AS PAUL SERENO SCANNED THE VALley in southeast Morocco last July, he spied a reddish patch high on a cliff. Its color left no doubt that it was sandstone, which preserves fossils as well as anything short of a museum case. The University of Chicago paleontologist began climbing. Near the top, he came upon a yellowed, grapefruit-size bone fragment. Sereno identified it as part of the skull of a huge carnivorous dinosaur, one that towered atop the African food chain 90 million years ago when the region was cut by rivers and dotted with conifers. Last week Sereno announced that the 5-foot, 4-inch-long skull of Carcharodontosaurus saharicus ("shark-toothed reptile from the Sahara") was as large as or larger than skulls of Tyrannosaurus rex, until recently the undisputed king of terrestrial carnivores.
Carcharodontosaurus, an estimated 45 feet long and eight tons in weight, is only the latest challenger for the size crown. Last September, Argentine paleontologists announced the discovery of Giganotosaurus, also heavier and larger-skulled than T. rex (though rex was apparently taller and longer-limbed than either upstart). Bits of Carcharodontosaurus had been known since 1927, but until now scientists didn't realize what they had. As notable as its size is its similarity to Giganotosaurus, Sereno and his colleagues report in the journal Science. Ancestors of the behemoths apparently dispersed throughout the Americas and Africa. And now it seems that their far-flung prog- eny never lost their family resemblance.