BOSTON, MASS.--What's next for dinosaur expert Paul C. Sereno, and what can we learn from his studies of large fossils found in Africa?
Sereno's ongoing field work in Africa has yielded a menagerie of new dinosaurs. These discoveries have included the giant predator, Carcharodontosaurus, which rivaled Tyrannosaurus in size. Another find was the fleet-footed meat-eater, Deltadromeus, that has no close counterpart on other continents; and the spinosaur, Suchomimus. Giant long-necked plant-eaters, found in a communal death site, included the 60-foot long Jobaria.
The latest discoveries by Sereno, a paleontologist at the University of Chicago, have included the 40-foot long crocodilian, Sarcosuchus--otherwise known as "super-croc"--and several smaller relatives, such as a tiny dwarf croc. Other recent finds included Africa's first small predatory dinosaur, and a very unusual armored plant-eater.
"Such finds are rapidly filling in Africa's dinosaur world during its phase of isolation during the Cretaceous," Sereno noted.
Discoveries of the past decade have transformed the fossil record of dinosaurs, he added--from their first appearance in the middle Triassic, to their final radiations at the end of the Cretaceous. "The fossiliferous sequence of middle to late Triassic beds in northwestern Argentina provides a very complete look at the earliest dinosaurs and the timing of the dinosaurian radiation," he said.
Primarily on the basis of his fossil evidence, which includes very complete skeletons of the early theropods, Eoraptor and Herrerasaurus, Sereno proposes that the initial radiation of dinosaurs significantly preceded their global dominance in diversity and abundance.
Fossil discoveries help establish a global picture of dinosaur evolution, and, they underscore the role of large-scale extinction in shaping that world, according to Sereno. Transient land corridors provided intercontinental bridges that also strongly affected the evolution of dinosaurs. Dinosaurs, as exclusively land-dwelling animals with a global distribution, provide the best test case for how evolution responds to the break-up of a supercontinent.
Other major evolutionary questions involving dinosaurian evolution are the focus of new work by Sereno.
"Why did it take 50 million years for dinosaurian predators and herbivores to reach their maximum body size but mammals only a handful?" he asked. "And, why is there so much empty ecospace during the Mesozoic by comparison to mammals during the Cenozoic? Where are the burrowers, the climbers, the aquatic specialists?"
The answers, Sereno suggested, lie in the posture and body size of early dinosaurs and the constraints these imposed on all subsequent evolution. Computer simulation of the fragmenting dinosaur world, Sereno says, will help us unravel the large-scale rules at work.
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