MEXICO CITY--As a sandstorm howled about them, 15 Protoceratops hatchlings huddled in a nest. Suddenly, an onslaught of sand, perhaps from a collapsing dune, buried them alive. Uncovered after more than 65 million years, their bones now provide the first evidence of parental care in this common herbivore. But not all dinosaurs tended their young; other new finds suggest that predatory dinos called oviraptorosaurs were more independent after hatching.
The best known evidence for dinosaur parenting comes from a duck-billed dinosaur known as Maiasaura. From well-preserved nests discovered in Montana in the 1980s, paleontologists concluded that duck-bill adults dug the nests into sand or mud, then padded them with plants. The adults carefully arranged the eggs to prevent them from rolling. In the last decade, paleontologists even found two nests with Oviraptor brooding their eggs.
The new report of the first known Protoceratops nest comes from a 1994 discovery in Mongolia, by Narman Dakh of the Mongolian Paleontological Center, in Ulaan Baatar. The 15 skeletons, each just 16 centimeters long, lay belly down on one side of the nest. All had their heads facing away from the prevailing wind, as indicated by patterns in nearby fossil dunes. David Weishampel, a paleontologist at the Johns Hopkins University School of Medicine, described the find for the first time here at the annual meeting of the Society of Vertebrate Paleontology. He believes that the young dinosaurs were siblings living in the nest and were probably being cared for by an adult. "There certainly is a family life here," says Peter Dodson, a paleontologist at the University of Pennsylvania.
Other dinosaurs, the oviraptorosaurs, may have been more self-sufficient shortly after hatching. Three fossilized eggs from a Mongolian nesting site also about 65 million years old contain partial, articulated bones. They are much more ossified than bones from other oviraptorosaur embryos, and the bone tissue indicates rapid growth. These facts suggest to Weishampel that when the dinosaurs hatched, they were relatively fully developed and may have been itching to leave the nest. Taken together, the new finds suggest "radically different strategies," says Hans-Dieter Sues, a paleontologist at the Royal Ontario Museum in Toronto.