Edition: U.S. / Global

Graduate Students Dispute Idea That Dinosaurs Cared for Young

Published: May 3, 1996

Since 1978, when Jack Horner discovered a fossil assemblage of baby dinosaurs apparently killed in their nest, many paleontologists have accepted his hypothesis that dinosaurs cared for their young long after hatching. But two graduate students have challenged that idea, contending that the domestic lives of dinosaurs may not have differed much from those of modern crocodiles.

In a paper being published today in the journal Science, Nicholas R. Geist and Terry D. Jones, graduate students at Oregon State University in Corvallis, argue that the pelvic bones of baby Maiasaura dinosaurs are well ossified, strong and perfectly capable of supporting the babies outside the nest. Bone development is similar in modern baby crocodiles, they say, which are able to leave their nests and forage on their own immediately after hatching.

The maiasaur was a plant-eating genus of duck-billed dinosaur, which grew to about 30 feet. Fossilized babies in the first nest Mr. Horner discovered were about two feet long.

Mr. Horner, who is a curator of the Museum of the Rockies in Bozeman, Mont., bestowed the genus name Maiasaura (which means "fostering mother lizard") on the nesting dinosaurs he discovered in Montana, presuming that a mother dinosaur had looked after the nestlings during their early months or years. Since his original discovery he has unearthed what he said was evidence of nesting in several other dinosaur types, in which mothers may have foraged for food for their growing nestlings for long periods after hatching.

But Mr. Geist and Mr. Jones argue that this conclusion is not supported by the evidence of the bones.

They note that modern birds fall into two classes: precocial, like ostriches and most shore birds, which are able to leave their nests right after hatching, and altricial, helplessly nest-bound, like finch chicks. These two categories, Mr. Geist and Mr. Jones say, can be distinguished by their bones; the precocious species have much stronger and more developed pelvic bones supporting their leg muscles. If an analogous difference existed among dinosaurs, they argue, maiasaur babies, which had well developed bone structures for supporting their legs, were likely to have been precocious.

In reply, Mr. Horner said in a telephone interview on Wednesday that he had modified his interpretation of baby maiasaur bone development. That, he agreed, does not imply that maiasaur babies were immobile and helpless.

"Nevertheless, there is clear evidence that maiasaur babies lived in nests," he said. "If babies ventured out of their nests and then returned, as Mr. Geist and Mr. Jones are suggesting, they must have had a reason to return, and one possibility is that they gathered in the nest for feeding. You don't see crocodiles looking after their young that way."

Mr. Geist rejected this argument.

"Crocodiles make good parents," he said, adding, "Dinosaur hatchlings may or may not have been altricial, but their bones suggest they were not."