''Austrocheirus'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

, possibly a

neoceratosaurian Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with ''Ceratosaurus'' than with birds. The oldest known ceratosaur, ''Saltriovenator'', dates to the earliest ...

, which existed during the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

period. It was named and described by

Martin Ezcurra Martin may refer to: Places * Martin City (disambiguation) * Martin County (disambiguation) * Martin Township (disambiguation) Antarctica * Martin Peninsula, Marie Byrd Land * Port Martin, Adelie Land * Point Martin, South Orkney Islands Austra ...

Federico Agnolin Federico (; ) is a given name and surname. It is a form of Frederick, most commonly found in Spanish, Portuguese and Italian. People with the given name Federico Artists * Federico Ágreda, Venezuelan composer and DJ. * Federico Aguilar Alcuaz, ...

and

Fernando Novas Fernando Emilio Novas (born 1960) is an Argentine paleontologist working for the Comparative Anatomy Department of the Bernardino Rivadavia Natural Sciences Museum in Buenos Aires, Argentina.

in 2010. It contains the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...

''Austrocheirus isasii''. The generic name means "southern hand". The specific epithet honours discoverer and preparator Marcelo Pablo Isasi. The

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s were found on 17 March 2002 in the Pari Aike Formation, which was originally dated to the

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval ...

, around 71 to 66 million years ago, but was more recently dated to the Cenomanian, around 96.2 million years ago. However, this strata is now believed to date to the

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campani ...

. These fossils consist of a partial manus (hand), a

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...

, axial bones, and a foot bone. In 2016, its length was estimated to be . In 2012 Holtz estimated it at 6.5 meters (24 feet), while in 2016 Molina-Pérez & Larramendi gave a higher estimation at 9.3 meters (30.5 feet) in length and 1 tonne (1.1 short tons) in weight. A

cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...

analysis indicated ''Austrocheirus'' had a basal position in the

Abelisauroidea 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 ...

, but was more derived than ''

Ceratosaurus ''Ceratosaurus'' (from Greek κέρας/κέρατος, ' meaning "horn" and σαῦρος ' meaning "lizard") was a carnivorous theropod dinosaur in the Late Jurassic period ( Kimmeridgian to Tithonian). The genus was first described in 1 ...

'' and '' Berberosaurus''. This would make it the first known mid-sized abelisauroid which did not possess the reduced forelimbs seen in other members of that clade. The referral of ''Austrocheirus'' to Abelisauroidea was challenged by Oliver Rauhut (2012), who claimed that the putative abelisauroid synapomorphies used to justify this referral are actually also present in the skeletons of non-abelisauroid theropods. Thus, according to Rauhut ''Austrocheirus'' can be only classified as a theropod dinosaur of uncertain phylogenetic placement.

References

Ceratosaurs Late Cretaceous dinosaurs of South America Cenomanian life Cretaceous Argentina Fossils of Argentina Fossil taxa described in 2010 Taxa named by Fernando Novas {{Cretaceous-reptile-stub

See also

References