Rahonavis Ostromi

''Rahonavis'' is a genus of bird-like theropods from the Late Cretaceous ( Maastrichtian, about 70 mya) of what is now northwestern Madagascar. It is known from a partial skeleton ( UA 8656) found by Catherine Forster and colleagues in Maevarano Formation rocks at a quarry near Berivotra, Mahajanga Province.Tudge, Colin (2009) ''The Bird:A Natural History of Who Birds Are, Where They Came From, and How They Live'

/ref> ''Rahonavis'' was a small predator, at about long and 0.45-2.27 kg (1-5 lbs),Holtz, Thomas R. Jr. (2008) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages'
Supplementary Information
/ref> with the typical ''Velociraptor''-like raised sickle claw on the second toe. It was originally the first African coelurosaur until the Nqwebasaurus was discovered in 2000.

The name ''Rahonavis'' means, approximately, "cloud menace bird", from Malagasy ' (RA-hoo-na, "cloud" or "menace") + Latin ' "bird". The specific name, ''R. ostromi'', was coined in honor of John Ostrom.

Discovery and species

The fossilized remains of ''Rahonavis'' were first recovered from the Maevarano Formation in Madagascar in 1995 by a joint expedition of SUNY and the University of Antananarivo, near the village of Berivotra. 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 giant titanosaur were revealed. It was during the excavation of this find that paleontologists discovered the bones of ''Rahonavis'' 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 related ''Archaeopteryx'', about the size of a modern raven.

The lack of well-documented relatives of this species nonwithstanding, a single thoracic vertebra ( NMC 50852) most similar to those of ''R. ostromi'' was found in the Albian to Cenomanian Kem Kem Beds Lagerstätte in Morocco. Lacking the pleurocoels found in ''Rahonavis'' and having a larger neural canal, it appears to belong to a different genus. Although former character can vary in species of the same genus, in individual vertebrae of the same animal, and ontogenetically, the distance in space and time suggests that whatever this specimen may be, it does not belong into ''Rahonavis''.

A dentary has been found in association with the holotype, though it is seldom described.

Classification

''Rahonavis'' has historically been the subject of some uncertainty as to its proper taxonomic position – whether it is a member of the clade Avialae (birds) or a closely related dromaeosaurid. The presence of quill knobs on its ulna (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 place ''Rahonavis'' firmly among or outside the birds.

''Rahonavis'' could be a close relative to ''Archaeopteryx'', as originally suggested by the describers, and thus a member of the clade Avialae, but while the pelvis shows adaptations to flight similar in function to those of ''Archaeopteryx'', they seem to be independently derived.

Beginning in the early 2000s, a consensus emerged among most theropod researchers that ''Rahonavis'' was more closely related to deinonychosaurs than to avialans, and specifically was a member of the South American dromaeosaurid clade Unenlagiinae. A 2005 analysis by Makovicky and colleagues found ''Rahonavis'' to be closely related to the unenlagiines '' Unenlagia'' and '' Buitreraptor''.Supplementary information
Norell and colleagues (2006) also found ''Rahonavis'' to lie within the Unenlagiinae, as the sister taxon to ''Unenlagia'' itself. A 2007 study by Turner and colleagues again found it to be an unenlagiine dromaeosaurid, closely related to ''Unenlagia''.

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 to dromaeosaurines. A large analysis published by Agnolín and Novas (2013) recovered ''Rahonavis'' as closer to Avialae than to Dromaeosauridae. A cladistic analysis by Cau (2018) recovered ''Rahonavis'' as a probable relative of the long-tailed Early Cretaceous avialans '' Jeholornis'' and ''Jixiangornis''. The analysis of Hartman ''et al''. (2019) "strongly rejected" the supposed avialan position of ''Rahonavis'', finding its placement in Unenlagiinae better supported as it takes 10 less steps. In 2020, ''Rahonavis'' and the South American '' Overoraptor'' were found to be sister taxa in a clade sister to the Avialae.

The discoverers of ''Rahonavis'' initially named it ''Rahona'' but changed the name after discovering that the name '' Rahona'' was already assigned to a genus of lymantriid moths.

Paleobiology

Although numerous artists' reconstructions of ''Rahonavis'' 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 that ''Rahonavis'' represents a chimera consisting of the forelimb of a bird conflated with the skeleton of a dromaeosaurid, and consider ''Rahona'' as described a ''nomen dubium''. The nearby discovery of the primitive bird ''Vorona berivotrensis'' at least shows that the possibility of a mix-up cannot be fully excluded. However, many other scientists, including the original describers of ''Rahonavis'', 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 to ''Rahonavis'' were buried in an area "smaller than a letter-sized page", according to co-describer Luis M. Chiappe in his 2007 book ''Glorified 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.

Chiappe maintained that ''Rahonavis'' could probably fly, noting that its ulna was large and robust compared to ''Archaeopteryx'', and that this fact, coupled with the prominent quill knobs, suggest that ''Rahonavis'' 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 that ''Rahonavis'' was capable of flight, though it would have been more "clumsy in the air than modern birds." Agnolín and Novas (2013) noted that, like '' Microraptor'', a bat-like flightstroke using the deltoideus complexes seems to have been likely in ''R. ostromi''.

See also

* Timeline of dromaeosaurid research

References

Further reading

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{{Taxonbar, from=Q131167

Unenlagiines
Feathered dinosaurs
Late Cretaceous birds
Maastrichtian genus first appearances
Maastrichtian life
Maastrichtian genus extinctions
Dinosaurs of India and Madagascar
Cretaceous Madagascar
Fossils of Madagascar
Maevarano fauna
Late Cretaceous animals of Africa
Cretaceous Morocco
Fossils of Morocco
Fossil taxa described in 1998
Taxa named by Catherine Forster
Taxa named by Scott D. Sampson
Taxa named by Luis M. Chiappe