Nigersaurus

Outline reconstruction in Westphalia on the basis of the preserved bones of four individuals

• Niger ( Elrhaz Formation)

Nigersaurus is a genus of sauropod dinosaur from the group of Rebbachisauridae, during the Lower Cretaceous ( Aptian late ) lived in Africa. The approximately 10 meter long herbivore as part of the much larger Diplodocus to the Diplodocoidea. So far, only the type species Nigersaurus taqueti been scientifically described ( Sereno et al., 1999).

• 3.1 head posture and nutrition

Discovery

Fossils of Nigersaurus were discovered mainly of two expeditions in 1997 and 2000 in the archaeological site Gadoufaoua in the Sahara Desert (Republic of Niger). Gadoufaoua belongs geologically to Elrhaz lineup and lies on the eastern edge of the Ténéré Desert, it is particularly well known as the site where the giant crocodile Sarcosuchus, the Spinosauriden Suchomimus and the bird Beck dinosaur Ouranosaurus.

The holotype material ( MNN GDF512 ) consists of a fragmentary skull and neck of partially connected elements that have been discovered in the expedition in 1997 to an area of ​​only one square meter. Among other things, the majority of the skullcap is obtained, and the braincase ( neurocranium ) is intact. Further, found in the vicinity of bone, close shoulder blade (scapula ), front and hind legs with a. For other locations in the region Gadoufaoua the expedition more partial skeletons and isolated bones could entail. A partial skeleton, which was already described in 1976 by Philippe Taquet, also belongs very probably to this species.

The expedition in 2000 discovered another partial skeleton ( MNN GAD517 ). In the years 2005 and 2007 was followed by important publications on this genus; ; whereby a CT scan of the head was used. With the exploration of the Nigersaurus first time the cranial anatomy of a Rebbachisauriden could be documented, more could be completely reconstructed for the first time a sauropod brain.

A skeleton can be seen in the National Geographic Museum in Washington.

Features

Nigersaurus is one of the most unusual sauropods ever discovered - particularly in view of the extremely lightweight skull. He shows extreme adaptations for a herbivorous dinosaur.

Overall, the skull is extremely easy to build - so the connecting bones that connect the nose to the back of the head, rarely thicker than two millimeters; the area of the cross section of the bone is only around one square centimeter.

The two lower jaws are viewed from above, L -shaped and form a very broad, box-shaped teeth, the straight, transverse to the longitudinal shaft of the lower jaw standing rows of teeth contains - a unique feature among dinosaurs. The width of the nose at its forward end slightly longer than the total length of the mandible.

Maxilla as the mandible have tooth batteries, which are deeply embedded in the maxilla, the Premaxillare and the Dental. So were under each of the more than 100 active teeth up to 10 permanent teeth, the skull had a total of about 500 teeth. The teeth had the sections vegetation like scissors. The teeth wore out quickly from there - no other dinosaur greater Abnutzrate is known. The tooth batteries made ​​for a continuous change of teeth, according to Sereno about every month grew by a tooth. Anyway Nigersaurus had none of the special adaptations that have been demonstrated in other dinosaurs with tooth batteries; the Ceratopia or Hadrosauridae for example, had a solid nose, large batches for the adductor muscles, etc.

Unique among all known Sauropodomorpha are some related to the skull openings characteristics; so there are five additional windows, especially in the lower jaw, while the Supra pace Ralf Rochester is closed.

The brain case is exceptionally well received - only the parietal and Supraoccipitalknochen were lost and had to be reconstructed. The brain was reconstructed by computer tomography and silicone casts; the results provide a closer look at the front part of Sauropodenhirns, including cerebrum and olfactory bulb first. The cerebrum is convex and smooth, as with many other dinosaurs, 30 % of the total brain out. The olfactory bulbs are small, which indicates a rather poorer sense of smell. Overall, the brain is estimated at a size of 53.4 cm ³, which, however, compared with non- sauropod dinosaurs, is very small. Nigersaurus for example, has less than one third of the brain mass of similarly sized theropod Carcharodontosaurus.

Postcraniales skeleton

With an average length of nine meters and a femur length of about one meter Nigersaurus was a small sauropod. The neck is short compared with other sauropods, the 13 cervical vertebrae have only 130 % of the length of the back spine. A short neck and a smaller size distinguish the most Rebbachisauriden and Dicraeosauriden that are so unlike the large, long-necked diplodocids. Whether these features of diplodocids are derived characteristics of this family, or whether the common characteristics of Dicraeosauridae and Rebbachisauridae have developed convergent, but it is not clear.

The skeleton is overall extremely light, so the back and neck vertebrae are severely eroded and only consist of thin plates of bone. " The vertebrae are so paper thin - you can hardly imagine how they had grown daily stresses. But we know that they were up to the task well, "said co-author Jeffrey Wilson, assistant professor at the University of Michigan. Also, the shoulder and pelvic girdles are made of thin, only a few millimeters thick, bone leaves; only the vertebrae of the tail and limbs were less specialized.

Paleobiology

Head posture and nutrition

Studies of the inner ear have shown that the head was usually directed at 67 degrees down; about twice as much as in Diplodocus (37 degrees). In contrast, the Prosauropode Massospondylus, a basal Sauropodomorphe, with a neutral attitude towards the head tilted or by 15% upwards.

Like all Diplodocoidea ate also Nigersaurus ground vegetation, the head was usually not far from the ground. This way feeding is also supported by the very broad snout, which, increases the amount of food that can be included with a bite on straight surfaces.

Which plants have eaten exactly Diplodocoiden, you can not say exactly, because few stomach contents and the appropriate fossilized feces ( coprolites ) have been found. In addition, the floras can be reconstructed accordingly difficult, and the teeth show little adjustments to certain plants. In Nigersaurus it can be considered due to the weak muscles of mastication of a soft plant food, which is why horsetails and ferns are considered. Grass separates, as it only appears at the end of the Late Cretaceous Period, as a food source.

System

The Rebbachisauridae will, filed together with the Diplodocidae and Dicraeosauridae within the Diplodocoidea. Within the Rebbachisauridae regarded as the closest relative of the Nigersaurus a described already in 2003, but still unnamed animal from Spain. Sereno et al. (2007) hypothesized that unknown initial form of Diplodocoidea is analogous to the Dicraeosauridae and Rebbachisauridae, rather small and have a short neck. This would mean that it is the long neck and large body size of Diplodocidae, as we know from Apatosaurus and Diplodocus order is derived characteristics. The Diplodocidae would thus be the exception, whereas before it ran out, her physique would be characteristic of the Diplodocoidae.