Megaraptor Temporal range: Late Cretaceous, [1]
Reconstructed hand
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Clade:	†Megaraptora
Family:	†Megaraptoridae
Genus:	†Megaraptor Novas 1998
Species:	†M. namunhuaiquii
Binomial name
†Megaraptor namunhuaiquii Novas 1998

Megaraptor (lit. 'large thief') is a genus of large theropod dinosaur that lived in the ages of the Late Cretaceous.^[2][3] 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.^[4][5]

Description

Claw cast with a ruler for scale

Size of two specimens compared to a human

Megaraptor head reconstruction based on the juvenile skull

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.^[2] The discovery of a fully preserved front limb, however, showed that this giant, razor claw actually came from the first digit of the animal's hand. In 2010, Gregory S. Paul estimated its length at 8 metres (26 ft), its weight at 1 tonne (2,200 lb).^[6] The hands were unusually elongated, bearing sickle-shaped claws even more recurved than those of spinosaurids.^[7]

Classification

The hand is quite distinct from other basal tetanurans, so it was not initially clear whether Megaraptor was an allosaurid, a carcharodontosaurid, a spinosauroid, or something else entirely.^[3] 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.^[8] More recent studies have proposed that Megaraptor and its kin are actually tyrannosauroids^[9] or spinosauroids^[10] as opposed to allosauroids.^[9] A juvenile specimen described in 2014 has provided more evidence towards Megaraptor being a primitive tyrannosauroid.^[11] The discovery of Gualicho indicates that Megaraptor may not be a tyrannosauroid, but either an allosauroid or basal coelurosaur.^[12]

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.^[1]

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).^[13]

Megaraptora	Phuwiangvenator Vayuraptor Fukuiraptor Megaraptoridae Australian megaraptorid indet. (LRF 100–106) Australovenator "Clade A" Aoniraptor Bajo Barreal Formation megaraptorid indet. (UNPSJB-Pv 944/958) Megaraptor Murusraptor "Clade B" Orkoraptor Tratayenia Maip Aerosteon

Paleoecology

Hypothetical life restoration of an adult

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.^[14] 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