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National Geographic : 1993 Jan
Contents
DINOSAURS were also evolving socially during the Cretaceous. Evidence lies along an enchanting stretch of South Korean coastline known as Samchonpo, or "three thousand bays." Here embedded in petrified mud lies one of the world's richest concentrations of dinosaur footprints. "You could walk this beach all day and not run out of footprints," says paleontologist Martin Lockley of the University of Colorado at Denver. Lockley, a dinosaur trackways spe cialist, was invited here by Korean colleagues. Squalls from an approaching typhoon pelt us and obscure the craggy islands offshore. The gongyong balzaguk, or dinosaur footprints, normally draw many tourists, but today only an occasional family or group of schoolchil dren walk the Cretaceous mud flats. We stop to look at some tracks. "These belong to adult iguanodonts," says Lockley. "A herd was moving through, marching four or five abreast, like soldiers." Nearby we find the three-toed tracks of an unknown theropod in a run. Then we reach a chaotic patch of ancient mud. It looks like a trampled circus ground, pocked with foot prints of sauropods-new proof that even though that venerable family had all but dis appeared in North America in the Cretaceous, it persisted elsewhere. But these footprints tell us even more. Lockley takes out a measuring tape and kneels over one set of tracks. "Hind foot eight inches long and five and a half wide," he notes. "Front-six by four. The step is 14 inches." He calculates a moment. "The height at the hip would therefore be about three feet. This animal would be like a large dog with a long neck and tail-something you could put in a petting zoo. That's a really small sauropod. It must have been young." The ground around us is stomped over with similar diminutive tracks. Lockley has identi fied at least a hundred individuals here. He concludes that most of the tracks were made by animals in their first year of life. "Kindergarten might be a good term for this place," he says. "They aren't long out of the nesting colony. They are meandering about. Maybe they are just putting on weight." I try to imagine this colony of juveniles clus tered around an ancient lake, and I recall great rookeries I have seen. Here was evidence, surely, of birdlike parental care by dinosaurs. The evidence would grow stronger in Mon tana. There Jack Horner of the Museum of the Rockies at Montana State University in Boze man has found signs of parenting among a new genus of hadrosaurs, a family known as duck billed dinosaurs for their elongated snouts. Descendants of iguanodonts, duckbills had become the most common dinosaurs of North America by the late Cretaceous. Horner and colleague Bob Makela named this new genus Dinosaur droppings from throughout North America surround University of California graduate student Karen Chin, who looks for microscopic evidence of diet and digestive pro cesses. "In the Jurassicperiod, there were great sauropods but no flowering plants. What were those animals eating to make them so large?" she wonders. "And how did Cretaceous hadrosaurs maintain large herds in what appear to have been semiarid environments?" Dinosaurs
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