SCIENCE NEWS Vol. 149 June 20, 1997

Pg. 280-81

By Tina Adler

Summary by Jenny Thurman


John R. Horner, a paleontologist made waves with his view that baby dinosaurs were altricial, creatures that are nestbound and require the care of their parents. Two zoologists feel, however, that dinosaurs were precocial, therefore able to leave the nest after hatching. The zoologists, Nicholas R. Geist and Terry D. Jones from Oregon State University, are focusing on one point of Horner's view: dinosaur hatchlings had underdeveloped leg joints and therefore could not leave the nest. Geist and Jones have tested this theory by observing the femurs of baby birds.

Emus and other precocial birds have leg joints that are similar to that of Horner's dinosaurs. These birds, however, can walk just after hatching. Geist and Jones have concluded that Horner's leg joint theory does not reveal whether the dinosaurs were altricial or precocial.

Geist and Jones suggest that the pelvis bones may be the answer. In all altricial birds, the babies have weak pelvis bones that are largely composed of cartilage. In precocial birds and their reptile relative the crocodile, the pelvises of hatchlings are already formed into bone when they emerge into the world. The dinosaurs have bone composed pelvises and therefore would have been fully mobile after hatching.

Horner who is a researcher at the Museum of the Rockies in Bozeman, Montana, opposes the Geist-Jones theory. It is his contention that the only way to observe a dinosaurs pelvis would be to dissect one, which is not probable.

Other evidence Horner offers in support of his idea results from fossils found of young dinosaurs preserved in the nest. He maintains that the dinosaurs must have remained there for sometime, proving they were altricial.