Bagaraatan
- Ömnö Gobi Aimag, Mongolia ( Nemegt Formation)
- Bagaraatan ostromi
Bagaraatan is a genus theropod dinosaur from the Upper Cretaceous of Mongolia. So far, a single fragmentary skeleton is known, which was scientifically described in 1996 by Halszka Osmólska with the only kind Bagaraatan ostromi. Bagaraatan was a medium-sized, bipedal carnivore with a relatively small head and slender hind legs. From other theropods he differed by the very unusual anatomy of the vertebrae of the tail, which has a fairly rigid tail result. Maybe Bagaraatan belongs to the group of Tyrannosauroidea.
Characteristics and biomechanics
Bagaraatan is estimated by Osmólska (1996 ) to a length of 3 to 3.5 meters and a hip height of less than one meter, so Bagaraatan was about as big as large Deinonychus copies. The degree of fusion and ossification of various skeletal parts indicates that it has acted in the Fund to an adult, and maybe even old individual. The total length of the jaw estimates Osmólska to 23 to 24 inches; this estimate is based on comparisons with the pines Dromaeosauridae that show a similar jaw morphology according Osmólska. This suggests a relatively small skull. The jaw was massive, but slender; the rear (post dental ) part was quite deep. The hips showed a very strong muscles. The hind legs were slender, suggesting a long-legged, fairly agile predator or scavenger. The tail was relatively rigid, whereupon strongly developed Hyposphen - Hypantrum connections - mechanical connecting elements of the vertebrae - indicate. So Osmólska suspected that larger movements of the tail in vertical and horizontal direction only by a few, to the sacrum subsequent vortex could be exercised while the tail was rigid in itself. The rigid tail might have been an adaptation to fast running.
In spite of the skeleton only fragmentary Osmólska could set up a number of diagnostic features by which should distinguish the genus from other genera: in addition to unusual features of the caudal vertebrae, such as the very strong Hyposphen - Hypantrum complexes example, these are the two Surangular - Foramia ( openings ) of the lower jaw, the hollow, very thin tail vortex centers, and the ilium, which shows two depressions and a comb-like extension on the lateral surface of Postacetabularprozesses.
History of discovery, naming and paleoecology
The incomplete skeleton ( holotype, specimen number ZPAL MgD-I/108 ) was discovered in 1970 by Zofia Kielan - Jaworowska during a Polish- Mongolian expedition in a known good Nemegt -locality reference in the eastern part of the Northern Sayr. Stratigraphically the Fund comes from the lower portion of Nemegt lineup. Osmólska indicates that the rock of the discovery site could have come from the middle Maastrichtian, is thus about 67 million years old; this information is, however, uncertain. In the position in which the bones were, as they have been discovered, all the lay bone before said basin. 21 of the 25 received caudal vertebrae are preserved articulated as a series. All bones were found severely weathered.
For the scientific description of the genus Osmólska chose the name Bagaraatan, which translates as "little robber " means (Mongolian baga - "small"; araatan - " robber ", " predator "). The specific epithet honors ostromi John Ostrom, an eminent paleontologist.
It an incomplete left lower jaw were found, which the central part and the tooth crowns missing, 25 caudal vertebrae of the middle and anterior part of the tail, including some chevron bones, pelvic bones including parts of the left and right iliac bone ( ilium ), the right and left ischium ( ischium ) and the upper half of the left pubis ( pubic ) and the left hind leg, without the majority of the foot up to the toe members II and IV -2 -1.
Bagaraatan was in his description already the twelfth theropod species that was detected from the Nemegt lineup. This shows that the diversity of theropods in the Nemegt fauna was exceptionally high. Other theropod genera of Nemegt lineup include, for example Therizinosaurus, Tarbosaurus, Elmisaurus, Oviraptor, Gallimimus and Avimimus with a.
System
The systematic classification of this genus is uncertain. Shortly after the skeleton was discovered, it designated Gradziński and Jerzykiewicz (1972 ) in a summary of the results of the expedition of 1970 as " coeluroid dinosaur " ( coeluriden dinosaurs) - Today the Coeluridae is considered paraphyletic and hence invalid. Osmólska (1996 ) Bagaraatan only describe as unspecified assignable representatives of Tetanurae, one of two main branches of the theropods, but fails due to the fragmentary finds a more accurate classification. Subsequent classification experiments are somewhat exclusive; so there Holtz (2000) one belonging to the Coelurosauria and Rauhut (2003) one belonging to the Maniraptora on, both subgroups of Tetanurae. Holtz (2004) holds a membership in the Tyrannosauroidea likely, a group that is within the Tetanurae and Coelurosauria, but outside of the Maniraptora.