Web Extra     October 12, 2001

Dinosaur skulls yield evolutionary clues

Thousands of fossilized dinosaur eggs from the Late Cretaceous litter the Patagonian badlands of Argentina. The site, called Auca Mahuevo, is a spectacular paleontological find. Not only does the mass of eggs reveal dinosaur nesting behavior, but scientists have also found, among the broken shells and bone fragments, intact skulls of six fetal titanosaur sauropods.

Luis Chiappe, a vertebrate paleontologist from the Natural History Museum of Los Angeles, Leonardo Salgado from the paleontology department at the Universidad Nacional del Comahue in Buenos Aires and Rodolfo Coria of the Museo Carmen Funes, Provincia del Neuquen, Argentina report their findings in the Sept. 28 Science.

With this discovery of intact dinosaur fetal skulls, Chiappe and colleagues could make inferences about the titanosaur's fetal development and their relation to other sauropods. The paleontologists analyzed cranial features such as jawbones, snouts and eye orbits of the six 4-centimeter-long skulls. They determined that the orientation of the braincase and the location of the nostrils arose independently of one another, while other cranial features "could have evolved in concert" they say.

Chiappe, Coria and others discovered the Patagonian egg site in 1998. In their paper, the authors highlight that the 71 to 89 million-year-old titanosaur skulls belong to a group whose ancestry and evolutionary development is poorly understood. Titanosaur fossils have been unearthed on all continents except Antarctica and are classified within the sauropods- a clade of large, long-necked, long-tailed, vegetarian dinosaurs. Two characteristics common to the titanosaurs are their small heads and bony-plated skin.

Jann E. Vendetti

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