Nigersaurus
| Nigersaurus | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
![Outline reconstruction i. W. on the basis of the preserved bones of four individuals [1]](https://de.wikipedia.org/wiki/Datei:Nigersaurus_taqueti_skeleton.png)
Outline reconstruction i. W. on the basis of the preserved bones of four individuals |
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| Temporal occurrence | ||||||||||||
| Lower Cretaceous (late Aptian ) | ||||||||||||
| 123 to 112.9 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Nigersaurus | ||||||||||||
| Sereno et al. , 1999 |
Nigersaurus is a genus of sauropod dinosaurs from the Rebbachisauridae group thatlived in Africaduring the Lower Cretaceous (late Aptian ). The approximately 10-meter-long herbivore heard how the much larger Diplodocus to the diplodocoidea . So far only the type species Nigersaurus taqueti has been scientifically described (Sereno et al. , 1999).
discovery
Nigersaurus fossils were discovered mainly by two expeditions in 1997 and 2000 in the Gadoufaoua site in the Sahara desert ( Republic of Niger ). Geologically speaking, Gadoufaoua belongs to the Elrhaz Formation and is located on the eastern edge of the Ténéré desert, it is particularly known as the place where the giant crocodile Sarcosuchus , the spinosaurid Suchomimus and the bird basin dinosaur Ouranosaurus were found .
The holotype material (MNN GDF512) consists of a fragmentary skull and partially connected neck elements that were discovered in the 1997 expedition over an area of only one square meter. Among other things, most of the top of the skull is preserved, and the brain skull (neurocranium) is intact. Other bones found in the immediate vicinity include the shoulder blade (scapula), front and rear legs. At other locations in the Gadoufaoua region, the expedition was able to recover further partial skeletons and isolated bones. A partial skeleton, which was described by Philippe Taquet as early as 1976 , very probably also belongs to this species.
The 2000 expedition discovered another partial skeleton (MNN GAD517). In 2005 and 2007 important publications on this genre followed ;; a CT scan of the skull was also used. With the research of the Nigersaurus , the skull anatomy of a Rebbachisaurid could be documented for the first time, and a sauropod brain could be completely reconstructed for the first time.
A skeleton can be seen in the National Geographic Museum in Washington .
features
Nigersaurus is one of the most unusual sauropods that have ever been discovered - especially considering the extremely light skull. It shows extreme adaptations for a herbivorous dinosaur.
skull
Overall, the skull is extremely light - so the connecting bones that connect the snout to the back of the head are rarely thicker than two millimeters; the area of the cross-section of these bones is only about one square centimeter in total.
The two lower jaws are L-shaped when viewed from above and form a very wide, box-shaped set of teeth that contain straight rows of teeth perpendicular to the longitudinal shaft of the lower jaw - a unique feature among dinosaurs. The width of the muzzle at its foremost end slightly exceeds the total length of the lower jaw.
The upper and lower jaws have tooth batteries that are deeply embedded in the maxillary, premaxillary and dental. There were up to 10 replacement teeth under each of the over 100 active teeth; the skull had over 500 teeth in total. They acted like scissors cutting off vegetation. The teeth wore out quickly - no other dinosaur is known to have a higher rate of wear. The dental batteries ensured a continuous change of teeth , according to Sereno, a tooth was regrowed about every month. In any case, Nigersaurus did not have any of the special adaptations that have been demonstrated in other dinosaurs with dental batteries; the Ceratopia or the Hadrosauridae , for example, had a solid snout, larger attachments for the adduction muscles, and much more
Unique among all known Sauropodomorpha are some features related to the skull openings; there are five additional windows, especially in the lower jaw, while the supratemporal window is closed.
The brain case is exceptionally well preserved - only the parietal and supraoccipital bones were lost and had to be reconstructed. The brain was reconstructed using computed tomography and silicone casts; For the first time, the results offer a closer look at the front part of a sauropod brain , including the cerebrum and olfactory bulb . The cerebrum is convex and, like many other dinosaurs, makes up 30% of the total brain . The olfactory bulbs are small, which indicates a rather poor sense of smell. Overall, the brain is estimated to be 53.4 cm³, which is very small compared to non-sauropod dinosaurs. Nigersaurus , for example, has less than a third of the brain mass of the similarly sized theropod Carcharodontosaurus .
Postcranial skeleton
With an average length of nine meters and a femur length of about one meter, Nigersaurus was a smaller sauropod. The neck is short compared to other sauropods, the 13 cervical vertebrae are only 130% of the length of the spinal column. A short neck and a smaller size characterize most Rebbachisauriden and Dicraeosauriden , which are in contrast to the large, long-necked Diplodociden . However , it is not clear whether these characteristics of the Diplodocidae are derived characteristics of this family, or whether the common characteristics of the Dicraeosauridae and the Rebbachisauridae have developed convergent .
Overall, the skeleton is extremely light; the dorsal and cervical vertebrae are deeply hollowed out and consist only of thin plates of bone. “The vertebrae are as thin as paper - it's hard to imagine how they were able to cope with the daily stress. But we know they were up to the challenge, ” said co-author Jeffrey A. Wilson , assistant professor at the University of Michigan . The shoulder and pelvic girdles also consist of thin, only a few millimeters thick, bone sheets; only the caudal vertebrae and the limbs were less specialized.
Paleobiology
Head posture and diet
Investigations of the inner ear have shown that the head was usually directed 67 degrees downwards, almost twice as much as Diplodocus' (37 degrees). In contrast, the prosauropod Massospondylus , a basal sauropodomorph, had its head tilted 15% upwards when it was in a neutral position.
Like all Diplodocoidea, Nigersaurus ate vegetation close to the ground, the head was usually not far from the ground. This way of eating is also supported by the width of the snout, which increases the amount of food that can be ingested in one bite on flat surfaces.
It is not possible to say exactly which special plants the diplodocoids ate, as only a few stomach contents and corresponding petrified feces ( coprolites ) were found. In addition, the florets are difficult to reconstruct and the teeth show hardly any adaptations to certain plants. In the case of Nigersaurus , however, due to the very weak chewing muscles, one can assume a soft plant food, which is why horsetail and ferns are considered. Since it did not appear until the end of the late Cretaceous period, grass is ruled out as a food source.
Systematics
The Rebbachisauridae, together with the Diplodocidae and the Dicraeosauridae , are classified within the Diplodocoidea. Within the Rebbachisauridae, the closest relative of the Nigersaurus is an animal from Spain, which was described in 2003 but has not yet been named. Sereno et al. (2007) hypothesized that the unknown original form of the Diplodocoidea, analogous to the Dicraeosauridae and the Rebbachisauridae, was rather small and had a short neck. This would mean that the long neck and large body dimensions of the Diplodocidae, as known from Apatosaurus and Diplodocus , are derived features. The Diplodocidae would be the exception, while it was previously assumed that their physique was characteristic of the Diplodocoidae.
literature
- Paul C. Sereno , Allison L. Beck, Didier B. Dutheil, Hans CE Larsson, Gabrielle H. Lyon, Bourahima Moussa, Rudyard W. Sadleir, Christian A. Sidor, David J. Varricchio, Gregory P. Wilson, Jeffrey A. Wilson: Cretaceous Sauropods from the Sahara and the Uneven Rate of Skeletal Evolution Among Dinosaurs. In: Science . Vol. 286, No. 5443, 1999, pp. 1342-1347, doi : 10.1126 / science.286.5443.1342 .
Web links
- Paul Sereno, Jeffrey A. Wilson, LA Witmer (recte: Lawrence M. Witmer ), John A. Whitlock, Abdoulaye Maga, Oumarou Ide, Timothy B. Rowe : Nigersaurus taqueti (On-line), Digital Morphology. Accessed: August 16, 2014.
Individual evidence
- ↑ a b c d e f g h i j k l m n o p q r Paul C. Sereno, Jeffrey A. Wilson, Lawrence M. Witmer, John A. Whitlock, Abdoulaye Maga, Oumarou Ide, Timothy A. Rowe: Structural Extremes in a Cretaceous Dinosaur. In: PLOS ONE . Vol. 2, No. 11, 2007, e1230, doi : 10.1371 / journal.pone.0001230 .
- ^ Gregory S. Paul : The Princeton Field Guide To Dinosaurs. Princeton University Press, Princeton NJ et al. 2010, ISBN 978-0-691-13720-9 , pp. 185-186, online .
- ↑ a b c d Paul C. Sereno, Jeffrey A. Wilson: Structure and Evolution of a Sauropod Tooth Battery. In: Kristina Curry A. Rogers, Jeffrey A. Wilson (Eds.): The Sauropods. Evolution and Paleobiology. University of California Press, Berkeley CA et al. 2005, ISBN 0-520-24623-3 , pp. 157-177, doi : 10.1525 / california / 9780520246232.003.0006 .
- ↑ a b Paul C. Sereno, Allison L. Beck, Didier B. Dutheil, Hans CE Larsson, Gabrielle H. Lyon, Bourahima Moussa, Rudyard W. Sadleir, Christian A. Sidor, David J. Varricchio, Gregory P. Wilson, Jeffrey A. Wilson: Cretaceous Sauropods from the Sahara and the Uneven Rate of Skeletal Evolution Among Dinosaurs. In: Science. Vol. 286, No. 5443, 1999, pp. 1342-1347, doi : 10.1126 / science.286.5443.1342 .
- ↑ Netzeitung ( Memento from November 11, 2013 in the Internet Archive )
- ^ Paul Upchurch , Paul M. Barrett , Peter Dodson : Sauropoda. 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. 259-324, here p. 304.
- ↑ mirror