Egg-laying, Not Environment, May Explain the Size and Downfall of Dinosaurs

ananyo writes "Paleontologists have argued that dinosaurs were able to grow quickly and fuel large bodies when temperatures were warm, oxygen levels were high, and land masses such as the supercontinent Gondwana provided abundant living space. But two new studies contradict that idea and suggest the key to some dinosaurs' vast size lies in the limitations of egg laying. In the first study, researchers examined whether changes in body size followed changes in environmental factors and found no correlation. A second study argues that the reason dinosaurs grew so large was because they were forced to produce relatively tiny young (abstract only), as developing embryos would not be able to breathe through the thick shells of large eggs. When the young of large animals start out small, they must grow through a large size range before reaching adulthood. As a result there was intense competition between small and medium-sized dinosaurs, forcing adults to keep growing until they reached very large sizes to gain a competitive edge. But being big also had drawbacks. When an asteroid impact 65 million years ago wiped out most large-bodied animals, there were so few small dinosaur species that the group was almost obliterated, with only the birds surviving."

Re:Circular reasoning?

[mcgrew]

I RTFA and it looks like hogwash to me. It said that the adults had to be big to keep from being eaten by their own young. It seems to me that cannibalism would be an evolutionary disadvantage, plus the biggest dinos were herbivores. And I notice that most large animals today are herbivores -- elephants, cows, rhinos.

Perhaps the article was poorly written, but it doesn't seem logical. The only logical part was that the larger animals became extinct when the asteroid hit.

Re:Few is not the same as none

[Timtimes]

I got this one. The larger dinosaurs were dependent on larger trees and vegetation that takes longer to repopulate after the asteroid hit than their life cycles would allow. The growth cycle of a tree is many orders of magnitude slower then reptiles. So at first there would still be a lot of small babies of big (dead) dinosaurs to compete with the smaller dinosaurs (that evolved into birds?) from the short grasses that would emerge post fireball. The large bodied dinos would ultimately die when they got too big to consume enough of the smaller vegetation to allow them to exist. This is as good as example as I can think of off my head: You could, for example, try to reintroduce a particular species of extinct locust that used to exist until the late 1800's and it wouldn't do any good. They only bred in the deepest ruts of the prairies before the vast buffalo herds got slaughtered (Arizona history books mention that were all wearing hoodies). You could theoretically release the first "batch" of artificially created/cloned buffalo locusts into the wild, but when it came to the point in their life cycle to breed, they wouldn't have anyplace to lay their eggs. No herds of buffalo. No eight foot deep ruts in the prairie worn down over eons for them to lay their eggs. Enjoy.

Re:Circular reasoning?

[dylsexia]

In Canada, we refer to them as the Bloc Quebecois.