Friday, March 9, 2012
In addition to this question, why were some dinosaurs massive and what allowed them to reach such huge sizes.
For the answers to all these questions and more check out Rise of dinosaurs reveals major body-size transitions are driven by passive processes of trait evolution in this months Proceedings of the Royal Society B.
There's also a commentary on the DiscoveryNews website.
Benson and colleagues Roland Sookias and Richard Butler analyzed more than 400 species spanning the Late Permian to Middle Jurassic periods. The animals' pattern of growth during 100 million years supports a theory called "passive diffusion." This just means that various evolutionary lineages did a bunch of different things, from growing larger to growing smaller.
The findings counter a theory known as "Cope's rule," which claims that some groups, such as dinosaurs, tended to always evolve bigger bodies over time.
"Several aspects of dinosaurian biology may have allowed them to obtain larger maximum sizes than any other land animals," Benson said.
"For example, in many dinosaurs, parts of the skeleton contained air, and we think they had an efficient bird-like lung. These features helped them to support their weight on land more easily, and made their respiration and heat exchange more effective than in mammals."