Megaraptor

Megaraptor; Temporal range: Late Cretaceous (Turonian – Coniacian) 90–88 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
	Reconstructed skeleton in Japan
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
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, the type genus and namesake of the clade Megaraptora and family Megaraptoridae. Its fossils have been discovered in the Patagonian Portezuelo Formation of Argentina, South America, dating to the Turonian and Coniacian ages of the Late Cretaceous, roughly 90–88 million years ago. One species of Megaraptor, M. namunhuaiquii, has thus been named, known from four partial or fragmentary skeletons, with only one including a skull.

The type specimen of Megaraptor consists of a fragmentary assemblage of limb bones, discovered in 1996 by Argentine palaeontologist Fernando E. Novas. Believing that a large claw found at the site came from the animal's foot, he determined that it was probably a coelurosaur related to dromaeosaurs and troodontids, and named it accordingly. While Novas never stated that Megaraptor belonged to either family, contemporary depictions often portrayed it as a giant dromaeosaurid. The discovery of another specimen revealed that Megaraptor's large claw actually came from its hand, and it was surmised in 2004 to belong to a novel lineage predating the carnosaur–coelurosaur split. Subsequent analyses recovered Megaraptor and related genera (collectively known as megaraptorans) as relatives of the allosauroid Neovenator, though since the description of a relatively complete juvenile skull in 2014, it has been recovered primarily within Coelurosauria, and may have been a close relative of tyrannosaurs.

No complete skeletons of Megaraptor are known, so its anatomy has been pieced together over the years through only a few fragmentary specimens. It has been estimated that Megaraptor measured 8 m (26 ft) in length, and weighed around 1 t (2,200 lb). Its skull, the anatomy of which is known exclusively from a juvenile specimen, was long, low, and slender, though was likely deeper and more robust, with smaller eye sockets, in adults. Similar to tyrannosaurs, it had small, conical teeth at the front of its jaws, and longer, more curved teeth near the back, a condition known as heterodonty. Megaraptor had very large deltopectoral crests on its upper arm bones, and various other muscle attachment sites suggest that its arms were strong. The hand claws of Megaraptor were very long and strongly curved, with the claw of the first finger measuring 35 cm (14 in) in total length; the claw of the third finger was the smallest, only 6.5 cm (2.6 in) in length. Similar to dromaeosaurids and birds of prey, these claws may have been lengthened considerably by a sheath of keratin.

The depositional environment of the Portezuelo Formation was a fluvial (river) deposit, with a humid climate. Megaraptor would have shared its ecosystem with various other non-avian archosaurs, including the abelisaurid, Elemgasem, the titanosaurian sauropod, Futalogknosaurus, the unenlagiine theropod, Unenlagia, and the azhdarchoid pterosaur, Argentinadraco. It was initially suggested that Megaraptor may have used its hand claws to open carcasses, though a role in active predation is now generally favoured. Due to the relatively gracile construction of its skull compared to that of other theropods, Megaraptor, along with other megaraptorans such as Australovenator, may have relied on its large hand claws to grab prey items, pulling them towards its chest so that they could be dispatched by its jaws.

History of discovery

In January 1996,^[2] Argentine palaeontologist Fernando E. Novas recovered the fragmentary remains of a large theropod, consisting of a right ulna, a left manual phalanx (finger bone), part of a right metatarsal, and a very large ungual phalanx (claw). It was discovered in strata belonging to the Portezuelo Formation, part of the Río Neuquén Subgroup in Neuquén, northwestern Patagonia. The specimen, catalogued as MCF-PVPH 79, was transported to the Museo Carmen Funes, a palaeontological collection in Plaza Huincul.^[1] In December 1997, Novas presented a cast of the ungual, which he believed to come from the second digit of the foot, to the Houston Museum of National Sciences.^[2] The next year, he described it in a paper published in the Journal of Vertebrate Paleontology. Believing that the new taxon was related in some capacity to dromaeosaurids and troodontids, (though noting that a more basal position was possible), Novas gave it the binomial name Megaraptor namunhuaiquii. The genus name derives from the Greek mega (large) and the Latin raptor (thief), while the species name derives from the Mapuche namun (foot) and huaiqui (lance).^[1] Though Novas never expressed a belief that M. namunhuaiquii was a dromaeosaurid, it was nevertheless depicted as such in contemporary palaeoart.^[3] In 2004, a second Megaraptor specimen (MUCPv 341), was described in a paper helmed by Jorge O. Calvo. Consisting of a right ulna, radius and a complete manus (hand) found in association with a sauropod femur, it demonstrated that the large ungual belonged to the first digit of the manus, as opposed to the second digit of the foot, and led its describers to suggest a position predating the coelurosaur–allosauroid split.^[4] In 2014, a third M. namunhuaiquii specimen (MUCPv 595), consisting of the partial skeleton of a juvenile, was described by a team led by Juan D. Porfiri.^[5] A fourth specimen (MUCPv 278), consisting of a humerus, was described in 2025.^[6] Another specimen (MUCPv 1353) is known but has yet to be described.^[3]^[5]

Description

Size

South American megaraptorids were generally very large, exceeding 7 m (23 ft) in length and 1 t (1,000 kg) in mass.^[7] The holotype of Megaraptor was estimated by Fernando Novas to measure around 8 m (26 ft) in length.^[1] In 2010, Gregory S. Paul estimated its length at 8 m (26 ft), its weight at 1 t (2,200 lb).^[8] Porfiri et al., in their 2014 paper describing MUCPv 595, estimated the length of a mature specimen at 9–10 m (30–33 ft) based on the proportions of Allosaurus.^[5] In 2016, extrapolating instead from other megaraptorans, Asier Larramendi and Rubén Molina-Pérez estimated that Megaraptor had a body length of 8.3 m (27 ft), a hip height of 2.35 m (7.7 ft), and a body mass of 1.3 t (2,900 lb).^[9] MUCPv 595 has an estimated body length of 3 m (9.8 ft).^[5]^[6] While MUCPv 278 is known only from a humerus, that humerus, is roughly twice the size of the equivalent bone in the juvenile specimen, and one-third larger than that of Australovenator.^[6]

Skull

The skull of Megaraptor is known from a single juvenile specimen, MUCPv 595, which preserves both premaxillae and maxillae, nasals, a left frontal, and a partial braincase.^[5] It was fairly gracile and weak compared to that of other theropods, possibly a consequence of the development of more powerful and mobile forelimbs and thus a decreased reliance on the skull for predation.^[3] The premaxilla is fairly small and bears several large foramina, as in many tyrannosauroids. The maxilla is long and subtriangular, and has a combination of coelurosaur traits, such as the lengthening of the anterior (front) maxillary ramus, and allosauroid traits, such as the straightness of the dorsal (upper) margin. At the same time, there are traits that match neither group, such as the overall morphology of the maxillary ramus. The nasals were paired and unfused, though this may be attributed to the juvenile nature of the known skull. Similarly, the nasal rugosities present in many other basal tetanurans are absent, though this may again be due to the specimen's age upon death. The frontal is quadrangular, with a wide supratemporal fossa, bound by a strong ridge which contacted that of the opposite frontal, very similar to the condition seen in tyrannosauroids and unlike that of allosauroids. The braincase, too, has a mosaic of coelurosaur (particularly tyrannosauroid) and allosauroid traits. At least four teeth were present in each premaxilla, and presumably fifteen were present in each maxilla. Megaraptor's teeth were heterodont, meaning that two different tooth shapes were present: the premaxillary teeth were short and conical, whereas the maxillary teeth were larger and more recurved. This resembles the pattern seen in tyrannosauroids.^[5] Allesio Ciaffi et al., in 2025, used allometry to determine that the skull of a fully mature Megaraptor would likely have been deeper and more robust than that of MUCPv 595, and that the orbits (eye sockets) would have proportionally been smaller. They did, however, note the caveat that much of Megaraptor's postcranial skeleton (the elements posterior to the skull, or behind it) contradicts what might be assumed based on allometry alone, and that the same may apply to cranial elements.^[3]

Postcranial skeleton

Megaraptor's neck contained ten cervical vertebrae. The neural spine of the axis (the second cervical vertebra) was tall and narrow, with a convex dorsal margin, resembling basal coelurosaurs like Scipionyx, while differing from allosauroids and derived tyrannosauroids. All of the cervical vertebrae were opisthocoelous, meaning that they were convex anteriorly and concave posteriorly (towards the back).^[5] The torso of Megaraptor was fairly wide and deep,^[3] and contained twelve dorsal vertebrae. The first four neural spines were short dorsoventrally (top-to-bottom) and anteroposteriorly (front-to-back), while those further along the vertebral column were longer and taller. Eight gastralia, bones which support the abdominal organs and serve as muscle attachment points, are known. They resemble those of carcharodontosaurids and tyrannosaurids, while differing from those of most non-tyrannosaur coelurosaurs. The exception is Sinocalliopteryx, which has very similar gastralia. The gastralia were large, being slightly shorter than the dorsal ribs, similar to the condition seen in other large theropods. The sacrum, a mass of fused vertebrae which sat at the hips, contained five vertebrae.^[5] Only two caudal (tail) vertebrae are known from Megaraptor, both possessing blade-like neural spines as deep as those of Allosaurus.^[4]

The pectoral girdle of Megaraptor differed from that of carcharodontosaurids in that its scapula was slenderer, and the acromial process was shallower, though resembled that of Allosaurus. The coracoid was almost flat,^[4] and had a slightly developed biceps tuber. Characteristic of megaraptorans, there was a deep depression behind the glenoid.^[5] Though Megaraptor's humeri (upper arm bones) are poorly known, megaraptorans overall had large, robust deltopectoral crests. Megaraptorans as a whole had attachment sites for strong forelimb flexor and extensor muscles.^[10] Megaraptor's forearm, measured from the proximal (close to the body) end of the radius to the distal (far from the body) end of the first digit, measured 93.8 cm (36.9 in), with the manus alone comprising around 70 cm (28 in) of that.^[4] Though fragmentary, the carpals of Megaraptor are known to have been semi-lunate (crescent-shaped), similar to the related Australovenator and to certain coelurosaurs.^[11] The hands were unusually elongate.^[12] The first ungual (claw) was very large, and, if measured along its curve, was around 35 cm (14 in) in length. The second ungual was smaller 23.5 cm (9.3 in), while the third was the smallest 6.5 cm (2.6 in).^[4] Each of Megaraptor's unguals was strongly curved, more so than in spinosaurids.^[12] In life, they would have been considerably lengthened by a keratin sheath, possibly to a similar extent as the pedal (foot) claws of dromaeosaurids and modern birds of prey.^[3] Due to their anatomy, and perceived similarities with the carcharodontosaurid Mapusaurus roseae, Juan D. Porfiri, Domenica Dos Santos, and Jorge O. Calvo suggested in 2007 that Megaraptor primarily used its forelimbs to open up carcasses, with the head serving as its primary weapon.^[13] However, this interpretation predates the discovery of MUCPv 595 and the elucidation of Megaraptor's skull morphology,^[3] and in 2023, Aranciaga Ronaldo et al. indicated that they had a more conventional role in prey capture.^[10] The related Australovenator had very mobile forelimbs and wrists, possibly adapted to grip onto prey items and draw them towards the chest so that they could be dispatched via the jaws,^[14] and the same may have been true of megaraptorans overall, including Megaraptor itself.^[3]^[14]

Classification

In his paper describing Megaraptor, Fernando Novas expressed uncertainty about its taxonomic position. While he tentatively placed it within Coelurosauria, and named it based on perceived similarities to dromaeosaurids and troodontids, he noted similarities to more basal theropod clades.^[1] In their reappraisal of the genus, Calvo et al. discounted the hypothesis that it was a coelurosaur, and suggested that it was instead a basal tetanuran, belonging to a clade that predated the split between allosauroids and coelurosaurs.^[4] Roger B. J. Benson, Matthew T. Carrano and Stephen L. Brusatte erected the clade Megaraptora to encompass Megaraptor and its closest relatives. Megaraptorans were placed within the family Neovenatoridae, and were therefore considered carcharodontosaurs.^[15] The 2014 paper describing a juvenile Megaraptor suggested, based on a phylogenetic analysis, that megaraptorans were nested within Tyrannosauroidea.^[5]

The cladogram shown below follows an analysis by Porfiri et al., 2014.^[5]

Megaraptora

Fukuiraptor

Megaraptoridae

	Australovenator

	Aerosteon

unnamed	Orkoraptor

	Eotyrannus

	Megaraptor

In their 2022 description of Maip macrothorax, 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).^[16]