THE GLOBAL SIGNIFICANCE OF THE ISLE QF WIGHT DINOSAURS
The dinosaurs of the Isle of Wight are of more than just local significance. The age of the fauna makes it unique, there being hardly any dinosaur faunas of exactly the same age anywhere in the world. Thus, the Isle of Wight fauna in combination with the dinosaurs from the Wealden Supergroup of Sussex, Surrey and Kent fill an important gap in our knowledge of dinosaur faunas and their evolution between the Late Jurassic and Mid Cretaceous. Furthermore, the similarity of Isle of Wight dinosaurs with slightly younger dinosaur faunas from Africa and North America demonstrates that faunal interchange between Europe and Africa, and between North America and Europe, probably via Greenland, was possible.
At least three Isle of Wight dinosaur genera have been reported from Africa. Taquet (1984) described two fragmentary snout tips that he regarded as being from spinosaurid theropods. Charig and Milner (1986, 1990, 1997) regarded these specimens as being indistinguishable from the snout tip of Baryonyx, and noted (Charig and Milner 1990) that Taquet agreed with their revised identification. This therefore supports the presence of Baryonyx in Africa. However, Taquet and Russell (1998) now contend that these African specimens are not from Baryonyx, but represent instead a new genus, Cristatusaurus. The validity of this taxon is dubious, as it is based on very inadequate material. The African baryonychid Suchomimus tenerensis from Niger also appears to be very closely related to Baryonyx (Sereno et al. 1998) and indeed it may be the case that Suchomimus is simply an adult Baryonyx as most of the differences appear to be size related (Angela Milner pers. com. 1999). .
Galton and Taquet (1982) described a species of Valdosaurus from the Mid Cretaceous of Niger that is very similar to the Wealden Group Valdosaurus canaliculatus. An iguanodontian tooth from the Lower Cretaceous of southern Tunisia was referred to Iguanodon by de Lapparent (1960), although Galton and Taquet (1982) consider it more probably from Ouranosaurus, an African iguanodontian that bore enormous neural spines along its back. .
There may be other dinosaurs in common between the Isle of Wight and African faunas. For example, among the sauropods, titanosaurians are represented in Africa and on the Isle of Wight, although the Isle of Wight material is so scrappy as to be of little palaeobiogeographic value. Brachiosaurids are well known from the Late Jurassic of Africa and a partial skeleton of a brachiosaurid from Barnes High, Isle of Wight, as well as other material, shows that the group was common to Europe, Africa and North America. .
Although there is an age difference of approximately 5-10 million years between the North African dinosaur faunas and those of the Isle of Wight, this is a relatively short time span in terms of dinosaur evolution. The similarity between the two faunas indicates that the Tethys Qcean between southern Europe and Africa presented no barrier to dinosaur dispersal or migration in Early to Mid Cretaceous times. .
On the North American continent Early Cretaceous dinosaur faunas from the Cedar Mountain Formation of Utah show some similarities with the Isle of Wight. The Cedar Mountain Formation crops out in east-central Utah and parts of Colorado. It spans a wide part of the Cretaceous, and the basal Yellow Cat Member is probably in part coeval with the Wealden Group of the Isle of Wight (Kirkland et al. 1998a, 1999). The Yellow Cat Member has yielded several dinosaurs also found in the Wealden Group of the Isle of Wight, including the sauropod Pleurocoelus and the ornithopod Iguanodon as well as the polacanthid ankylosaur Gastonia which is considered to be very closely related to Polacanthus. Kirkland et al. (1999) also report an undescribed allosauroid from the Cedar Mountain Formation, although whether or not this will prove to be similar to the Isle of Wight allosauroid Neovenator will only be determined by the discovery of more complete material. Although the Cedar Mountain Formation fauna is similar to the Isle of Wight fauna at the generic level, the two formations do not share any species in common. .
On other continents Early Cretaceous dinosaur faunas are so poorly known that it is difficult to make comparisons. In South America, dinosaur faunas from the (possibly) Albian Santana Formation have begun to be described. The Santana Formation spinosauroid Irritator challengeri demonstrates that spinosauroids were able to disperse between Africa and South America at this time, and so with dispersal between Africa and Europe possible, migration of dinosaurs between South America and Europe may also have been possible.
