Rahonavis

Live reconstruction of Rahonavis ostromi

• Madagascar, Mahajanga Province ( Maevarano Formation)

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

Rahonavis shows a mosaic of original features, which are typical for dromaeosauride dinosaurs, and of modern features as today's show birds. At first he was therefore one of the most primitive known bird, while many researchers now favor a classification within the dromaeosauriden dinosaurs. Maybe Rahonavis was capable of active flight.

Features

Rahonavis was a raven large lightweight predator with a long tail. The body length is estimated to be 70 cm and weight of 900 grams. The length of the thigh bone (femur), a key for length estimates size is 8.8 inches. Pneumatic cavities that were probably filled in the living animal with air bags to show up at the neck and back vertebrae. The sacrum ( sacrum ) consists of six vertebrae.

Rahonavis corresponds in some more features of the anatomy of today's birds as some very early birds such as Archaeopteryx: So the shoulder girdle was flexible and shows a mobile glenoid, in contrast to the fused, rigid shoulder girdle in Archaeopteryx. The forearm was greatly extended as in birds. Markers are at the Elle ( ulna ), which are likely to approach points of feathers ( quill knobs ), suggest at least 10 flight feathers - a typical number for today's birds. Forster ( 1998) noted that Rahonavis beat its wings with a larger amplitude than Archaeopteryx. The ilium ( ilium ) and the ischium ( ischium ) show distinct similarities with Archaeopteryx. In contrast to these modern features are original features which are typical of Dromaeosauriden how the enlarged sickle- claw on the second toe, the vertically oriented pubis ( pubic ) with characteristic boots or Hyposphen - Hypantrum connections of the vertebrae.

In particular, the arm bone and the shoulder girdle show adaptations to an active flying, although it remains unclear whether Rahonavis could actually fly. Chiappe and Dyke (2006) suggest that Rahonavis similar to Archaeopteryx and other long-tailed birds probably a weaker and less agile fliers than it is today living birds.

System

The systematic classification of this genus is disputed. Traditionally, it is regarded as a primitive bird and is considered a further indication of the close relationship between birds and dinosaurs. Some researchers such as spirit and Feduccia (2000) suggest that the found Rahonavis skeleton is a chimera: According to these researchers, the bird-like arm bones actually belong to a bird, while the rear parts of the skeleton belonged to a small theropod, whereupon the many original features of this bone indicate. Already the describer of Rahonavis noted that a chimera can not be excluded, also because in the same quarry in close proximity to a Rahonavis - locality wingless fossil of the primitive bird Vorona was discovered. However, many other scientists, including Erstbeschreiber continue to assume that all the bones of the Rahonavis - discovery belong to the same animal. Chiappe (2007), the hypothesis of a chimera also back and noticed that all the bones of the Rahonavis - discovery were found in an area that is " smaller than a sheet of paper ."

Makovicky and colleagues ( 2005) make the assignment to the birds in question and assign Rahonavis as close relatives of Dromaeosauriden Unenlagia and Buitreraptor within the basal Dromaeosauriden subfamily Unenlagiinae one, which was limited to the southern continents. Turner, Hwang and Norell (2007 ) Ascending Rahonavis also Unenlagiinen as a - as a sister taxon of Unenlagia. Other studies confirm the classification as Unenlagiine.

Fund and naming

The only known skeleton ( copy number UA 8656 ) comes from a quarry near Berivotra in Madagascar Mahajanga Province. Stratigraphically the Fund comes from the Maevarano formation, a rich fossil site in north-west Madagascar. Other theropods this formation include the Cerato dinosaur Majungasaurus and Masiakasaurus with a. The skeleton was discovered in 1995 Rahonavis by a joint expedition of the State University of New York and the University of Antananarivo during the excavation of a Titanosaurier skeleton between the bones of this much larger dinosaur. Collecting fossils in the region difficult due to the dense grass to be difficult - the bones of the Titanosauriers could be localized only after a bushfire. The skeleton consists of the fuselage, parts of the arms and shoulder girdle, the hind legs and parts of the tail.

The skeleton was described in 1998 by Forster and colleagues as RAHONA ostromi scientifically. Shortly after the release of the specification changed the descriptor the generic name in Rahonavis, because it has been found that the name RAHONA was already assigned to a Madagascar moth of the family of Trägspinner ( Lymantriidae ). The name Rahonavis means " threat from the clouds " and is derived from RAHONA (Malagasy for " threat ", " cloud" ) and avis ( " bird" ) from. The species name honors John ostromi Ostrom, a prominent American paleontologist, who has rendered outstanding services for the exploration of Dromaeosauriden and the theory revived that birds descended from dinosaurs.