User:PaleoGeekSquared/sandbox3

PaleoGeekSquared/sandbox3 Temporal range: Late Jurassic, (Tithonian)
Speculative restoration and holotype tooth
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Family:	†Spinosauridae (?)
Genus:	†Ostafrikasaurus Buffetaut, 2012
Species:	†O. crassiserratus
Binomial name
†Ostafrikasaurus crassiserratus Buffetaut, 2012

Ostafrikasaurus is a genus of spinosaurid theropod dinosaur known from the Jurassic of Tendaguru, southeastern Tanzania. It contains a single species, Ostafrikasaurus crassiserratus.

Discovery and naming

Fossil excavation site during the Tendaguru expedition, 1912

During the time of the German colonial empire, the Müseum fur Naturkunde (Natural History Museum) of Berlin arranged an expedition in German East Africa (now Tanzania) that took place from 1909 to 1913; now considered by scientists as one of the largest expeditions in palaeontological history. The expedition led to the discovery of the first bones from the sauropod Giraffatitan brancai, which as at the time described as a new species of Brachiosaurus. Most of the excavations were situated in the southeastern Tendaguru Formation, a fossil-rich site part of the Mandawa Basin. Among the many dinosaur fossils retrieved from the dig sites was the holotype and only known specimen of Ostafrikasaurus, an isolated tooth catalogued as MB R 1084. It was originally referred to Labrosaurus? stechowi in 1920 by German palaeontologist Werner Janensch, the fossil was one among 230 specimens of theropod teeth brought back from the Tendaguru. A large and detailed monograph by Janensch published in 1925 assigned nine of these teeth to L.? stechowi and divided them into five morphotypes.

The genus Ostafrikasaurus was named by French palaeontologist Eric Buffetaut in a 2012 paper, based his 2007 reinterpretation of the fossil teeth; the type species is Ostafrikasaurus crassiserratus. The generic name is derived from the German name of the colony in which the holotype was found, Deutsch-Ostafrika, meaning "German East Africa". It is combined with the Greek σαῦρος/sauros, which means "lizard" or "reptile". The specific name is derived from the Latin crassus, meaning "thick"; and serratus, meaning "serrated", in reference to the morphology of the holotype tooth.

MB R 1084 was found in the Upper Dinosaur Member of the formation, it differs in several respects from the other eight teeth found in the Middle Dinosaur Member. Although in 2008 Buffetaut suggested that another isolated tooth (MB R 1091) from the Middle Dinosaur Member, may represent the same genus as MB R 1084, when naming Ostafrikasaurus, he did not refer it to the genus. The Upper Dinosaur Member of the Tendaguru Formation is composed mostly of siltstones, calcareous sandstones, and claystone beds. These rocks likely date back to the Tithonian stage of the Late Jurassic, approximately 152.1-145 million years ago. However, the precise chronological boundary between the Early Cretaceous and Late Jurassic of the Tendaguru Formation is still unclear.

Description

The holotype is a thick, fairly laterally flattened tooth about 46 mm (1.8 in) long. Erosion has rounded the tip of the tooth and the base is not fully preserved. The front cutting edge is curved while the back is nearly straight. The margins of the crown are well defined and feature small and rounded serrations from the tip to the base of the tooth, with two to four denticles every 1 mm (0.039 in). These serrations are relatively larger than in known spinosaurids. The enamel (outer layer) of the tooth has a series of ridges on its surface; ten on the lingual side, and four faint ones on the labial side. These striations do not reach the tip of the tooth and are at most separated by 1 mm (0.039 in) gaps, with a 3 mm (0.12 in) wide region on the lingual side that lacks ridges; a similarly-sized area on the labial side diminishes in width as it approaches the tip of the tooth.

Oliver Rauhut (2011) listed some of these differences: MB R 1084 has a much higher number of lingual ridges (up to ten) and presents four ridges and grooves on the labial side. Furthermore, some of the lingual ridges extend over almost the entire length of the crown, leaving only the apicalmost 5 mm of the crown smooth, whereas others are restricted to the basal part, being intercalated with ridges that extend further apically. Additionally, ridges are present over almost the entire mesial (front) threefifths of the crown, whereas the distal (back) two-fifths are devoid of any ornamentation. Mesially, the ridged area is slightly set off from the mesial carina by a slightly mesiodistally concave area. However, its general shape and serration density is very similar to the teeth from the Middle Dinosaur Marl, as all teeth have 10 denticles per 5 mm distally and 13 denticles per 5 mm mesially. Finally, Rauhut suggested that it is possible that this tooth represents the same taxon as the other teeth, or a closely related taxon.

Classification

Later the teeth were reassigned to ?Ceratosaurus stechowi, as Labrosaurus was found to be a junior synonym of Allosaurus. Oliver Rauhut suggested in his examination of Tendaguru theropods that Labrosaurus stechowi is a nomen dubium, and that these teeth are indeterminate, perhaps representing different taxa. In 2012 Buffetaut suggested that MB R 1084 tooth represents a new genus of Spinosauridae, and that it differs from other teeth previously referred to L.? stechowi. In 2012 Buffetaut assigned Ostafrikasaurus to the Spinosauridae, based on the fact that the tooth displays an enamel ornamentation that resembles many baryonychines including Baryonyx, but differs from all other known spinosaurids by the large size of the denticles borne by the carinae. Thus, Ostafrikasaurus, according to Buffetaut, represents the earliest currently known spinosaurid. The tooth suggests that the dental evolution of spinosaurids could have been characterised by reduction of the denticles.

Palaeoecology

Depiction of two Dicraeosaurus traversing tidal flats in the Tendaguru Formation

Ostafrikasaurus's habitat would have been subtropical to tropical, shifting between periodic rainfall and pronounced dry seasons. Three types of palaeoenvironments were present at the Tendaguru Formation, the first was a shallow water marine setting with lagoon-like conditions shielded behind shoals of ooid and siliciclastic rocks, evidently subjected to tides and storms. The second was a coastal environment of tidal flats, consisting of brackish water lakes, ponds, and fluvial channels. There was little plant-life in these environments for sauropods to feed on and most dinosaurs likely came to these areas only during droughts. The third and most inland habitat would have been dominated by conifer plants in a well-vegetated area, offering a large feeding ground for sauropod dinosaurs.

Extensive fossil finds have revealed that the Tendaguru was home to a diverse abundance of organisms. Invertebrates like bivalves, gastropods, oysters, echinoderms, arthropods, brachiopods, corals, and many microfauna are known from the deposits. Sauropod dinosaurs were prominent in the region, represented by Giraffatitan brancai, Dicraeosaurus hansemanni and D. sattleri, Australodocus bohetii, Janenschia robusta, Tornieria africana and Tendaguria tanzaniensis; they would have coexisted with low-browsing ornithischians like the ornithopod Dysalotosaurus lettowvorbecki, and the stegosaurian Kentrosaurus aethiopicus. Theropods besides Ostafrikasaurus included the carcharodontosaurid Veterupristisaurus milneri and the noasaurid Elaphrosaurus bambergi. Fragmentary material from the formation also indicates the presence of a basal ceratosaur and tetanuran, an unidentified abelisaur, as well as a possible abelisaurid, carcharodontosaurid, and megalosauroid.

Many other vertebrates contemporary with Ostafrikasaurus have been found at the formation, such as amphibians, lizards, bony and cartilaginous fish, various small mammals, the pterosaur Tendaguripterus, and the crocodile Bernissartia. Buffetaut (2012) stated that due to the presence of such a basal spinosaurid taxa in Africa, spinosaurids may have been widely distributed early in their evolutionary history.