| Buitreraptor | |
|---|---|
 | |
| Mounted skeleton,Royal Ontario Museum, Toronto, Canada | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Dromaeosauridae |
| Subfamily: | †Unenlagiinae |
| Genus: | †Buitreraptor Makovickyet al.2005 |
| Type species | |
| †Buitreraptor gonzalezorum Makovickyet al. 2005 | |
Buitreraptor (meaning "La Buitrera seizer") is a genus ofdromaeosauriddinosaurs that lived during theLate Cretaceous ofArgentina at theCandeleros Formation.Buitreraptor was described in 2005 and thetype species isBuitreraptor gonzalezorum. It was rooster-sized and had a very elongated head with many small teeth.
Four specimens ofBuitreraptor were found in 2004 insandstone inPatagonia,Argentina during an excavation led bySebastián Apesteguia, researcher of CONICET at theFundacion Felix de Azara - Maimonides University, andPeter Makovicky, curator of dinosaurs at theField Museum in Chicago.Buitreraptor is from the earlyLate CretaceousCandeleros Formation, dating to theCenomanian-Turonian ages approximately 98 to 97 million years ago, whenSouth America was an isolated continent likeAustralia today. It was uncovered in a famous fossil site namedLa Buitrera, the "vulture roost". Although dinosaurs are rare in this site, another nearby site had earlier yielded the giantGiganotosaurus, one of the largest known carnivorous dinosaurs.[1]
Buitreraptor gonzalezorum is the only known species of thegenusBuitreraptor. It was named by Peter Makovicky, Sebastián Apesteguía andFederico Agnolín. The genus name means "vulture raider", from the Spanish wordbuitre meaningvulture, in reference toLa Buitrera, andLatinraptor, "seizer". Thespecific name honours the González brothers, Fábian and Jorge, who realised much of the actual excavation and preparation of the fossils.[1] Theholotype specimen,MPCA 245, consists of a partial skeleton with skull of an adult individual. Theparatype is MPCA 238, a sacrum with a right pelvis and right hindlimb.[1] The skull of the holotype was described in detail in 2017,[2] while 2018 saw a slew of new papers on the anatomy of the genus. These include descriptions of new specimens,[3] a study on the tail anatomy of the genus,[4] and a general overview of thepostcrania of multiple specimens.[5]
Buitreraptor was a rather small dinosaur. In 2010,Gregory S. Paul estimated the length at 1.5 metres, the weight at three kilograms.[6]Buitreraptor has some different physical features than typical northern dromaeosaurs, such asVelociraptor.Buitreraptor has a slender, flat, extremely elongated snout with many small teeth that lack meat-tearing serrations or cutting edges and are grooved, strongly recurved and flattened.[7][8] From this, the scientists who initially described it concluded that this dinosaur was not a hunter of relatively large animals like some other dromaeosaurs, but rather a hunter of small animals such aslizards andmammals. The forelimbs ofBuitreraptor were long and ended in very long and thin three-fingered hands. All known parts of the hand ofBuitreraptor are proportionally longer than in the dromaeosauridsDeinonychus andVelociraptor, except for the ungual bones which are proportionally smaller inBuitreraptor.[3]
The body as a whole was also elongated, with a shallow ribcage. The enlarged sickle claw at the second toe of the foot formed a blade that was long although less large than in dromaeosaurids such asVelociraptor andDeinonychus.[3] No fossil discoveries have been made of any feathers ofBuitreraptor. However, there are relatives likeMicroraptor andSinornithosaurus, of which fossils with preserved feathers are known. Since its close relatives had feathers, it is likely thatBuitreraptor also was feathered. According to Apesteguia, this is comparable to reconstructing an extinctmonkey withfur because all modern monkeys have fur.[9]
Buitreraptor shows a mosaic of dromaeosaurid,troodontid andavialan traits. It was in 2005 assigned to theDromaeosauridae. Acladistic analysis by the describers showed it was part of the dromaeosauridUnenlagiinae.[1] The discovery ofBuitreraptor has also been the subject of discussion among scientists as to the question whether flight could have evolved independently in birds and dromaeosaurids or was derived from some flying common ancestor. Some scientists propose thatRahonavis, a relative toBuitreraptor, could fly. However, evidence for flight has not been unequivocally found in other dromaeosaurids, which has led some scientists to propose that dromaeosaurids evolved flight independently of birds ifRahonavis could indeed fly.[10]
The followingcladogram is based on the phylogenetic analysis conducted by Hartman and colleagues in 2019, showing the relationships ofBuitreraptor among the other genera assigned to the family "Unenlagiidae":[11]
Other thanBuitreraptor, the only other known dromaeosaurs from the southern continents areNeuquenraptor,Austroraptor, andUnenlagia from South America (discovered earlier in 2005),Rahonavis (once thought to be a true avian bird) fromMadagascar, and unidentified dromaeosaur-like teeth from Australia. This discovery in the Southern Hemisphere helped scientists to clarify that the dromaeosaur family was more widely dispersed around the world than previously thought. Evidence indicates that dromaeosaurs first appeared during theJurassic Period, when all the continents were much closer together than they are today. With the discovery ofBuitreraptor, the scientists proposed that dromaeosaurids originated somewhere around 180 million years ago, beforePangaea broke up.[1][12] However, other paleontologists have in later studies placed the time of origin for Dromaeosauridae to about 160 million years ago.[13]
The scientists see it as an alternative possibility that dromaeosaurids originated on the ancient continentLaurasia in the north and during the Cretaceous Period migrated to southernGondwana, since the species known from the Southern Hemisphere bear distinctive characteristics not shared by their northern relatives. La Buitrera also yielded remains of terrestrial crocodiles, pterosaurs, the largest knownrhynchocephalians, limbed snakes,iguanian lizards,chelid turtles, mammals, anddipnoan fishes[1]
Unenlagiines had better capacities for running and pursuit predation than other dromaeosaurids such asLaurasian dromaeosaurids (Eudromaeosauria), which were more stocky and had shorter legs and had an active predatory lifestyle. Unenlagiines were highlycursorial animals because they were more gracile and had modified metatarsals that are relatively thin and lengthened.[14] Based on these adaptations, it is likely that unenlagiines preyed on small, fast animals, although the exact animals are unknown.[8][15][16]Buitreraptor features particular traits that can be attributed to specific hunting methods. Models forBuitreraptor propose that it hunted bytraveling large distances in pursuit of prey, which may explain the long-legged trait shared by various genera of Unenlagiidae.Buitreraptor is characterized by its long forelimbs and hands; it likely relied on them to restrain prey and the curved claw of the second pedal digit would have injured or killed the victim.Buitreraptor probably swallowed its prey whole due to its lack of serrated teeth with flesh-tearing capabilities; the teeth functioned to simply hold prey.[17]
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