Rahonavis

Taxobox
name = "Rahonavis"

---

fossil_range = fossil_range|84|71| Late Cretaceous
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Saurischia
subordo = Theropoda
familia = Dromaeosauridae
genus = "Rahonavis"
genus_authority = Forster "et al.", 1998b
subdivision_ranks = Species
subdivision =
*"R. ostromi" (Forster "et al.", 1998a [originally "Rahona"] ) (type)
synonyms =
*"Rahona" Forster "et al.", 1998a preoccupied by Griveaud, 1975

"Rahonavis" [Etymology: approximately "cloud menace bird": "Rahonavis", from Malagasy "rahona" (RA-hoo-na, "cloud" or "menace") + Latin "avis" "bird". Specific name "R. ostromi", dedicated to John Ostrom.] is a genus of dinosaur from the Late Cretaceous (Campanian?, 83.5 - 70.6 mya) of what is now northwestern Madagascar. It is known from a partial skeleton (UA 8656) found in Maevarano Formation rocks at a quarry near Berivotra, Mahajanga Province.

Description

"Rahonavis" was a small predator, about the size of "Archaeopteryx", with the typical "Velociraptor"-like raised sickle claw on the second toe.

Classification

"Rahonavis" has historically been the subject of some uncertainty as to its proper taxonomic position - whether it is a member of the clade Aves or a closely-related dromaeosaurid. The presence of quill knobs on its ulna (forearm bone) led initially to its inclusion among the birds; however, the rest of the skeleton is rather typically dromaeosaurid in its attributes. Given the extremely close affinities between primitive 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 Aves, but while the pelvis shows adaptations to flight similar in function to those of "Archaeopteryx", they seem to be independently derivedcite journal|last=Geist|first= Nicholas R.|coauthors= Alan Feduccia|year=2000|title=Gravity-defying Behaviors: Identifying Models for Protoaves|journal=American Zoologist|issue=40|pages=pp. 664–675|doi=10.1668/0003-1569(2000)040 [0664:GDBIMF] 2.0.CO;2|doilabel=10.1668/0003-1569(2000)040[0664:GDBIMF]2.0.CO;2|volume=40 [http://icb.oxfordjournals.org/cgi/reprint/40/4/664.pdf#search=%22Gravity-defying%20Behaviors%3A%20Identifying%20Models%20for%20Protoaves%22 PDF fulltext] .] . Alternately, Makovicky and colleagues considered "Rahonavis" to be closely related to the South American dromaeosaurids "Unenlagia" and "Buitreraptor", and thus a member of the subfamily Unenlagiinaecite book|last=Makovicky|first=Peter J.|coauthors= Apesteguía, Sebastián & Agnolín, Federico L. |year=2005|title=The earliest dromaeosaurid theropod from South America|journal=Nature|issue=437|pages=pp. 1007-1011 DOI|10.1038/nature03996. (HTML abstract). [http://www.nature.com/nature/journal/v437/n7061/suppinfo/nature03996.html Supplementary information] .] . Norell and colleagues (2006) also found "Rahonavis" to lie within the Unenlagiinae, as the sister taxon to "Unenlagia" itselfcite journal|last=Norell|first=M.A.|coauthors= Clark, J.M.; Turner, A.H.; Makovicky, P.J.; Barsbold, R. and Rowe, T. |year=2006|title=A new dromaeosaurid theropod from Ukhaa Tolgod (Omnogov, Mongolia)|journal=American Museum Novitates|issue=3545|pages=pp. 1–51|doi=10.1206/0003-0082(2006)3545 [1:ANDTFU] 2.0.CO;2|doilabel=10.1206/0003-0082(2006)3545[1:ANDTFU]2.0.CO;2|volume=3545] . A 2007 study by Turner and colleagues again found it to be an unenlagiine dromaeosaurid, closely related to "Unenlagia"cite journal |last=Turner |first=Alan H. |coauthors= Pol, Diego; Clarke, Julia A.; Erickson, Gregory M.; and Norell, Mark |year=2007 |title=A basal dromaeosaurid and size evolution preceding avian flight |url=http://www.sciencemag.org/cgi/reprint/317/5843/1378.pdf |format=pdf |journal=Science |volume=317 |pages=1378–1381 |doi=10.1126/science.1144066 ] .

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 mothscite journal|last=Forster|first=Catherine A.|coauthors= Sampson, Scott D.; Chiappe, Luis M. & Krause, David W.|year=1998a|title=The Theropod Ancestry of Birds: New Evidence from the Late Cretaceous of Madagascar|journal=Science|issue=5358|pages=pp. 1915–1919 DOI|10.1126/science.279.5358.1915. (HTML abstract).] cite journal|last=Forster|first=Catherine A.|coauthors=Sampson, Scott D.; Chiappe, Luis M. & Krause, David W. |year=1998b|title=Genus Correction.|journal=Science|voumel=280|issue=5361|pages=p. 179] .

Discovery and species

The fossilized remains of "Rahonavis" were first recovered 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 mid-Cretaceous sediments (Albian/Cenomanian, c. 100-99 mya) of the Kem Kem region, 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"cite journal|last=Riff|first=Douglas|coauthors=Kellner, Alexander W. A.; Mader, Bryn & Russell, Dale |year=2002|title=On the occurrence of an avian vertebra in Cretaceous strata of Morocco, Africa|journal=Anais da Academia Brasileira de Ciências|issue=74|pages=pp. 367–368|volume=2 DOI|10.1590/S0001-37652002000200023. [http://www.scielo.br/pdf/aabc/v74n2/a23v74n2.pdf PDF fulltext] .] .

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 arecite book|last=Chiappe|first= L.M.|title=Glorified Dinosaurs: The Origin and Early Evolution of Birds|location=Sydney|publisher=UNSW Press] . 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.

References

*cite journal|last= Forster|first=Catherine A.|coauthors=O'Conner|year=2000|title=The avifauna of the Upper Cretaceous Maevarano Formation, Madagascar|journal=Journal of Vertebrate Paleontology|issue=20|volume=3|pages=pp. 41A–42A
*cite journal|last=Schweitzer|first=Mary H.|coauthors=Watt, John A.; Avci, Recep; Forster, Catherine A.; Krause, David W.; Knapp, Loren; Rogers, Raymond R.; Beech, Iwona & Marshall, Mark |year=1999|title=Keratin immunoreactivity in the Late Cretaceous bird "Rahonavis ostromi"|journal=Journal of Vertebrate Paleontology|issue= 19|volume=4|pages=pp. 712–722 [http://www.vertpaleo.org/jvp/19-712-722.html HTML abstract] .