Bagaraatan

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Bagaraatan
Temporal occurrence
Campanium to Maastrichtian ( Upper Cretaceous )
83.5 to 65.5 million years
Locations
Systematics
Lizard dinosaur (Saurischia)
Theropoda
Tetanurae
Coelurosauria
Tyrannosauroidea
Bagaraatan
Scientific name
Bagaraatan
Osmólska , 1996
Art
  • Bagaraatan ostromi

Bagaraatan is a genus theropod dinosaur from the Upper Cretaceous of Mongolia . So far, a single fragmentary skeleton is known, which wasscientifically described by Halszka Osmólska in 1996with the only species Bagaraatan ostromi . Bagaraatan was a medium-sized, two-legged carnivore with a relatively small head and slender hind legs. It differed from other theropods in particular by the very unusual anatomy of the caudal vertebrae, which resulted in a rather rigid tail. Bagaraatan possibly belongsto the group of the Tyrannosauroidea .

Features and biomechanics

Bagaraatan is estimated by Osmólska (1996) to be 3 to 3.5 meters in length and less than one meter at the waist, making Bagaraatan about the same size as large Deinonychus specimens. The degree of fusion and ossification of various parts of the skeleton indicates that the find was a fully grown, and perhaps even an old individual. Osmólska estimates the total length of the jaw to be 23 to 24 centimeters; this estimate is based on comparisons with pines of the Dromaeosauridae , which, according to Osmólska, show a similar pine morphology. This suggests a relatively small skull. The jaw was massive but slender; the rear (post-dental) part was quite deep. The hips showed very strong muscles. The hind legs were slim, which suggests a long-legged, quite agile predator or scavenger. The tail was relatively stiff, as indicated by strongly developed hyposphene-hypantrum connections - mechanical connecting elements of the vertebrae. Osmólska suspects that larger movements of the tail in the vertical and horizontal direction could only be exerted by a few vertebrae adjacent to the sacrum , while the tail itself remained rigid. The rigid tail could have been an adaptation for fast running.

In spite of the only fragmentary preserved skeleton, Osmólska was able to establish a number of diagnostic features with which the genus is to be distinguished from other genera: In addition to unusual features on the caudal vertebrae such as the very strong hyposphene-hypantrum complexes, these are, for example, the two surangular foramia ( Openings) of the lower jaw, the hollow, very thin-walled caudal vertebrae centers, and the iliac bone, which shows two depressions and a comb-like process on the lateral surface of the post-acetabular process.

History of discovery, naming and paleoecology

fossil jawbones from Bagaraatan

The incomplete skeleton ( holotype , copy number ZPAL MgD-I / 108) was discovered in 1970 by Zofia Kielan-Jaworowska during a Polish-Mongolian expedition in a site known as the Nemegt site in the eastern part of the Northern Sayr . Stratigraphically , the find comes from the lower section of the Nemegt formation . Osmólska states that the rock at the site could have come from the central Maastrichtian , i.e. is about 67 million years old; however, this information is uncertain. In the position the bones were in when they were discovered, all of the bones were in front of the pelvis. 21 of the 25 obtained caudal vertebrae are articulated as a series. All bones were found badly weathered.

For the scientific description of the genus Osmólska chose the name Bagaraatan , which means something like "little robber" ( Mongolian baga - "small"; araatan - "robber", "predator"). The specific epithet ostromi honors John Ostrom , an important paleontologist .

An incomplete left lower jaw was found, missing the middle part and the tooth crowns, 25 caudal vertebrae of the middle and front part of the tail including some chevron bones , pelvic bones including parts of the left and right ilium , the right and left ischium ( Ischium) and the upper half of the left pubis , as well as the left hind leg without most of the foot except for the phalanges II-2 and IV-1.

Bagaraatan was already the twelfth theropod species to be identified from the Nemegt formation when it was described. This shows that theropod diversity in the Nemegt fauna was exceptionally high. Other theropod genera of the Nemegt formation include, for example, Therizinosaurus , Tarbosaurus , Elmisaurus , Oviraptor , Gallimimus, and Avimimus .

Systematics

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 thus invalid. Osmólska (1996) describes Bagaraatan only as a representative of the Tetanurae , one of the two main branches of the theropods, which cannot be identified in detail, but omits a more precise classification due to the fragmentary finds. Later attempts at classification are somewhat more exclusive; so Holtz (2000) indicates a membership in the Coelurosauria and Rauhut (2003) a membership in the Maniraptora , both subgroups of the Tetanurae. Holtz (2004) believes it is likely to belong to the Tyrannosauroidea , a group that is within the Tetanurae and Coelurosauria, but outside of the Maniraptora.

literature

Web links

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

Individual evidence

  1. ↑ Ryszard Gradzifiski, Tomasz Jerzykiewicz: Additional geographical and geological data from the Polish-Mongolian palaeontological expeditions . In: Palaeontologia Polonica. Vol. 27, 1972, ISSN  0078-8562 , pp. 17-32, (PDF; 1.1 MB).
  2. ↑ Bagaraatan - Basic Info. In: The Paleobiology Database. Retrieved May 25, 2010 .
  3. ↑ Thomas R. Holtz Jr .: Tyrannosauroidea. 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. 111-136.