Ostafrikasaurus

during the Tendaguru expedition, 1910 During the time of the German colonial empire, the Museum für Naturkunde (Natural History Museum) of Berlin arranged an expedition in German East Africa (now Tanzania) that took place from 1909 to 1912, and is now regarded by scientists as one of the largest expeditions in palaeontological history. Most of the excavations were situated in the southeastern Tendaguru Formation, a fossil-rich site part of the Mandawa Basin dated to the Late Jurassic period. Among the many dinosaur fossils retrieved from the dig sites were 230 specimens of theropod teeth. It was originally attributed to the species Labrosaurus? stechowi in 1920 by German palaeontologist Werner Janensch, based on comparable ornamentation to a tooth described as Labrosaurus sulcatus by Othniel Charles Marsh. A detailed monograph by Janensch published in 1925 assigned MB R 1084, as well as eight teeth from the Middle Dinosaur Member to L.? stechowi and divided them into five morphotypes (from a to e). In 2000, American palaeontologists James Madsen and Samuel Welles referred the L.? stechowi teeth to Ceratosaurus sp. (of uncertain species), because they resembled teeth from the premaxilla and dentary jaw bones of Ceratosaurus, a theropod from the North American Morrison Formation. This analysis was maintained by French palaeontologist Eric Buffetaut, who examined the teeth that year, and in a 2008 paper referred specimen MB R 1084 to the Spinosauridae. Bufetaut found that this specimen differed from other teeth previously referred to L.? stechowi, and that another isolated tooth (MB R 1091) from the Middle Dinosaur Member might represent the same animal. He also questioned Janensch's provisional assignment of the teeth to the dubious genus Labrosaurus, which was based on scant remains from the Morrison Formation that were later attributed to Allosaurus. Furthermore, Buffetaut noted that the L. sulcatus tooth illustrated by Marsh is now regarded as belonging to Ceratosaurus''. as Ostafrikasaurus teeth are now believed to have represented Ceratosaurus (pictured) or a similar animal In 2011, German palaeontologist Oliver Rauhut considered the Middle Dinosaur Member teeth ascribed to L.? stechowi as lacking diagnostic characters (unique derived traits), concurring that the species is a dubious name. Rauhut noted that they can still be differentiated from other theropod teeth from the Tendaguru Formation, based on their slight recurvature and sideways flattening of the tooth crown, and broad ridges on the lingual flank (which faced the inside of the mouth). In a 2012 paper, Buffetaut used MB R 1084 as the holotype specimen for the new genus and species Ostafrikasaurus crassiserratus, describing it as an early spinosaurid theropod. Its generic name is derived from the German name of the colony in which the fossils were found, Deutsch-Ostafrika, meaning "German East Africa", combined with the Greek (''), meaning "lizard" or "reptile". The specific name comes from the Latin , meaning "thick"; and ,'' meaning "serrated", in reference to the large serrations of its teeth. Due to similarities with MB R 1084, Buffetaut assigned MB R 1091 from the Middle Dinosaur Member to the same species. Both teeth have a curved front carina, no side to side curvature, and a comparable shape in cross section. Their main differences include MB R 1091 having five lengthwise ridges on its lingual side compared to MB R 1084's ten, the ridges on the former being less extensive. MB R 1091 also had less wrinkled tooth enamel. Buffetaut notes that these differences could be explained by individual variation within the taxon, but since both teeth originated from different members of the Tendaguru Formation, the referral is only tentative. Another study published in the same year argued that the fragmentary tooth taxa Ostafrikasaurus and Siamosaurus should be regarded as nomina dubia. ==Description==

The body size of Ostafrikasaurus cannot be reliably calculated to due the highly incomplete nature of current material. The holotype tooth is thick, somewhat flattened sideways, and in length from top to bottom. Its tip has been rounded by erosion and the base is not fully preserved. The tooth crown has well-defined carinae (cutting edges), with the front carina being curved and the back carina almost straight. There is only mild side-to-side curvature. Both carinae are serrated, with rounded denticles perpendicular to the edge of the tooth. The serrations have no inderdenticle sulci, or grooves, in between them. They line the front carina from the base to its tip, and probably also did on the back carina, whose base has been largely eroded. Towards the tip of the tooth, these serrations are very worn down (especially on the front carina). On the front carina, there are two denticles per mm (0.04 in) near the tip of the tooth, and three to four per mm (0.04 in) as the denticles shrink towards the base of the crown. There are two denticles per mm (0.04 in) all along the back carina. The serrations are notably larger than in all other known spinosaurids. The enamel (outermost layer) of the tooth bears a series of ridges on its surface – 10 on the lingual side, and four fainter, less extensive ones on the labial side. The gaps between ridges are wide at most. None of the ridges on either side reach the tip of the crown. There is a wide region at the front of the tooth on both sides that lacks ridges; a similar area on the rear of the tooth side diminishes in width, from as it approaches the tip of the crown. On both sides of the tooth, between the ridges and ridge-less parts of the teeth, the enamel surface is finely wrinkled. ==Classification==

'', a spinosaurid from the Early Cretaceous of western Europe Spinosaurids are usually separated into two subfamilies: Baryonychinae and Spinosaurinae. In regards to dental traits, baryonychines are characterized by slightly curved, finely-serrated teeth with more oval cross sections, while spinosaurine teeth are straight, bear highly reduced or completely absent serrations, have more circular cross sections, and bear prominent flutes (lengthwise grooves) on their enamel. In 2007, Fowler interpreted the L.? stechowi'' teeth as representing a possible primitive baryonychine or ancestral form to baryonychines, since they share features, such as tightly packed serrations, stout shape, marginally flattened tooth crowns, and ridges on their lingual face, typically associated with that clade. The naming and distinction of new dinosaurs based solely on teeth has been frequently considered problematic by palaeontologists, such as with the debated identity of the Asian genus Siamosaurus.'''' Buffetaut stated that with thorough comparison and analysis of morphological features such as ornamentation, theropod teeth can be sufficiently diagnostic enough to raise new taxa. However, this specimen has been noted by other researchers to possess many non-spinosaurid features, these researchers instead favoring a megalosaurid identification. == Palaeobiology ==

Though no skull material has been discovered for Ostafrikasaurus, it is known that spinosaurid skulls resembled those of crocodiles; they were long, low, narrow and expanded at their front ends into a terminal rosette-like shape, with a robust secondary palate on the roof of the mouth that made them more resistant to stress and bending. In contrast, the primitive and typical condition for theropods was a tall, broader and wedge-like snout with a less developed secondary palate. The skull adaptations of spinosaurids converged with those of crocodilians; early members of the latter group had skulls similar to typical non-avian (or non-bird) theropods, later developing elongated snouts, conical teeth, and secondary palates. These adaptations may have been the result of a dietary change from terrestrial prey to fish. In 2012, Buffetaut suggested that the reduction of serrations on spinosaurid teeth illustrated by Ostafrikasaurus may represent a transition during this shift in diet. == Palaeoenvironment and palaeobiogeography ==

'' traversing tidal flats in the Tendaguru Formation|alt= 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 Period, approximately 152.1 to 145 million years ago. However, the precise chronological boundary between the Early Cretaceous and Late Jurassic of the Tendaguru Formation is still unclear. The Tendaguru Formation was home to a diverse abundance of organisms. Invertebrates like bivalves, gastropods, oysters, echinoderms, arthropods, brachiopods, corals, and many microfauna, including ostracods, foraminifera, charophytes, and palynomorphs are known from the deposits. 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 fossils also indicate the presence of a basal ceratosaurid (Ceratosaurus? stechowi) and tetanuran, an unidentified abelisauroid, as well as a possible abelisaurid, carcharodontosaurid, and megalosauroid. lissamphibian amphibians, paramacellodid lizards, and various small mammals, Allostaffia aenigmatica, Tendagurodon janenschi, Tendagurutherium dietrichi'', and multiple unidentified symmetrodonts. The flora of the Tendaguru Formation was equally varied, with vegetation consisting of araucarians, cypresses, cycads, yews, Cheirolepidiaceae, Ginkgoaceae, and Prasinophyta. There were also dinoflagellate and Zygnemataceae algae, as well as numerous pollen and spore taxa. In 2007, Fowler noted that a baryonychine identification for the L.? stechowi teeth would suit biogeographical models proposed at the time for spinosaur evolution and distribution, which assumed an origin for the group in the southern supercontinent Gondwana, with later spread and diversification in Europe. and Ronan Allain and colleagues in 2012, the latter having suggested that such a spread may have occurred earlier across Pangaea, prior to its breakup starting in the Late Jurassic. The palaeobiogeography of spinosaurids remains poorly understood, and was likely very complex, given discoveries in Asia and possibly Australia, as well as the resemblance between some European and Asian taxa. ==References==