| Rahonavis | |
|---|---|
 | |
| Reconstructed skeleton,Royal Ontario Museum | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | Paraves |
| Genus: | †Rahonavis Forsteret al., 1998b |
| Type species | |
| †Rahonavis ostromi | |
| Synonyms | |
| |
Rahonavis is agenus ofbird-liketheropod from theLate Cretaceous (Maastrichtian, from about 72.1 to 66mya) of what is now northwesternMadagascar. It is known from a partial skeleton (UA 8656) found byCatherine Forster and colleagues inMaevarano Formation rocks at a quarry nearBerivotra,Mahajanga Province.[1]Rahonavis was a small predator, at about 70 centimetres (2.3 ft) long and 0.45-2.27 kg (1-5 lbs),[2] with the typicaldromaesaurid-like raised sickle claw on the second toe. It was originally the first African coelurosaur until the discovery ofNqwebasaurus in 2000.[3]
The nameRahonavis means, approximately, "cloud menace bird", fromMalagasyrahona (RA-hoo-na, "cloud" or "menace") +Latinavis "bird". The specific name,R. ostromi, was coined in honor ofJohn Ostrom.
Thefossilized remains ofRahonavis were first recovered from theMaevarano Formation in Madagascar in 1995 by a joint expedition ofSUNY and theUniversity of Antananarivo, near the village ofBerivotra. Most geological formations in this area are covered in dense grass, making identification of fossils difficult. However, when a portion of hillside was exposed by fire, the remains of a gianttitanosaur were revealed. It was during the excavation of this find that paleontologists discovered the bones ofRahonavis among the bones of the much larger dinosaur.Rahonavis is known from this single specimen, consisting of the hind limbs, trunk, portions of the tail (all of which were found articulated), as well as portions of the wing and shoulder bones.Rahonavis was one-fifth larger than the closely relatedArchaeopteryx, about the size of a modernraven.[4]
The discoverers ofRahonavis initially named itRahona but changed the name after discovering that the nameRahona was already assigned to a genus oflymantriidmoths.[5][6]
The lack of well-documented relatives of this species notwithstanding, a singlethoracic vertebra (NMC 50852) most similar to those ofR. ostromi was found in theAlbian toCenomanianKem Kem Beds inMorocco. Lacking thepleurocoels found inRahonavis and having a largerneural canal, it appears to belong to a differentgenus. Although former character can vary in species of the same genus, in individual vertebrae of the same animal, andontogenetically, the distance in space and time suggests that whatever this specimen may be, it does not belong intoRahonavis.[7]
A dentary has been found in association with the holotype, though it is seldom described.[8]
Rahonavis has historically been the subject of some uncertainty as to its proper taxonomic position – whether it is a member of thecladeAvialae (birds) or a closely relateddromaeosaurid. The presence ofquill knobs on itsulna (forearm bone) led initially to its inclusion as an avialan; however, the rest of the skeleton is rather typically dromaeosaurid in its attributes. Given the extremely close affinities between basal birds and their dromaeosaurid cousins, along with the possibility that flight may have developed and been lost multiple times among these groups, it has been difficult to placeRahonavis firmly among or outside the birds.
Rahonavis could be a close relative toArchaeopteryx, as originally suggested by the describers, and thus a member of the clade Avialae, but while thepelvis shows adaptations to flight similar in function to those ofArchaeopteryx, some fringe researchers have claimed that these may have been independently derived.[9]
Beginning in the early 2000s, a consensus emerged among most theropod researchers thatRahonavis was more closely related todeinonychosaurs than to avialans, and specifically was a member of the South American dromaeosaurid cladeUnenlagiinae. A 2005 analysis by Makovicky and colleagues foundRahonavis to be closely related to the unenlagiinesUnenlagia andBuitreraptor.[10] Norell and colleagues (2006) also foundRahonavis to lie within the Unenlagiinae, as the sister taxon toUnenlagia itself.[11] A 2007 study by Turner and colleagues again found it to be an unenlagiine dromaeosaurid, closely related toUnenlagia.[12]
This consensus has been challenged, however, by a few studies published since 2009 that have found many traditional "dromaeosaurids", including the unenlagiines, closer to Avialae than todromaeosaurines. A large analysis published by Agnolín and Novas (2013) recoveredRahonavis as closer toAvialae than toDromaeosauridae.[13] A cladistic analysis by Cau (2018) recoveredRahonavis as a probable relative of the long-tailed Early Cretaceous avialansJeholornis andJixiangornis.[14] The analysis of Hartmanet al. (2019) "strongly rejected" the supposed avialan position ofRahonavis, finding its placement in Unenlagiinae better supported as it takes 10 less steps. This placement suggestsRahonavis is one among multiple different paravian lineages that evolved flight independently.[15] In 2020,Rahonavis and the South AmericanOveroraptor were found to be sister taxa in a clade sister to the Avialae with a dataset based on that of the 2013 study.[16] As of 2020, it is undecided among paleontologists whether the paravianRahonavis is an unenlagiine, a dromaeosaurid, or an avialan.[8]
Although numerous artists' reconstructions ofRahonavis show it in flight, it is not clear that it could fly; there has even been some doubt that the forearm material, which includes the quill knobs, belongs with the rest of the skeleton. Some researchers have suggested thatRahonavis represents achimera consisting of the forelimb of a bird conflated with the skeleton of a dromaeosaurid, and considerRahona as described anomen dubium.[9] The nearby discovery of the primitive birdVorona berivotrensis at least shows that the possibility of a mix-up cannot be fully excluded. However, many other scientists, including the original describers ofRahonavis, maintain that its remains belong to a single animal, citing the close proximity of the wing bones to the rest of the skeleton. All the bones attributed toRahonavis were buried in an area "smaller than a letter-sized page", according to co-describerLuis M. Chiappe in his 2007 bookGlorified Dinosaurs. Additionally, Chiappe argued that suggestions of a chimera by paleornithologist Larry Martin were based on Martin's misinterpretation of the wing and shoulder bones as being more advanced than they really are.[4]
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Chiappe maintained thatRahonavis could probably fly, noting that its ulna was large and robust compared toArchaeopteryx, and that this fact, coupled with the prominent quill knobs, suggest thatRahonavis had larger and more powerful wings than that earlier bird. Additionally,Rahonavis shoulder bones show evidence of ligament attachments allowing the independent mobility needed for flapping flight. Chiappe concluded thatRahonavis was capable of flight, though it would have been more "clumsy in the air than modern birds."[4] Agnolín and Novas (2013) noted that, likeMicroraptor, abat-like flightstroke using thedeltoideus complexes seems to have been likely inR. ostromi.[13]
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