Long-in-the-Tooth Dinosaur Offers Up New Wisdom

Creators of "Jurassic Park" take note: Tyrannosaurus rex was not alone.

Scientists have discovered remains of other enormous and fierce meat-eating dinosaurs that roamed the earth 70 million to 100 million years ago.

The most recent "unveiling" came this month from University of Chicago paleontologist Paul Sereno. Last summer in Morocco, he and his team discovered the skull of a Carcharodontosaurus - a "shark-toothed reptile from the Sahara" that lived 90 million years ago.

At 5-feet, four-inches long, the skull rivals in size the largest known skull of a Tyrannosaurus rex, which inhabited North America. Gabrielle Lyon, a Sereno team member, also discovered a partial skeleton of a new species, the smaller Deltadromeus, or "agile delta runner."

Not long after Mr. Sereno's toothy find in Morocco last summer, scientists in Argentina announced the discovery of the remains of Gigantosaurus - another gargantuan carnivore.

These meat-eating dinosaurs, or theropods, open wider the window on dinosaur evolution. "We want to see where all this fits in in the family tree," Sereno says.

Some 146 million years ago, the world's "supercontinent," called Pangaea, began drifting apart into different land masses, similar to the continents of today. Since Africa was closest to South America geographically at the time, many scientists assumed that Africa's dinosaurs were like South America's.

Not so. Sereno's work suggests that if anything, African dinosaurs had more in common with North American dinosaurs.

The new evidence shows that all these enormous predators evolved independently from one another during the Cretaceous period before extinction 65 million years ago.

Nevertheless, what's interesting is that these large theropods all evolved to be about 40 feet long and exceedingly similar in looks - despite being on different continents, says Mark Norell, a paleontologist at the American Museum of Natural History in New York. Tyrannosaurus rex was in North America; Tarbosaurus, T-rex's cousin, was in Asia; Gigantosaurus was in South America; and Carcharodontosaurus was in Africa.

"Of the major continent masses, we probably know the least amount about Africa," Mr. Norell says.

Sereno's team was the first to look intensively in Africa. Its discoveries are the most dramatic yet. Moreover, the Carcharodontosaurus skull solves a mystery.

In the late 1920s, fragmentary bones and some "wrinkled" teeth had been found in Egypt but they were destroyed in World War II.

When Sereno and his team worked to excavate the skull, they weren't sure what they had found. After initial analysis, they identified it as Carcharodontosaurus - the same theropod earlier scientists described based on fragments found 2,000 miles away.

"This was thrilling," says Sereno in a telephone interview. "We had discovered an animal that had ranged all across Africa."

Sereno concedes that many people want to know what was the biggest, most ferocious dinosaur. While Carcharodontosaurus probably weighed more than T-rex, other factors influence the comparison, Sereno says. Until they have a bigger sample and the understanding of the growth and variation, they can't judge with certainty.

The length of the Carcharodontosaurus skull is slightly longer than the largest-known T-rex skull, but the snout is strikingly narrower than T-rex's, Sereno says. Also, the brain cavity is about half the size, and the teeth - five inches long with wrinkles along the edge - are much more like blades.

Sereno says the discovery is a significant step forward for his mission: to understand the dinosaurian world on the southern continents.

"We're beginning to see outlines of what what existed. While we know North American and Asian fauna very well, we need to further sketch the [world] picture."