Noasaurus

Noasaurus ("Northwestern Argentina lizard") is a genus of ceratosaurian theropod dinosaur from the Maastrichtian (Late Cretaceous) of Argentina. The type and only species is N. leali. The fragmentary holotype specimen of Noasaurus, PVL 4061, consisting of a few cranial and postcranial bones, was discovered from strata from the Lecho Formation of Southern Salta in 1975 by a team led by José Fernando Bonaparte. When described by Bonaparte and in PhD student Jaime Powell in 1980, it was believed to be a coelurosaur theropod and assigned to a family of its own; this family, Noasauridae, still exists, though has been reassigned to Ceratosauria. Noasaurus was a fairly small theropod, with PVL 4061 measuring somewhere between in length. Initially, it was believed that two strongly curved unguals (claws) found alongside the holotype were evidence of raptorial foot claws, like those of dromaeosaurids. However, it is now known that they belonged to Noasaurus ' forelimbs, and were thus functionally similar to those of spinosaurids. Therefore, rather than converging on dromaeosaurids, it may have been an opportunistic mesopredator, feeding on small vertebrates, including fish.

Noasaurus ("Northwestern Argentina lizard") is a genus of ceratosaurian theropod dinosaur from the Maastrichtian (Late Cretaceous) of Argentina. The type and only species is N. leali. The fragmentary holotype specimen of Noasaurus, PVL 4061, consisting of a few cranial and postcranial bones, was discovered from strata from the Lecho Formation of Southern Salta in 1975 by a team led by José Fernando Bonaparte. When described by Bonaparte and in PhD student Jaime Powell in 1980, it was believed to be a coelurosaur theropod and assigned to a family of its own; this family, Noasauridae, still exists, though has been reassigned to Ceratosauria. Noasaurus was a fairly small theropod, with PVL 4061 measuring somewhere between in length. Initially, it was believed that two strongly curved unguals (claws) found alongside the holotype were evidence of raptorial foot claws, like those of dromaeosaurids. However, it is now known that they belonged to Noasaurus ' forelimbs, and were thus functionally similar to those of spinosaurids. Therefore, rather than converging on dromaeosaurids, it may have been an opportunistic mesopredator, feeding on small vertebrates, including fish. ==Discovery and naming== During the latter half of the 20th century, a series of fossil-hunting expeditions were dispatched across to Argentina. In April 1975, an team of college students and paleontologists from the of San Miguel de Tucumán explored fossiliferous outcrops at El Brete, south of the El Brete Estancia, which is a fossiliferous (fossil-bearing) site that is from the middle section of the Lecho Formation. These layers derive from the Maastrichtian stage of the Late Cretaceous Period, dating to between 70 million and 68 million years old. Led by Argentine paleontologist Jose Bonaparte, the group unearthed a bonebed of disarticulated dinosaur fossils, numbering over 100 bones, from several different dinosaur taxa. These fossils were excavated from May to August 1975, though fieldwork at the site continued over the next two years. A disarticulated partial skeleton of a theropod dinosaur was discovered in 1975 or 76 by Jaime Eduardo Powell, a PhD student of Bonaparte's, among a skeleton of the titanosaur Saltasaurus. These fossils were transported to the in San Miguel de Tucumán where they was prepared and cataloged. The skeleton, cataloged under PVL 4061, contains the maxilla, the quadrate bone, two cervical (neck) vertebrae, two cervical ribs, the centrum of a back vertebra, two hand claws, a finger phalanx and the second right metatarsal bone. One of the hand claws was initially identified as a second toe claw. In 2004, it was recognised as a hand claw, at which occasion the second hand claw was referred. The tetrapod fossils of El Brete were first recorded by Boneparte et al. in 1977, including the theropod recovered which was described as belonging to a coelurosaur theropod. The type and only known species, Noasaurus leali, was named and briefly described by Bonaparte and Powell in 1980 alongside Saltasaurus. The generic name Noasaurus begins with a usual abbreviation of noroeste Argentina, "northwest Argentina". The specific name honours the discoverer of the site, Juan Carlos Leal. The unusual nature of Noasaurus ' anatomy led Bonaparte to erect the family Noasauridae, a group originally thought to be closely related to the basal coelurosaurians Coelurus and Compsognathus. Noasaurus remained poorly described and enigmatic for many years, with it only getting its brief description in 1980 and little further research, whereas its contemporary Saltasaurus and enantiornithines received full descriptions. In 1999, a cervical (neck) vertebra found at the site, specimen MACN 622, was identified as oviraptorosaurian, a rare proof that the Oviraptorosauria had invaded the Gondwanan continents. In 2007 however, it was reidentified as a noasaurid vertebra, probably belonging to the Noasaurus holotype. The decades following Noasaurus ' description revealed that it was one of many noasaurid dinosaurs in the group Ceratosauria, with genera named from Madagascar, Brazil, and many other countries. In 2024, a study by an international team of researchers led by Christophe Hendrickx described the holotype of Noasaurus in further detail and evaluated its paleobiology, paleoecology, classification, and anatomy. ==Description== Noasaurus was a small theropod. Gregory S. Paul estimated its length at and its weight at . In 2024, Hendrickx et al. used the reconstructed size of the skull and the dimensions of the second metatarsal to provide length estimates of and , respectively. They abstained from providing a mass estimate due to the lack of the necessary limb elements, and the possibility that the Noasaurus holotype was a juvenile. A histological analysis could not be performed on the holotype, as it was prohibited, thus its age is currently unknown. ==Classification== Noasaurus is today considered to be a member of the Ceratosauria. Originally, it was seen as a member of the Coelurosauria. Bonaparte and Powell assigned it to a family of its own, the Noasauridae. In 1988, Gregory S. Paul subsumed Noasauridae into Abelisauridae as a subfamily. He believed abelisaurids to be representatives of Megalosauria, and indicated in a cladogram that they may might have evolved from a sister to Megalosaurus. While subsequent analyses have consistently recovered noasaurids as close relatives of abelisaurids, starting with a 1991 paper by José Bonaparte, they now form a clade of their own, Abelisauroidea, within Ceratosauria. The following cladogram is based on the phylogenetic analysis conducted by Rauhut and Carrano in 2016, showing the relationships of Elaphrosaurus among the noasaurids: In 2024, Hendrickx et al.. recovered Noasaurus in a polytomy with Laevisuchus, Masiakasaurus, Velocisaurus, and Vespersaurus, likely representing a radiation of small-bodied noasaurids that occurred during the Late Cretaceous. ==Paleobiology== In 1980, it was thought that the presumed foot claw functioned as a sickle claw. Paul in 1988 saw the noasaurines as the South-American counterparts of the Asian and North-American dromaeosaurids, in a process of convergent evolution. Noting that abelisaurids tend to have very short arms, he wondered whether the forelimbs of Noasaurus were of limited length also, forcing the animal to employ a kicking technique instead of grasping the back of a victim in order to disembowel it with the foot claws, a method he assumed the dromaeosaurids used. This hypothesis was undermined when it was determined that the foot claw was in fact a hand claw. Instead, as proposed by Hendrickx et al.. in 2024, it may have been utilised to snag fish from the water, making it instead convergent with the enlarged thumb claw of spinosaurids like Baryonyx. They concluded that it was likely an opportunistic mesopredator that fed on small vertebrates, such as fishes. This lifestyle is similar to that proposed for Masiakasaurus. ==See also== Timeline of ceratosaur research ==References== ==Sources==

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