Megaraptor

In January 1996, 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 (a bone which supported a claw in life). The specimen 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. In December 1997, Novas presented a cast of the ungual, which he believed came from the second digit of the foot, to the Houston Museum of Natural Science. 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), 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. In 2005, a third M. namunhuaiquii specimen (MUCPv 595), consisting of the partial skeleton of a juvenile with uncertain affinities, was discovered. The assignment of this specimen to M. namunhuaiquii has since been called into question, including by Porfiri himself. A fifth specimen assigned to M. namunhuaiquii (MUCPv 1353) is known, discovered in 2008. Consisting of assorted skull material and "a large part" of the postcranial skeleton, it has been described only in a thesis authored by Porfiri. That same thesis references two additional specimens, MUCPv 412 and MUCPv 413, which consist of parts of the ulna and a manual phalanx (finger bone). ==Description==

Size South American megaraptorids were generally very large, exceeding in length and in mass. The holotype of Megaraptor was estimated by Fernando Novas to measure around in length. Porfiri and colleagues, in their 2014 paper describing MUCPv 595, estimated the length of a mature specimen at based on the proportions of Allosaurus. MUCPv 595 has an estimated body length of . The lower jaw of M. namunhuaiquii is represented only by a left dentary, belonging to specimen MUCPv 1353. It is mostly complete, though has been extensively eroded. It is extremely elongated compared to many other theropods, closely resembling that of Australovenator. The alveolar process, the part of the dentary in which tooth sockets articulate, is difficult to make out. The tooth at the very front of the alveolar row may have projected forward slightly, although this may be an artefact of the poor preservation of the dentary. Neurovascular foramina are present throughout the dentary, more so than in Australovenator. The overall foramina count is closer to that of Neovenator. The teeth were heterodont, meaning that two different tooth shapes were present: the premaxillary teeth were short and conical, M. namunhuaiquii'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 , with the manus alone comprising around of that. It retains a fourth metacarpal, albeit with no phalanges (finger bones) attached; The hands were unusually elongate. The first ungual (the bone supporting the claw) was very large, around in length when measured along its curve. The second ungual was smaller , while the third was the smallest . Each of M. namunhuaiquii's unguals was strongly curved, more so than in spinosaurids. 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. ==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. In 2012, Roger B. J. Benson, Matthew T. Carrano and Stephen L. Brusatte erected the clade Megaraptora to encompass M. namunhuaiquii and its closest relatives. Megaraptorans were placed within the family Neovenatoridae, and were therefore considered carcharodontosaurs, and the same result was recovered in several papers thereafter. The below cladogram shows the results of the phylogenetic analysis performed by Zanno & Makovicky (2013), in their paper describing Siats: whereas a 2022 analysis by Ronaldo and colleagues recovered megaraptorans as the sister clade to Tyrannosauroidea. }} == Palaeobiology ==

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 may have used its forelimbs to open up carcasses, with the head serving as its primary weapon. At the same time, though, they drew comparisons with Deinonychus and affirmed that it was likely an active hunter like that genus. This interpretation predated the discovery of MUCPv 595 and the elucidation of M. namunhuaiquii's skull morphology, and the same may have been true of megaraptorans overall, including M. namunhuaiquii itself. == Palaeoecology ==

Megaraptor is known from the Late Turonian to Early Coniacian-dated Portezuelo Formation of Argentina, Other dinosaurs known from the formation include the titanosaurian sauropods Futalognkosaurus, Baalsaurus, and Malarguesaurus, and several other theropod taxa including the dromaeosaurids Neuquenraptor, Pamparaptor, and Unenlagia, 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. Non-vertebrate fossils from the Portezuelo Formation include bivalves, invertebrate trace fossils referrable to Scoyenia, and leaf impressions from a some kind of dicotyledonous plant. == References ==