Rahonavis

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Rahonavis
Temporal range:
Ma
↓
Reconstructed skeleton, Royal Ontario Museum
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: Paraves
Genus: †Rahonavis
Forster et al., 1998b
Type species
†Rahonavis ostromi
(Forster et al., 1998a) Forster et al., 1998b
Synonyms
  • Rahona Forster et al. 1998 non Griveaud 1975
  • Rahona ostromi
     Forster et al. 1998a

Rahonavis is a

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.[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 typical dromaesaurid-like raised sickle claw on the second toe. It was originally the first African coelurosaur until the discovery of Nqwebasaurus in 2000.[citation needed
]

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

Discovery and species

holotype specimen

The

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.[3]

The discoverers of Rahonavis initially named it Rahona but changed the name after discovering that the name

lymantriid moths.[4][5]

The lack of well-documented relatives of this species nonwithstanding, a single

Kem Kem Beds 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.[6]

A dentary has been found in association with the holotype, though it is seldom described.[7]

Classification

Size compared to a human hand

Rahonavis has historically been the subject of some uncertainty as to its proper taxonomic position – whether it is a member of the

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.[8]

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.[9] Norell and colleagues (2006) also found Rahonavis to lie within the Unenlagiinae, as the sister taxon to Unenlagia itself.[10] A 2007 study by Turner and colleagues again found it to be an unenlagiine dromaeosaurid, closely related to Unenlagia.[11]

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.[12] A cladistic analysis by Cau (2018) recovered Rahonavis as a probable relative of the long-tailed Early Cretaceous avialans Jeholornis and Jixiangornis.[13] 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.[14] In 2020, Rahonavis and the South American Overoraptor were found to be sister taxa in a clade sister to the Avialae.[15] As of 2020, it is undecided among paleontologists whether the paravian Rahonavis is an unenlagiine, a dromaeosaurid or an avialan.[7]

Paleobiology

Hypothetical life restoration

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

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.[3]

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."

deltoideus complexes seems to have been likely in R. ostromi.[12]

See also

References

  1. ^ Tudge, Colin (2009) The Bird:A Natural History of Who Birds Are, Where They Came From, and How They Live [1]
  2. ^ Holtz, Thomas R. Jr. (2008) Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages Supplementary Information
  3. ^
    ISBN 978-0-471-24723-4
    .
  4. PMID 9506938
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  5. S2CID 220097569
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  6. doi:10.1590/S0001-37652002000200023
    .
  7. ^
    S2CID 221507083
    .
  8. ^
    S2CID 11576813
    .
  9. S2CID 27078534. Supplementary information
    .
  10. hdl:2246/5823
    .
  11. PMID 17823350
    .
  12. ^ a b Agnolín, F.L.; Novas, F.E. (2013). "Avian ancestors. A review of the phylogenetic relationships of the theropods Unenlagiidae, Microraptoria, Anchiornis and Scansoriopterygidae". SpringerBriefs in Earth System Sciences. pp. 1–96.
  13. ^ Andrea Cau (2018). "The assembly of the avian body plan: a 160-million-year long process" (PDF). Bollettino della Società Paleontologica Italiana. 57 (1): 1–25. doi:10.4435/BSPI.2018.01.
  14. PMID 31333906
    .
  15. S2CID 218913199
    .

Further reading
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