Did dinosaurs need mother love?

Paleontologist John R. Horner ruffled feathers in 1979 when he proposed that some infant dinosaurs were altricial-nestbound creatures requiring the care of doting parents. Now, two zoologists contend that dinosaurs were precocial, able to leave the nest immediately after hatching.

Nicholas R. Geist and Terry D. Jones of Oregon State University in Corvallis focus on one part of Horner's argument: that some dinosaur hatchlings had underdeveloped leg joints and could not leave the nest. To test this idea, Geist and Jones studied the femurs of newborn birds.

Emus and other precocial birds have joints similar to those of Horner's dinosaurs, yet these birds can walk just after emerging from the egg. For that reason, the two zoologists conclude that limb bones cannot reveal whether hatchling dinosaurs were nestbound or precocial, they report in the May 3 Science.

Instead, they suggest looking at the pelvis. In all altricial birds, hatchlings come out with poorly formed pelvic bones that are still composed largely of cartilage. In precocial birds and crocodiles, however, hatchlings have pelvises already formed into bone.

By the pelvic test, dinosaurs qualify as precocial, say Geist and Jones. The five known examples of fossilized dinosaur embryos all have visibly ossified pelvises, suggesting that they would have hit the ground running. But Horner, a researcher at the Museum of the Rockies in Bozeman, Mont., contends that the only way to tell the state of the dinosaur pelvises would be to slice them open-an unlikely option, given their rarity.

Horner raises other evidence to support his theories. He has found fossils of young dinosaurs preserved inside nests, an indication that they must have remained there for some time after hatching and were thus altricial. "There are no living examples of babies that leave the nest and then come back to live there," he says.