Alioramus
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The skull of Alioramus remotus |
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| Upper Cretaceous ( Maastrichtian ) | ||||||||||||
| 72 to 66 million years | ||||||||||||
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| Alioramus | ||||||||||||
| Kurzanov , 1976 | ||||||||||||
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Alioramus ("other branch", from Latin alius "different" and ramus "branch") is a genus of theropod dinosaur from the Upper Cretaceous Asia , which is one of the Tyrannosauridae .
So far, two skeletal finds from Mongolia are known that come from the Maastrichtian (approx. 72 to 66 million years ago) and are attributed to two different species: the type species Alioramus remotus and the species Alioramus altai described in 2009 . The relationship to other genera of the Tyrannosauridae is unclear, but some experts believe that Alioramus is closely related to the contemporary Tarbosaurus , or even a juvenile synonym of this genus.
Alioramus was a relatively small and graceful tyrannosaur, which was characterized by a long snout with a row of five bony bumps on the top. Furthermore, Alioramus shows more teeth than any other tyrannosaurid.
features
The first skeleton was described by the Russian paleontologist Sergei Kurzanov in 1976 as Alioramus remotus . Kurzanov estimates this specimen to be five to six meters long. The ontogenetic stage of this individual is controversial, which is why it could also be a young animal . The partial skull of this specimen was compressed during fossilization and was approximately 18 inches long. The skull was long and flat; a trait that is often found in basal (original) tyrannosauroids and in the young of larger tyrannosaurids.
The pair of nasal bones was fused and provided with a series of five irregular, bony bumps that ran along the seam of the nasal bone. These bumps are all over an inch high. On the fused parietal bone (parietal) at the back of the head sat a transversely oriented protrusion, the so-called nuchal ridge , which all tyrannosaurids have in common. In Alioramus the nuchal ridge is significantly thickened, similar to that of Tarbosaurus and Tyrannosaurus . Like the rest of the skull, the lower jaws were long and thin, another feature that could possibly indicate a juvenile. As with Tarbosaurus, the lower jaw is characterized by a ridge on the outer surface of the angular bone, which is hooked to the back of the dentals , which means that the jaw does not have the flexibility that can be seen in other tyrannosaurids. Other tyrannosaurids had four teeth on each side of the paired intermaxillary bone that were "D" -shaped in diameter. Including the 16 or 17 teeth in each half of the upper jaw and the 18 teeth in each half of the lower jaw, Alioramus had a total of 76 to 78 teeth, more than any other tyrannosaurid.
After the discovery of Yutyrannus , a 9 meter long tyrannosaurid that was completely covered with down feathers , it is very likely that Alioramus also had a plumage.
Systematics
Paleontologists classify Alioramus within the superfamily Tyrannosauroidea , but a more precise classification remains controversial because of the sparse remains. According to a cladistic analysis from 2003, Alioramus can be classified within the family Tyrannosauridae and the subfamily Tyrannosaurinae together with Tyrannosaurus , Tarbosaurus and Daspletosaurus . Another study from 2004 supports this result, but notes that a position outside of the Tyrannosauridae is similarly probable, although the characteristics, which are often interpreted as juvenile, could also reflect a basal position within the Tyrannosauroidea. Another study does not consider Alioramus because of the few fossils. Brusatte and colleagues, who described another species with Alioramus altai in 2009 , however, also come to the conclusion that Alioramus must be classified within the Tyrannosauridae and the Tyrannosaurinae.
Tarbosaurus and Alioramus share various skull features, including a hook mechanism between the bones of the lower jaw. Both genera lack the point on the nasal bone that connects the nasal bone with the tearbone (lacrimale) - this point is found in all other tyrannosaurids except for adult Daspletosaurus . The two genera are perhaps closely related and represent an Asiatic branch of the Tyrannosauridae. Some specimens of Tarbosaurus show a series of bumps on the nasal bone, similar to the humps of Alioramus , only much lower. The long and flat shape of the Alioramus remotus skull suggests, according to some researchers, that the individual was not yet sexually mature when it died. Sometimes it is even suspected that it is a juvenile Tarbosaurus that lived in the same place at the same time. However, the more pronounced cusps on the nasal bone and the higher number of teeth on Alioramus suggest a separation of the two taxa , even if it were a young animal. In addition, finds from not yet sexually mature Tarbosaurus individuals show the same number of teeth as adult Tarbosaurus individuals. The discovery of the second species Alioramus altai confirms the differentiation of Alioramus from other tyrannosaurid genera.
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Cladogram of the Tyrannosauridae according to Holtz, 2004
| Tyrannosauridae |
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Alternative cladogram of the Tyrannosauridae according to Currie and others 2003
Discovery history and naming
The type material ( PIN 3141/1) of Alioramus remotus is a partial skull that was found together with three metatarsal bones. A joint expedition by the Soviet Union and Mongolia found these remains in the Gobi Desert in the early 1970s ; the site is known as Nogon-Tsav and is in Bajanchongor-Aimag .
The Russian paleontologist Sergei Kurzanov described the find in 1976. The humps and the flat skull demarcate this animal so clearly from other tyrannosaurids that Kurzanov believed his find was only distantly related to other members of the Tyrannosauridae. Accordingly, he named the genus Alioramus , from the Latin words alius "different" and ramus "branch", and the species A. remotus , which also comes from Latin and means "to remove".
The Alioramus altai , described in 2009 by Brusatte, Carr, Erickson, Bever and Norell, is known for its almost complete and well-preserved skull and large parts of the post-cranium (the remaining skeleton that adjoins the skull). The specific epithet altai points to the Altai Mountains .
Paleoecology
The sedimentary rocks at Nogon-Tsav are probably the same age as those of the Nemegt Formation . The age of this geological formation was never determined radiometrically , but the fauna documented in the fossil record suggests a deposition period during the Maastrichtian (about 72 to 66 million years ago), the last stage of the Cretaceous period.
The Maastrichtian period in Mongolia, as it is narrated in the Nemegt Formation and near Nogon-Tsav, is characterized by a humid climate - compared to the semi-arid environments in the older, underlying Barun-Goyot Formation and the Djadochta formation are preserved. The sediments of the Nemegt Formation contain the remains of flood plains, large rivers and paleo soils - but there were also periodic droughts. This environment provided space for a more diverse and generally larger dinosaur fauna than in earlier times. Kurzanov noticed that other theropods such as tarbosaurus , ornithomimosaurs and therizinosaurs were discovered in the same site; however, these remains have never been described in detail. If the Nogon Tsav fauna was similar to the fauna of the Nemegt Formation, there were also troodontid theropods, pachycephalosaurs , ankylosaurs and hadrosaurs . Sauropods from the group of titanosaurs were also a potential but very heavy prey for the predators of the Nemegt formation.
Individual evidence
- ^ Gregory S. Paul : The Princeton Field Guide To Dinosaurs. Princeton University Press, Princeton NJ et al. 2010, ISBN 978-0-691-13720-9 , p. 103, online .
- ↑ a b c d Stephen L. Brusatte, Thomas D. Carr, Gregory M. Erickson, Gabe S. Bever, Mark A. Norell : A long-snouted, multihorned tyrannosaurid from the Late Cretaceous of Mongolia . In: Proceedings of the National Academy of Sciences of the United States of America . Vol. 106, No. 41, 2009, pp. 17261-17266, doi : 10.1073 / pnas.0906911106 .
- ↑ a b c d e Сергей М. Курзанов: Новый позднемеловой карнозавр из Ногон-Цава, Монголия. In: Совместная советско-монгольская палеонтологическая экспедиция. Труды. Vol. 3, 1976, ISSN 0320-2305 , pp. 93-104.
- ^ Philip J. Currie : Theropods from the Cretaceous of Mongolia. In: Michael J. Benton , Mikhail A. Shishkin, David M. Unwin, Evgenii N. Kurochkin (Eds.): The age of dinosaurs in Russia and Mongolia. Cambridge University Press, Cambridge et al. 2003, ISBN 0-521-54582-X , pp. 434-455.
- ↑ a b c d e 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.
- ↑ a b c Jørn H. Hurum, Karol Sabath: Giant theropod dinosaurs from Asia and North America: Skulls of Tarbosaurus bataar and Tyrannosaurus rex compared . In: Acta Palaeontologica Polonica. Vol. 48, No. 2, 2003, ISSN 0567-7920 , pp. 161-190, (PDF file; 1.70 MB).
- ^ A b Philip J. Currie: Cranial anatomy of tyrannosaurids from the Late Cretaceous of Alberta . In: Acta Palaeontologica Polonica. Vol. 48, No. 2, 2003, pp. 191-226, (PDF; 1.8 MB).
- ↑ a b c Philip J. Currie, Jørn H. Hurum, Karol Sabath: Skull structure and evolution in tyrannosaurid dinosaurs . In: Acta Palaeontologica Polonica. Vol. 48, No. 2, 2003, pp. 227-234, (PDF; 137 kB).
- ↑ Thomas D. Carr, Thomas E. Williamson, David R. Schwimmer: A new genus and species of tyrannosauroid from the Late Cretaceous (middle Campanian) Demopolis Formation of Alabama. In: Journal of Vertebrate Paleontology. Vol. 25, No. 1, 2005, ISSN 0272-4634 , pp. 119-143, doi : 10.1671 / 0272-4634 (2005) 025 [0119: ANGASO] 2.0.CO; 2 .
- ↑ Евгений А. Малеев: Новый хищный динозавр из верхнего мела Монголии. In: Доклады Академии наук СССР. Vol. 104, No. 5, 1955, ISSN 0002-3264 , pp. 779-783 (In English: New carnivorous dinosaurs from the Upper Cretaceous of Mongolia. Online (PDF; 12.41 kB) ).
- ^ Philip J. Currie: Allometric growth in tyrannosaurids (Dinosauria: Theropoda) from the Upper Cretaceous of North America and Asia. In: Canadian Journal of Earth Sciences. Vol. 4, No. 4, 2003, ISSN 0008-4077 , pp. 651-665, doi : 10.1139 / e02-083 .
- ↑ Felix M. Gradstein, James G. Ogg, Alan G. Smith (eds.): A Geologic Time Scale 2004. Cambridge University Press, Cambridge et al. 2004, ISBN 0-521-78142-6 .
- ↑ a b Tomasz Jerzykiewicz, Dale Russell: Late Mesozoic stratigraphy and vertebrates of the Gobi Basin. In: Cretaceous Research. Vol. 12, No. 4, 1991, ISSN 0195-6671 , pp. 345-377, doi : 10.1016 / 0195-6671 (91) 90015-5 .
- ^ Halszka Osmólska : Nemegt Formation. In: Philip Currie, Kevin Padian : Encyclopedia of Dinosaurs. Academic Press, San Diego CA et al. 1997, ISBN 0-12-226810-5 , pp. 471-472.
Web links
![[1]](https://upload.wikimedia.org/wikipedia/commons/d/da/Alioramus_Life_Restoration.jpg){kind=link}
- Alioramus remotus ( Memento from January 25, 2007 in the Internet Archive ) at The Theropod Database (English)
- Skull image of Alioramus ( Memento from January 10, 2007 in the Internet Archive ) at The Grave Yard (English)