamed species) possible abelisauridae remains (an isolated left tibia, right femur, and right tibia) were also discovered in Late Jurassic Tendaguru Beds in Tanzania. Abelisauroids flourished in the Southern hemisphere during the Cretaceous period, but their origins can be traced back to at least the Middle Jurassic, when they had a more global distribution (the earliest known abelisauroid remains come from Australian and South American deposits dated to about 170 million years ago). By the Cretaceous period, abelisauroids had apparently become extinct in Asia and North America, possibly due to competition from tyrannosauroids. However, advanced abelisauroids of the family Abelisauridae persisted in the southern continents until the Cretaceous–Paleogene extinction event 66 million years ago.

Discussion

In order to assess the phylogenetic position of Eoabelisaurus, the analysis places Eoabelisaurus as the most basal member of the Abelisauridae. Abelisaurid synapomorphies include the laterally covered lacrimal antorbital fossa, broad cervical prespinal fossae, anteroposteriorly short anterior caudal neural spines, absence of a ventral groove in the anterior caudals, presence of rudimentary centrodiapophyseal laminae in the anterior mid-caudals, reduced distal ginglymus in the manual phalanges, and the presence of a flexor depression in the pedal unguals. Alternative phylogenetic placements of Eoabelisaurus are significantly suboptimal, except for a slightly more basal position. Noasaurids had longer arms than their relatives the abelisaurids, whose arms were tiny and diminished. Although by no means as large or specialized as the arms of advanced bird-like theropods, Noasauridae arms were nevertheless capable of movement and use, possibly even for hunting in large-clawed genera such as Noasaurus. Some genera such as Limusaurus did have somewhat reduced arms and hands, but far from the extent that Abelisaurids acquired. Noasaurids were also nimble and lightly built, with feet showing adaptations for running such as a long central foot bone. Noasaurids varied in size, from the small Velocisaurus which was under 5 feet (1.5 meters) long, to much larger genera such as Elaphrosaurus and Deltadromeus, which were more than 20 feet (6.2 meters) in length.

Classification

Abelisauroidea is a superfamily which contains the family Noasauridae and Abelisauridae. Noasauridae was a very diverse group, with the two most complete members, Masiakasaurus and Limusaurus, showing unusual features very different from each other. Masiakasaurus had an unusually downturned jaw, with long and sharply pointed spoon-shaped teeth. Some of these teeth were nearly horizontal in orientation. Limusaurus, on the other hand, was completely toothless as an adult and likely possessed a horny beak. This large disparity means that it is difficult to find any skull features shared by members of Noasauridae as a whole. Abelisauridae remains are mainly known in the southern continents, which once made up the supercontinent of Gondwana. It has had several definitions in phylogenetic taxonomy. It was originally defined as a node-based taxon including Abelisaurus, Carnotaurus, and all of its descendants. 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.

Abelisauroidea	Noasauridae  Laevisuchus Masiakasaurus Noasaurus Velocisaurus  Abelisauridae  Eoabelisaurus Rugops Abelisaurus  Carnotaurinae  Majungasaurus Indosaurus Rajasaurus  Brachyrostra  Ilokelesia Ekrixinatosaurus Skorpiovenator  Carnotaurini  Carnotaurus Aucasaurus

Shared characteristics

Complete skeletons have been described only for the most advanced abelisauridae (such as Carnotaurus and Aucasaurus), making the establishment of defining 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. Many abelisaurid skull features are shared with carcharodontosaurids. These shared features, along with the fact that abelisauridae seem to have replaced carcharodontosauridae in South America, has led to suggestions that the two groups were related. Noasaurids were considered to be distinctive Abelisauroidea with a peculiar "sickle claw" on the second toe of the foot, convergently developed with that of Deinonychosaurians. Among Noasaurids, the Argentinean species Noasaurus leali(Lastest Cretaceous) and Ligabueino(Early Cretaceous) are known from incomplete specimens, including dissarticulated non-ungueal phalanges and in Noasaurus, a claw. A detailed overview of these elements indicates that the supposed raptorial claw of the second pedal digit actually belongs to the first or second finger of the manus, and the putative pedal non-ungual phalanges or both genera also pertain to the manus.

Discovery

Most Abelisauroid were found in Madagascar, Asia, or sometimes in Africa. Abelisauridae 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. In Madagascar, we are known as “Majungasaurus”, were discovered by Charles Depéret (French paleontologist). Majungasaurus was the most common abelisauroid which we know. Studies of the abelisauridae Majungasaurus indicate that it was a much slower-growing dinosaur than other theropods, taking nearly 20 years to reach adult size. Not only Majungasaurus was found in Madagascar but also Masiakasaurus which was the most complete fossil noasauridae found. Similar studies on other abelisaurid genera indicate that this slow maturation may have been a common trait to the whole of the Abelisauridae. Noasaurines are Late Cretaceous noasaurids known exclusively from southern continents and islands such as South America, Madagascar, and India which was an island near Madagascar during the Cretaceous. Elaphrosaurines were lightly built theropods, with small skulls and long necks and legs. If Limusaurus is any indication, adult elaphrosaurines were completely toothless, and their mouths were probably edged with a horny beak. It is likely that Limusaurus and other elaphrosaurines were primarily herbivorous as adults, due to mature Limusaurus specimens preserving gastroliths and chemical signatures resembling those of herbivorous dinosaurs. In South America, many of abelisauroids were discovered such as Skorpiovenator, Tarasscosaurus, Erikasaurus, Quilmesaurus, Aucasarus, Ilokelesia, Pycnonemosaurus etc. In Africa, we can find many abelisauroid which were Rugops, Kryptops, etc. Many abelisauroid can grow in South America, because they can evolve in a fruitful place. Kurupi itaata represents the first formally named vertebrate of the Marília Formation (Bauru Group, Bauru Basin) and one of the few theropod records for the Maastrichtian of the Bauru Basin. Its abelisauridae affinities are well-established based on the anatomy of the pelvis and anterior caudal vertebrae; however, closer relationships with other abelisauridae are still unclear. The specimens provide new information on abelisauroids which are still poorly known in the Brazilian fossil record, and on the distribution of this diverse group of theropod dinosaurs in South America. These discoveries indicate that abelisauroids were the most common large predatory dinosaurs in the outcrops where they come from.

Distribution

Abelisauroidea were common in Gondwana during the Cretaceous, but exceedingly rare in the Northern Hemisphere. The oldest definitive abelisaurids so far come from the late Early Cretaceous of South America and Africa, and the early evolutionary history of the clade is still poorly known. Here, we report a new abelisaurid from the Middle Jurassic of Patagonia, Eoabelisaurus, which predates the so far oldest known secure member of this lineage by more than 40 Million years ago. The almost complete skeleton reveals the earliest evolutionary stages of the distinctive features of abelisaurids, such as the modification of the forelimb, which started with a reduction of the distal elements. The find underlines the explosive radiation of theropod dinosaurs in the Middle Jurassic and indicates an unexpected diversity of ceratosaurs at that time. The apparent endemism of abelisauroids to southern Gondwana during Pangean times might be due to the presence of a large, central Gondwanan desert. This indicates that, apart from continent-scale geography, aspects such as regional geography and climate are important to reconstruct the biogeographical history of Mesozoic vertebrates. The diversity of Australia’s theropod fauna from the Middle-Cretaceous (Albian–Cenomanian) is distinctly biased towards the medium-sized megaraptorids, despite the preponderance of abelisauroids in the younger but latitudinally equivalent Patagonian theropod fauna. Here, we present new evidence for the presence of ceratosaurian, and specifically Abelisauroid, theropods from the Cenomanian Griman Creek Formation of Lightning Ridge, New South Wales. A partial cervical vertebra is described that bears a mediolaterally concave ventral surface of the centrum delimited by sharp ventrolateral ridges that contact the parapophyses. Among theropods, this feature has been reported only in a cervical vertebra attributed to the noasaurid Noasaurus. We also reappraise evidence recently cited against the ceratosaurian interpretation of a recently described astragalocalcaneum from the upper Barremian–lower Aptian San Remo Member of the upper Strzelecki Group in Victoria. Inclusion of the Lightning Ridge cervical vertebra and Victorian astragalocalcaneum into a revised phylogenetic analysis focused on elucidating ceratosaurian affinities reveals support for the placement of both specimens within Noasauridae, which among other characters is diagnosed by the presence of a medial eminence on the ascending process of the astragalus. The Lightning Ridge and Victorian specimens simultaneously represent the first Noasaurids reported from Australia and the astragalocalcaneum is considered the earliest known example of a Noasaurid in the world to date. The recognition of Australian Noasaurids further indicates a more widespread Gondwanan distribution of the clade outside of South America, Madagascar, and India consistent with the timing of the fragmentation of the supercontinent.

Paleobiology

Behavior

Using three methods, namely a cladistic analysis performed on a dentition-based data matrix, and discriminant and cluster analyses conducted on a large dataset of theropod teeth measurements, we identify three dental morphotypes which are confidently referred to abelisaurid theropods. Whether the morphotypes represent different abelisaurid subclades or different positional entities within the jaw of the same abelisaurid species, is unknown. Such an identification, nevertheless, provides additional evidence of abelisaurids feeding on sauropod carcasses.