U of C team again adds to knowledge of dinosaurs

The two dinosaurs, one of them a new species, are described in the cover article of the Friday, May 17, issue of Science and in the June issue of National Geographic. In addition to Lyon, team members included French and Moroccan paleontologists as well as Chicago graduate students Hans Larsson, Christian Sidor, Jeff Wilson and Paul Magwene.

"We really know very little about the kinds of dinosaurs that lived on Africa during the Cretaceous, the last period of the dinosaur era. Almost all of the evidence during this time comes from North America and Asia," said Sereno. "The new Moroccan fossils give us the first look at the kinds of predators that evolved on the isolated continent of Africa."

The new fossils solve a long-standing mystery surrounding fragmentary bones and some serrated teeth discovered in Egypt at the beginning of the century and later destroyed in World War II. The teeth in the huge skull found by Sereno's team matched the description of the lost Egyptian teeth, thereby indicating that the skull belonged to Carcharodontosaurus saharicus, or "shark-toothed reptile from the Sahara."

With a length of about five feet, four inches, the skull rivals in size the largest known skull of Tyrannosaurus rex, a dinosaur that lived 65 million to 70 million years ago in North America. The brain cavity of the newly found skull is well preserved and only half the volume of that known for T. rex, and only about onefifteenth the size of a human brain. In Africa, Carcharodontosaurus was the largest predator of its day and probably preyed on plant-eating sauropods. Sereno estimates the animal's length at 45 feet.

The second predator, discovered by Lyon and recovered by the team, has been identified as a new species from a partial skeleton. Named Deltadromeus agilis, or "agile delta runner," for its extraordinarily delicate, long limbs, this fleet-footed, meat-eating dinosaur is an early offshoot of the theropod line that on northern continents gave rise to Tyrannosaurus and the raptor Deinonychus. The reconstructed skeleton is greater than 25 feet in length. Lyon discovered Deltadromeus by spotting several of its toe bones embedded high in a rocky hillside.

The discoveries of Carcharodontosaurus and Deltadromeus shed light on the final chapter of dinosaur evolution in Africa. The earliest dinosaurs looked remarkably alike worldwide. But by the time Carcharodontosaurus and Deltadromeus appeared, some 90 million years ago, the earth's land had become a patchwork of isolated island continents. The team's discoveries suggest that, once isolated, the dinosaurs on Africa and other continents embarked on divergent evolutionary paths.

Fossil crocodile teeth, turtle shell, crayfish, petrified wood and dinosaur footprints found near the sites of the skull and skeleton provide evidence that today's scorched Sahara once was a vast flood plain laced with rivers edged by coniferous trees. Crocodiles and turtles swam the rivers, and predatory dinosaurs like Deltadromeus ran through the mud, leaving dozens of three-toed tracks now fossilized in the sediment.

The remains of Carcharodontosaurus and Deltadromeus were found in the Kem Kem region of Morocco's Sahara. Scaling the region's slopes in 120-degree heat to uncover the bones, some members of Sereno's team lost more than 20 pounds each in the first month of the expedition. Rubble-strewn inclines tore up their boots, which had to be patched with strips of rubber from truck tires.

"Between the extreme heat and the steep slopes we climbed, this was one of the most physically demanding expeditions I have ever been on," said Sereno. "The area is also frequented by local and foreign fossil-collectors whose aim is to sell the bones and teeth they find. Often broken in haste, and taken out of context, these fossils are rarely seen by scientists. It took us two long, hard months of desert climbing to find the fossils that would show what these animals might have looked like and place them in the dinosaur family tree."

The expedition and research were sponsored by the David and Lucile Packard Foundation, the Eppley Foundation for Research and the National Geographic Society.

-- Diana Steele