Content area
Full Text
Although increased continental isolation has been implicated as the driving force behind the differentiation of Cretaceous dinosaurian faunas (1), a coherent picture of dinosaurian biogeography during this period has not been possible because of the near absence of fossil evidence from key southern land masses such as Africa. With rare exceptions (2, 3), available information on Cretaceous dinosaurs from Africa is based on preliminary paleontological surveys in the Sahara (4), isolated or fragmentary bones and teeth (5), and a small fossil collection from Egypt that was destroyed during World War II (6, 7). We report here on the discovery of dinosaurs from Lower Cretaceous rocks in the southern Sahara Desert (Fig. 1) that impact on the understanding of late Mesozoic dinosaurian biogeography.(Fig. 1 omitted)
The fossils include the first relatively complete skeleton of a theropod dinosaur from the Cretaceous of Africa, Afrovenator abakensis, n. gen. n. sp. (8). The skull is low compared to that of other large-skulled predators such as Allosaurus (9). Maximum height at the orbit is less than one-third the skull length (Fig. 2A).(Fig. 2A omitted) Unlike Allosaurus and many other theropods, cranial crests and rugosities are poorly developed. The lacrimal crest, for example, has a low, rounded profile. As in many theropods, the lacrimal crest is hollowed by a pneumatic cavity. The maxilla has a slit-shaped promaxillary fenestra, a small, posteriorly positioned maxillary fenestra, and sockets for 14 blade-shaped teeth. The quadrate is tall with a dorsoventral length more than one-half the skull height at the orbit.
The skeleton is relatively gracile judging from the length and diameter of the long bones (Fig. 2C).(Fig. 2C omitted) Cervical vertebrae have deep pleurocoel cavities and articulate in an upward curve that elevates the skull above the dorsal column. The forelimb appears to be similar in length to that of Allosaurus but has different proportions within the limb. In Afrovenator the humerus is relatively longer, the carpus is flatter, the first metacarpal has stouter proportions, and the ungual on the third digit is particularly small (Fig. 2D and Table 1) (10).(Fig. 2D omitted) The pelvic girdle is similar in structure to that of Allosaurus (Fig. 2B).(Fig. 2B omitted) The ilium has a moderately developed supraacetabular crest and brevis fossa, the ischium has a trapezoidal...