Spinophorosaurus

Spinophorosaurus nigerensis, skeletal reconstruction ( from Remes et al., 2009)

• Niger, Agadez ( Irhazer Group)

• Spinophorosaurus nigerensis

Spinophorosaurus is a genus of sauropod dinosaur earlier. So far, two incomplete skeletons from the Middle Jurassic of Africa are known, which have been described so far in 2009 with the single species Spinophorosaurus nigerensis scientifically.

Spinophorosaurus is the best-known basal sauropod outside the Eusauropoda and thus understanding the early evolution of sauropods of great importance. This genus was distinguished as the related Shunosaurus by osteodermale weapons sting at the end of the tail.

Features

The type skeleton is estimated at a total length of 13 meters, but belonged to a subadult, so not fully grown, because some of the skull and vertebral sutures were not fused. The second skeleton was larger by about 13 %, with fully fused vertebrae seams indicate a full-grown animal.

The teeth are characterized by large denticles (small, serrated appendages ) with increased distance from each other. The spine consists of 13 cervical, 12 dorsal, 4 sacral, and 37 caudal vertebrae. The cervical vertebrae are prolonged moderate and show great lateral cavities at the centers ( Pleurocoele ). At the back vertebrae towards the Pleurocoele become weaker and weaker, while the vortex centers are relatively shorter for height. In the holotype skeleton of two closely related bone skin ( osteoderms ) have been found which are concave on the inside and facing up a sting. This 29 cm long structures were found in the pelvic region of the skeleton, were sitting in the living animal but probably at the rear end of the tail. Similar tail weapons are also found in the related Shunosaurus.

Autapomorphies, ie qualities enabling the species of related genera can distinguish, can be found at various elements of the skeleton. For example, the coracoid ( coracoid ) was kidney-shaped. Furthermore, the rear chevron bones overlapped and thus formed rod-like, horizontally extending structures.

Discoveries and naming

So far, two incomplete skeletons are known, the north of Aderbissinat ( Agadez region, Niger) have been discovered. The first skeleton ( holotype, specimen numbers GCP -CV - 4229 and NMB - 1699 -R ) consists of cranial bones ( skull, postorbital, squamosal, quadrate, pterygoid and Surangulare ) and an almost complete rest skeleton ( Postkranium ), in which only the sternum, the forearm, the missing finger and foot bones. While GCP -CV - 4229 is provisionally preserved in the Museo Paleontológico de Elche in Spain, NMB - 1699 -R is located at the Natural History Museum in Braunschweig. In the future, the entire skeleton at the Musee National d' Histoire Naturelle in Niamey (Niger ) will be given. Another Fund ( para-type NMB - 1698 -R ) - an incomplete skull and an incomplete Postkranium - shows not only bones that are already from the holotype skeleton known, but also other skeletal elements that are not received in the latter ( premaxilla, maxilla, lacrimal, Dental, Angular, dorsal ribs, humerus, and a single toe bone ).

Stratigraphy of the locality belongs to the base of the Irhazer group whose exact age is not known. Probably the finds from the Middle Jurassic ( Bajocian to Bathonian ) originate - an even older period of deposition of the sediments of the discovery site in the Lower Jurassic, however, can not be excluded. The skeletons were found 15 meters apart within a several meter thick layer of red siltstone.

The finds were scientifically described by researchers from Spain, Germany and the Niger in 2009. The genus name Spinophorosaurus (Latin spina - "thorn ", gr phoro - " bear ", sauros - " lizard" ) designation refers to the large, spike-like osteoderms, who probably sat as weapons at the end of the tail. The Artepiteth nigerensis has the Niger, from which the fossils.

Phylogeny and paleobiogeography

Spinophorosaurus considered as basal sauropod and sister taxon of Eusauropoda, which includes Shunosaurus and all modern sauropods with. With the discovery of Spinophorosaurus earlier ideas about evolution were earlier questioned sauropods and new hypotheses are. To confirm the researchers concluded that there was no monophyletic group of East Asian, mitteljurassischer sauropods, but that the common features of these East Asian species occur on much more basal sauropods. Instead, find greater anatomical differences between Spinophorosaurus and contemporary sauropod from the southern Gondwana, from which the researchers to a possible monophyletic group close südgondwanischer Eusauropoden. In this context, researchers disagree with the view that Sauropodenfaunen were uniform worldwide before the breakup of the supercontinent Pangaea.