Fossils Show Dinosaurs As Stay-at-Home Dads
Friday, December 19, 2008
Did oviraptor daddies look forward to trips to the park?
Alas, that's a question the fossil record can't answer. But it does appear that many dinosaur fathers spent an awful lot of time around the nest watching the kids.
Using statistical comparisons with birds and an analysis of leg bones found atop nests of unhatched eggs, a team of paleontologists has concluded that at least three types of dinosaur males did the brooding and incubating.
The study, being published today in the journal Science, continues the extreme makeover of dinosaurs from coldblooded, pea-brain tyrants to warmblooded, empathetic helpmates.
The finding also "sheds light on the origins of parental care systems in birds," said Frankie D. Jackson, a paleontologist at Montana State University, one of the authors.
Males protect or support offspring in more than 90 percent of bird species -- a distinctly rare attribute in the animal world. In mammals, males provide parental care in 5 percent of species, and it's even rarer in reptiles.
If the hypothesis holds up -- the evidence, like that for much of dinosaur behavior, is sketchy and indirect -- it suggests that life in the Jurassic and Cretaceous was more New Age than anyone had imagined.
The researchers, led by David J. Varricchio of Montana State, examined three genuses of meat-eating dinosaurs: troodon, oviraptor and citipati. All had distinctly birdlike reproductive habits.
They laid their eggs sequentially over time, rather than in large batches as turtles do. The eggs were asymmetrical rather than round, and the shells were multilayered, like those of birds. The three types of dinosaur also produced unusually large clutches of eggs, with as many as 30 in a nest.
The scientists looked at the relationship between the mass of the adult dinosaurs' bodies and the mass of the eggs in a clutch. They compared that body-to-clutch ratio in the dinosaurs to the body-to-clutch ratio in more than 400 modern species of birds, as well as numerous species of alligators and crocodiles, which are birds' closest living relatives.
The dinosaur ratios most closely matched that of a group of primitive birds -- ostriches, rheas and emus -- that all have a "paternal model" of care of the eggs and young. The ratios were least similar to songbirds, in which both parents tend the offspring.
In between are the body-to-clutch ratios seen in other modern bird and crocodilian species in which mothers alone nurture the young.