Shanag
| Shanag | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Lower Cretaceous ( Hauterivium to Barremium ) | ||||||||||||
| 133.9 to 126.3 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Shanag | ||||||||||||
| Turner et al. , 2007 | ||||||||||||
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Shanag is a genus of theropod dinosaur from the group of Dromaeosauridae . So far, only the jaw bone are known from the Lower Cretaceous of Mongolia come. The only species, Shanag ashile , was found by Turner et al. described . It was a very small, two-legged carnivore .
features
The only find consists of the right upper jaw (maxilla), the dental (the tooth-bearing part of the lower jaw ) and a fragmentary splenial, which were discovered in the anatomical network.
Shanag was a very small theropod: comparisons with the better-known Microraptor zhaoianus suggest that the specimen found was around 45 cm long and weighed 200 g during its lifetime.
Autapomorphies , i.e. characteristics by which the genus can be clearly distinguished from other dromaeosaurids, are the lack of a promaxillary window and chambers between the alveoli (tooth sockets). However, these chambers were not part of the air sac system , but were surrounded on all sides by a thin bone wall - they are only visible in the fossil found because the lateral surface of the upper jaw has decomposed. Shanag shows a mosaic of features that are typical of dromaeosaurids or birds. Characteristics typical of birds can be seen, for example, on the upper jaw, which, like most birds, is triangular and tapers to the rear. The large antorbital depression (fossa) extends over most of the lateral surface of the upper jaw. The maxillary window is oval and relatively large and, similar to other dromaeosaurids, is located fairly high on the upwardly directed process (ramus) of the upper jaw. The dental is straight, long and thin, with the height being only 12% of the length.
The found right upper jaw shows at least nine alveoli, six of which still contain teeth. A special feature are the very long roots of the three middle teeth of the upper jaw, which make up about 70% of the entire tooth length. The tooth roots of two teeth are exposed in the found fossil. The lower jaw showed at least 15 teeth that were more tightly packed and smaller than the teeth of the upper jaw.
Systematics
While Turner et al. Shanag initially described as a close relative of Sinornithosaurus , they assign the genus to the group Unenlagiinae ( Buitreraptor , Rahonavis , Unenlagia ) in a later study . According to the researchers, the Unenlagiinae together with the dromaeosaurids of the Jehol group ( Microraptor , Graciliraptor , Sinornithosaurus ) form a sister group to the more advanced dromaeosaurids, which include the velociraptorins and related forms.
Find and naming
The only find, a skull fragment (copy number IGM 100/1119), was discovered in 1999 by a joint expedition of the Mongolian Academy of Sciences and the American Museum of Natural History in Öösh, a site in the Altai region of central Mongolia. The debris is from the Lower Cretaceous, making it roughly the same age as the rich formations of the Jehol group in China , known for their feathered dinosaurs , although the exact age is unknown. Öösh is known for rich finds of the ceratopsier Psittacosaurus mongoliensis as well as of sauropods. Theropod remains are rare in Öösh - at the time of Shanag's description , the only described theropod find from Öösh was “ Prodeinodon ” (Osborn, 1924), which is based on large but undiagnosed teeth.
The name of the genus refers to the Shanag, black-headed dancers of the Buddhist Tsam festival. The Artepitheth ashile points to the old name of Öösh-reference, as described by Henry Fairfield Osborn was used.
literature
Unless otherwise noted, all information comes from the following work:
- 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 .
Individual evidence
- ↑ 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) .