Austrocheirus
| Austrocheirus | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Upper Cretaceous (Lower Maastrichtian ) | ||||||||||||
| 72 to 69.9 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Austrocheirus | ||||||||||||
| Ezcurra , Agnolin & Novas , 2010 | ||||||||||||
| species | ||||||||||||
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Austrocheirus is a genus of theropod dinosaur from the Abelisauroidea group . So far only a very fragmentary specimen is known from the late Upper Cretaceous (Lower Maastrichtian ) of Argentina . This genus was first scientifically described in 2010 by Ezcurra and colleagues with the only species Austrocheirus isasii .
The name Austrocheirus ( gr. Austros - "southern"; cheirus - "hand") means something like "southern hand" and is intended to refer to the hand as a prominent feature of this genus. The specific epithet , isasii , honors Marcelo Isasi for his many years of work as a taxidermist of paleontological finds and for the discovery of the Austrocheirus fossil.
features
Austrocheirus was a medium-sized theropod with an estimated body length of 7 to 8 m. While derived representatives of the Abelisauridae , such as Majungasaurus , Aucasaurus and Carnotaurus , had proportionally very short, reduced arms, the arms of Austrocheirus were not regressed. This means that Austrocheirus is the only known medium-sized, Late Cretaceous Abelis auroid with non-shortened arms. The researchers conclude that the reduction of the arms in derived abelisaurids is not directly related to their larger body size, but that it is an apomorphism of this group.
The approximate age of the individual can be estimated using the bone structure of the third metacarpal bone. For example, the outermost cortex shows some very closely spaced lines of diminished growth - this feature known as the External Fundamental System indicates that it was an adult individual. However, since the cortex has not yet been completely remodeled by secondary osteons , it was probably not a very old individual.
This genus can be distinguished from other genera on the basis of a number of unique anatomical features: for example, the third metacarpal bone (metacarpale III) has a dorsoventrally narrowed shaft, while the toe bones (phalanges) have a longitudinal crest.
Systematics
Austrocheirus is a basal (original) representative of the Abelisauroidea , a group within the Ceratosauria . However, a phylogenetic analysis carried out by Ezcurra and colleagues (2010) cannot resolve the exact relationship to other basal Abelis auroid; in this analysis Austrocheirus forms a polytomy with the genera Noasaurus , Ligabueino , Masiakasaurus , Elaphrosaurus and the group Abelisauridae .
Find
The only find so far was discovered in March 2002 at the Hoyada Arroyo Seco site , near the west bank of the Río La Leona in southwest Santa Cruz . The find comes from the Pari-Aike formation (Lower Maastrichtian ). Other dinosaur finds in this formation include the basal ornithopod Talenkaue , the titanosaur Puertasaurus , and the basal Tetanurae Orkoraptor .
The find ( holotype , specimen number MPM-PV 10003) consists of incomplete caudal vertebrae, a left third metacarpal bone, a left finger bone of the third finger, the lower end of a shin bone (tibia) and the fragmentary left third metatarsal bone. The bones were found in an area of 2 m². Since the bones are of the same size and no further remains of terrestrial vertebrates have been found, all bones can be attributed to a single individual.
literature
- Martín D. Ezcurra, Federico L. Agnolin, Fernando E. Novas : An abelisauroid dinosaur with a non-atrophied manus from the Late Cretaceous Pari Aike Formation of southern Patagonia. In: Zootaxa . No. 2450, 2010, pp. 1-25.