CORVALLIS, Ore. - Baby dinosaurs, far from being the helpless and cuddly little dependents that some research has suggested, probably cracked out of their egg, hit the ground running and didn't require much from mom or dad.
A new study by Oregon State University zoologists, to be published Friday in the journal Science, casts a different light on the early developmental stages of these ancient reptiles, and has major implications for the social structure of both baby and adult dinosaurs.
It concludes that - unlike most modern birds and many other mammal species - dinosaurs were "precocial," or born with functional skeletons and able to fend for themselves almost immediately after birth.
"It's been sort of a cherished notion that some baby dinosaurs were soft and defenseless," said Nicholas Geist, an OSU zoologist. "All modern songbirds, such as a baby robin, are blind, naked, deaf and totally dependent on their parents. People seem to like that sort of image for baby dinosaurs."
Aside from the public preference for struggling baby dinosaurs with nurturing moms, at least one scientific study of dinosaur embryos in Montana has also supported that thesis, said Geist and the co-investigator on this research, zoologist Terry Jones.
But in one of the first in-depth studies of embryo dinosaur anatomy that really explored this issue, the OSU scientists came to the opposite conclusion - baby dinosaurs were not soft, not helpless and able to run from day one.
"This doesn't necessarily mean that their parents didn't care about the babies, maybe help transport them or protect them from danger," said Jones. "We see characteristics just like that in present-day crocodiles which are clearly precocial. Their nesting habits may be similar to that of dinosaurs.
"But this study does suggest that a large amount of parental care among dinosaurs was not essential," Jones said.
In their study, the OSU scientists first looked at leg bones, an indicator that had been used in previous research to conclude dinosaurs were "altricial," or helpless at birth and lacking mobility.
They studied not only some dinosaur embryo bones, but also the skeletons of many modern animals that are both precocial and altricial, including reptiles and birds.
"Our first conclusion was that certain characteristics in these leg bones simply can't be used as an indicator of a precocial species," Geist said. "There were no meaningful differences between the various species."
But with further research, Geist and Jones found a very good indicator of the precocial vs. altricial status - the degree of "ossification," or amount of mineral deposited in the bones of the hips prior to birth.
"There is very little mineralization in altricial bird hip bones," Geist said. "It's almost entirely cartilage, which is good for some purposes; it allows the baby birds and their skeletal structure to grow very fast. But at first they are quite immobile and helpless."
Studies showed that precocial animal species, of whatever type, have high levels of mineralization in their hip bones at birth and are essentially ready to run when they are born.
The OSU scientists confirmed their findings in virtually all dinosaur embryos that have been discovered - a short list of about five - which includes both herbivore and carnivore species.
The findings make sense on a practical level, the OSU researchers say. Dinosaurs, for instance, laid their eggs on the ground, instead of in aerial nests like nearly all altricial bird hatchlings. If the dinosaur young had been born immobile and helpless they would have been susceptible to predators.
The findings of this research provide no definitive evidence to help resolve another long-standing debate about dinosaurs - whether they were warm-blooded or cold-blooded. But "this study gives no support to theories that dinosaurs were warm-blooded," Jones said.
OSU zoologists are leaders in the study of dinosaur fossils to determine what implications they may have for animal physiology and ecology.