Rahonavis

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Rahonavis
Live reconstruction of Rahonavis ostromi

Live reconstruction of Rahonavis ostromi

Temporal occurrence
Upper Cretaceous ( Maastrichtian )
72 to 66 million years
Locations
Systematics
Lizard dinosaur (Saurischia)
Theropoda
Deinonychosauria
Dromaeosauridae
Unenlagiinae
Rahonavis
Scientific name
Rahonavis
Forster , Sampson , Chiappe & Krause , 1998
Art

Rahonavis is a genus of theropod dinosaur from the group of Dromaeosauridae . So far only a single fragmentary skeleton is known, which was found in the province of Mahajanga in Madagascar and comes from the late Upper Cretaceous ( Maastrichtian ). The only known species is Rahonavis ostromi .

Rahonavis shows a mosaic of original features, typical of dromaeosaurid dinosaurs, and modern features, like those of today's birds . In the beginning he was therefore one of the most original known birds, while many researchers now favor classification within the dromaeosaurid dinosaurs. May have been Rahonavis capable of active flight.

features

Rahonavis was a raven-sized, light-weight predator with a long tail. The body length is estimated at 70 centimeters and the weight at 900 grams. The length of the thigh bone (femur), an important parameter for length estimates, is 8.8 centimeters. Pneumatic cavities, which in living animals were probably filled with air sacs , can be seen in the cervical and dorsal vertebrae. The sacrum consists of six vertebrae.

Rahonavis corresponds in some features more to the anatomy of today's birds than some very early birds like Archeopteryx : The shoulder girdle was flexible and shows a mobile glenoid, in contrast to the fused, rigid shoulder girdle of Archeopteryx . As in birds, the forearm was greatly elongated. Marks on the Elle (ulna), which are probably are insertions of feathers (quill knobs) can include at least 10 flight feathers - typical of today's birds number. Forster (1998) notes that Rahonavis could flap its wings with a greater amplitude than Archeopteryx . The iliac (ilium) and the ischial (ischium) show clear similarities with Archeopteryx . In contrast to these modern features, there are original features that are typical of dromaeosaurids, such as the enlarged sickle claw on the second toe, the vertically aligned pubis with its characteristic boot or the hyposphere-hypantrum connections of the vertebrae.

The arm bones and shoulder girdle in particular show adaptations to active flight, although it remains unclear whether Rahonavis was actually able to fly. Chiappe and Dyke (2006) suggest that Rahonavis , like Archeopteryx and other long-tailed birds, was probably a weaker and less agile flier than birds alive today.

Systematics

The systematic classification of this genus is controversial. It is traditionally considered a primitive bird and is another indication of the close relationship between birds and dinosaurs. Some researchers such as Geist and Feduccia (2000) suspect that the Rahonavis skeleton that was found represents a chimera : According to these researchers, the bird-like arm bones actually belong to a bird, while the rear skeletal parts belonged to a small theropod, whereupon the many original features of these bones indicate. The first person to describe Rahonavis noted that a chimera cannot be ruled out, also because a wingless fossil of the primitive Vorona bird was discovered in the same quarry in the immediate vicinity of the Rahonavis site . However, many other scientists, including the first describer, continue to assume that all the bones of the Rahonavis find belong to the same animal. Chiappe (2007) also rejects the hypothesis of a chimera and notes that all of the bones in the Rahonavis find were found on an area “smaller than a sheet of paper”.

Makovicky and colleagues (2005) question the assignment to birds and classify Rahonavis as close relatives of the dromaeosaurids Unenlagia and Buitreraptor within the basal dromaeosaurid subfamily Unenlagiinae , which was restricted to the southern continents . Turner, Hwang and Norell (2007) also classify Rahonavis as Unenlagiinen - as the sister taxon of Unenlagia . Further studies confirm the classification as an inconvenience.

Find and naming

The only known skeleton (copy number UA 8656) comes from a quarry near Berivotra in the Malagasy province of Mahajanga. Stratigraphically , the find comes from the Maevarano Formation , a rich fossil deposit in northwest Madagascar. Other theropods of this formation include the ceratosaurs Majungasaurus and Masiakasaurus . The Rahonavis skeleton was discovered in 1995 by a joint expedition from the State University of New York and Antananarivo University while excavating a titanosaur skeleton between the bones of this much larger dinosaur. Collecting fossils in the region is difficult because of the dense grass - the titanosaur's bones could only be located after a bush fire. The skeleton consists of the trunk, parts of the arms and the shoulder girdle, the hind legs and parts of the tail.

The skeleton was scientifically described by Forster and colleagues as Rahona ostromi in 1998 . Shortly after the description was published, the descriptor changed the genus name to Rahonavis , because it turned out that the name Rahona was already given to a Malagasy moth from the family of bearer moths (Lymantriidae). The name Rahonavis means something like "threat from the clouds" and is derived from Rahona ( Malagasy for "threat", "cloud") and avis ("bird"). The species name ostromi honors John Ostrom , an eminent American paleontologist who did a great job researching the dromaeosaurids and revived the theory that birds descended from dinosaurs.

Web links

Commons : Rahonavis  - collection of images, videos and audio files

Individual evidence

  1. a b c Alan H. Turner, Diego Pol, Julia A. Clarke, Gregory M. Erickson, Mark A. Norell : A Basal Dromaeosaurid and Size Evolution Preceding Avian Flight. In: Science . Vol. 317, No. 5843, 2007, pp. 1378-1381, doi : 10.1126 / science.1144066 , digitized version (PDF; 507.41 kB) , Supporting Online Material (PDF; 755.11 kB) .
  2. ^ A b c Catherine A. Forster, Scott D. Sampson, Luis M. Chiappe , David W. Krause: The Theropod Ancestry of Birds: New Evidence from the Late Cretaceous of Madagascar. In: Science . Vol. 279, No. 5358, 1998, pp. 1915-1919, doi : 10.1126 / science.279.5358.1915 .
  3. a b Kevin Padian : Basal Avialae. In: David B. Weishampel , Peter Dodson , Halszka Osmólska (eds.): The Dinosauria . 2nd edition. University of California Press, Berkeley CA et al. 2004, ISBN 0-520-24209-2 , pp. 196-209.
  4. ^ A b c Luis M. Chiappe, Gareth J. Dyke : The early evolutionary history of birds. In: Journal of the Paleontological Society of Korea. Vol. 22, No. 1, 2006, ISSN  1225-0929 , pp. 133–151, digitized version (PDF; 697.54 kB) .
  5. ^ A b Nicholas R. Geist, Alan Feduccia: Gravity-defying Behaviors: Identifying Models for Protoaves. In: American Zoologist. Vol. 40, No. 4, 2000, ISSN  0003-1569 , pp. 664-675, doi : 10.1668 / 0003-1569 (2000) 040 [0664: GDBIMF] 2.0.CO; 2 , digitized version (PDF; 2.39 MB) .
  6. Luis M. Chiappe: Glorified Dinosaurs. The Origin and Early Evolution of Birds. UNSW Press et al., Sydney 2007, ISBN 978-0-86840-413-4 .
  7. ^ Peter J. Makovicky , Sebastián Apesteguía, Federico L. Agnolín: The earliest dromaeosaurid theropod from South America. In: Nature . Vol. 437, No. 7061, 2005, pp. 1007-1011, doi : 10.1038 / nature03996 .
  8. ^ Alan H. Turner, Sunny H. Hwang, Mark A. Norell: A small derived theropod from Öösh, Early Cretaceous, Baykhangor Mongolia (= American Museum Novitates. No. 3557). American Museum of Natural History, New York NY 2007, online .
  9. Fernando E. Novas , Diego Pol, Juan I. Canale, Juan D. Porfiri, Jorge O. Calvo : A bizarre Cretaceous theropod dinosaur from Patagonia and the evolution of Gondwanan dromaeosaurids. In: Proceedings of the Royal Society. Series B: Biological Sciences. Vol. 276, No. 1659, pp. 1101-1107, doi : 10.1098 / rspb.2008.1554 .
  10. ^ Catherine A. Forster, Scott D. Sampson, Luis M. Chiappe, David W. Krause: Genus Correction. In: Science. Vol. 280, No. 5361, 1998, p. 179, doi : 10.1126 / science.280.5361.179g .
  11. Ben Creisler: Dinosauria Translation and Pronunciation Guide. Archived from the original on July 20, 2011 ; Retrieved December 3, 2013 .