Megaraptor

''Megaraptor'' () is a genus of large theropod dinosaur that lived in the ages of the Late Cretaceous. Its fossils have been discovered in the Patagonian Portezuelo Formation of Argentina, South America. Initially thought to have been a giant dromaeosaur-like coelurosaur, it was classified as a neovenatorid allosauroid in previous phylogenies, but more recent phylogeny and discoveries of related megaraptoran genera has placed it as either a basal tyrannosauroid or a basal coelurosaur with some studies still considering it a neovenatorid.

Description

''Megaraptor'' was initially described as a giant dromaeosaur, known primarily from a single claw (about 30 cm long) that resembled the sickle-shaped foot claw of dromaeosaurids. The discovery of a complete front limb, however, showed that this giant claw actually came from the first finger of the hand. In 2010, Gregory S. Paul estimated its length at , its weight at . The hands were unusually elongated, bearing sickle-shaped claws even more recurved than those of spinosaurids.Calvo, J.O., Porfiri, J.D., González-Riga, B.J., and Kellner, A.W. (2007) "A new Cretaceous terrestrial ecosystem from Gondwana with the description of a new sauropod dinosaur". ''Anais da Academia Brasileira de Ciências'', 79(3): 529–4

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Classification

The hand is quite distinct from other basal Tetanurae, tetanurans, so it was not initially clear whether ''Megaraptor'' was an allosaurid, a carcharodontosaurid, a spinosauroid, or something else entirely. Subsequent studies, as well as the identification of close relatives with similar large claws on the forelimbs (see below), helped identify ''Megaraptor'' as a highly advanced and lightly built allosauroid, and a member of the family Neovenatoridae. More recent studies have proposed that ''Megaraptor'' and its kin are actually tyrannosauroids or spinosauroids as opposed to allosauroids. A juvenile specimen described in 2014 has provided more evidence towards ''Megaraptor'' being a primitive tyrannosauroid. The discovery of ''Gualicho'' indicates that ''Megaraptor'' may not be a tyrannosauroid, but either an allosauroid or basal coelurosaur.

When first discovered and prior to publication, the spinosaurid ''Baryonyx'' was also reported to be a dromaeosaurid, and the allosauroid ''Chilantaisaurus'' was reported to be a possible spinosaurid, both based on the large hand claws.

The cladogram shown below follows an analysis by Porfiri ''et al.'', 2014.

In the 2022 description of '' Maip'', Rolando ''et al.'' noted the presence of two distinct megaraptoran clades: a more inclusive clade, comprising all megaraptorids except '' Fukuiraptor'' and ''Australovenator'', (shown below as "Clade A"), and a more exclusive clade of larger, entirely South American megaraptorids (shown below as "Clade B"). Like some previous analyses by other authors, Megaraptora is nested within Coelurosauria, as the sister taxon to Tyrannosauroidea. The cladogram below displays the megaraptoran results of the phylogenetic analyses by Rolando ''et al'' (2022).

Paleoecology

''Megaraptor'' is known from the Late Turonian to Early Coniacian-dated Portezuelo Formation of Argentina. Other named dinosaurs known from the formation include the titanosaurian sauropods ''Futalognkosaurus'', '' Baalsaurus'', and ''Malarguesaurus'', and several other theropod taxa including the dromaeosaurids '' Neuquenraptor'', ''Unenlagia'', and '' Pamparaptor'', the alvarezsaurid '' Patagonykus'', and the abelisaurid '' Elemgasem''. Indeterminate remains belonging to an unnamed megaraptorid, a possible noasaurid, and ornithopods have also been recovered from the formation. Fossils of teleost fish (''Leufuichthys''), turtles ('' Portezueloemys'' and a species of ''Prochelidella''), birds, and pterosaurs ('' Argentinadraco'') are also known.

References

External links

Science Daily

{{Portal bar, Dinosaurs, Paleontology, Cretaceous

Megaraptorans
Coniacian life
Turonian life
Late Cretaceous dinosaurs of South America
Cretaceous Argentina
Fossils of Argentina
Portezuelo Formation
Fossil taxa described in 1998
Taxa named by Fernando Novas