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The tooth of Ostrafrikasaurus as seen from the front (A), tongue side (B), back (c) and cheek side (d). From Buffetaut, 2011.

There’s a lot we don’t know about spinosaurs. Even though a few of these croc-snouted animals are known from mostly complete skeletons—including Baryonyx and Suchomimus—many spinosaurs are known from only sparse bits and pieces. The large spinosaur Oxalaia from the Cretaceous rock of Brazil is known from two skull fragments, and only a few elements have been found from the newly announced Ichthyovenator. We know even less about another recently proposed spinosaur. Called Ostafrikasaurus, this dinosaur is represented by a pair of teeth.

Paleontologist Eric Buffetaut described the dinosaur teeth in the journal Oryctos. They were found a century ago by the German fossil expeditions to Tanzania. During that time, the field team collected more than 230 teeth attributable to Late Jurassic theropod dinosaurs, predators that lived among sauropods and stegosaurs around 150 million years ago. Determining exactly which dinosaurs these dental tidbits belonged to has been a persistent problem. Mammal teeth, with their various cusps and troughs, are often distinctive enough to identify genera and species, but isolated dinosaur teeth are not usually so informative. Many dinosaur species named from teeth alone have turned out to be synonyms of dinosaurs known from better material. Unless you have a detailed knowledge of the dinosaurs that lived in a particular area at a given time, attributing isolated teeth to particular dinosaurs is a risky proposition. Anatomical context is extremely important in these situations.

No surprise, then, that the teeth Buffetaut described have had a complicated history. German paleontologist Werner Janensch, who did much of the initial descriptive work on the Jurassic dinosaurs of Tanzania, thought that the serrated, ridged and slightly curved teeth probably belonged to a dinosaur O.C. Marsh named from the Jurassic of North America, “Labrosaurus.” (“Labrosaurus” is now considered a synonym of Allosaurus.) More recently, in 2000, paleontologists James Madsen and Samuel Welles suggested that the teeth belonged to a form of Ceratosaurus, a highly ornamented theropod typically found in the Late Jurassic rock of western North America. And in 2008, paleontologist Denver Fowler mentioned that these peculiar teeth from Tanzania might hint at a connection between ceratosaurs and spinosaurs. With this in mind, Buffetaut reexamined the strange teeth and concluded that they represent a hitherto unknown form of early spinosaur.

Buffetaut singled out two possible spinosaur teeth—specimens designated MB.R.1084 and MB.R.1091. Both of these teeth have relatively coarse serrations and a number of prominent vertical ridges along both sides of the teeth, with more on the tongue side than the cheek side. Overall, they look similar to the teeth of Baryonyx, and so Buffetaut created a new genus and species of dinosaur for the two teeth: Ostafrikasaurus crassiserratus.

If Ostafrikasaurus is a spinosaur, it would be the earliest known and could help elucidate what these dinosaurs were like before they became fish-catching specialists. But there’s too little material to be sure. The Ostrafrikasaurus teeth look similar to spinosaur teeth, but as previously recognized by other paleontologists, they also resemble ceratosaur teeth. We need a nice skull set with Ostrafrikasaurus-like teeth to determine what this dinosaur actually was. The same is true of a large claw found in the Late Jurassic strata of North America, currently attributed to Torvosaurus, that has been highlighted as possible evidence of a spinosaur. There may have been spinosaurs in North America, and their history might have stretched back 150 million years to the time of Apatosaurus, but definitive proof remains elusive. Until adequate fossil evidence turns up, the idea of Late Jurassic spinosaurs will be left hanging.

References:

Buffetaut, E. 2011. An early spinosaurid dinosaur from the Late Jurassic of Tendaguru (Tanzania) and the evolution of the spinosaurid dentition. Oryctos. 10, 1-8