Rahonavis
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Extinct (fossil)
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| Rahonavis ostromi (C. A. Forster, Sampson, Chiappe & Krause, 1998a) | ||||||||||||||||||||||
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Rahonavis<ref> Rahonavis, from Malagasy rahona (RA-hoo-na, "cloud" or "menace") and Latin avis "bird". ostromi, dedicated to John Ostrom.</ref> is a dinosaur from the Late Cretaceous (Campanian?, 70.6 - 83.5 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.
It is the subject of some controversy as to its proper taxonomic position--whether it is a member of the crown clade Aves or a closely-related dromaeosaur. The presence of what have been interpreted to be quill knobs on its ulna 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 dromaeosaur cousins, along with the possibility that flight may have developed and been lost multiple times among these groups, it may be impossible to place Rahonavis firmly among or outside the birds. At this point, the controversies regarding the relative relationships among birds, dromaeosaurs, and troodontids are numerous and change with each new feathered fossil discovery. Makovicky et al. (2005) consider Rahonavis to be closely related to the South American dromaeosaurs Unenlagia and Buitreraptor, and thus a member of the subfamily Unenlagiinae (this is the position used in the taxobox here). It may actually be closer to Archaeopteryx, as originally suggested by the describers, and thus a member of Class Aves, Order Archaeopterygiformes, but while the pelvis shows adaptations to flight similar in function to those of Archaeopteryx, they seem to be independently derived (Geist & Feduccia, 2000).
What is clear from the remains is that the living Rahonavis was a small predator, about the size of Archaeopteryx, with the typical Velociraptor-like raised sickle claw on the second toe. Its discoverers (Forster et al., 1998a) initially named it Rahona but changed the name after discovering that the name Rahona was already assigned to a genus of lymantriid moths (Forster et al., 1998b). 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. Its discoverers are convinced that it does, while others would rather consider Rahona as described a nomen dubium (Geist & Feduccia, 2000). The nearby discovery of the primitive bird Vorona berivotrensis at least shows that the possibility of a mix-up cannot be fully excluded. Indeed, the "raptor" claw of Rahonavis is not infrequently ascribed to Vorona in error.
[edit] References
- Makovicky, Peter J.; Apesteguía, Sebastián & Agnolín, Federico L. (2005): The earliest dromaeosaurid theropod from South America. Nature 437: 1007-1011. DOI:10.1038/nature03996 (HTML abstract) Supplementary information
- Forster, Catherine A.; Sampson, Scott D.; Chiappe, Luis M. & Krause, David W. (1998a): The Theropod Ancestry of Birds: New Evidence from the Late Cretaceous of Madagascar. Science 279(5358): 1915-1919. DOI:10.1126/science.279.5358.1915 (HTML abstract)
- Forster, Catherine A.; Sampson, Scott D.; Chiappe, Luis M. & Krause, David W. (1998b): Genus Correction. Science 280(5361): 179.
- Forster, Catherine A. & O'Conner (2000): The avifauna of the Upper Cretaceous Maevarano Formation, Madagascar. J. Vertebr. Paleontol. 20(3): 41A-42A.
- Geist, Nicholas R. & Feduccia, Alan (2000): Gravity-defying Behaviors: Identifying Models for Protoaves. American Zoologist 40: 664–675. PDF fulltext
- Schweitzer, Mary H.; Watt, John A.; Avci, Recep; Forster, Catherine A.; Krause, David W.; Knapp, Loren; Rogers, Raymond R.; Beech, Iwona & Marshall, Mark (1999): Keratin immunoreactivity in the Late Cretaceous bird Rahonavis ostromi. J. Vertebr. Paleontol. 19(4), 712-722. HTML abstract
[edit] Footnotes
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