Washington: Ever wondered why some dinosaurs are so big, up to 100 feet high in some cases? Well, a new research has suggested that efficient lungs and respiration, along with egg laying, might have given them a growth edge compared to other animals.
The study, published in the Proceedings of the Royal Society B, also negated the popular theory that animals tended to become bigger over the course of their evolution.
While some dinosaurs grew ever larger over subsequent generations, not all dinosaur species became bigger as they evolved, researchers found.
"We look at the early history of archosaurs, including some early dinosaurs," said study co-author Roger Benson, a vertebrate paleontologist at the University of Cambridge.
"We can see that some lineages obtained gigantic body sizes, but others remained small and a few showed evolutionary size reductions," he said.
Benson explained that "pterosaurs, the flying reptiles, are a good example of a lineage that remained small during our study interval. There were also many small herbivores, like the dinosaur Heterodontosaurus, and small predators like the dinosaur Coelophysis."
For their study, Benson and colleagues 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 means that various evolutionary lineages did a bunch of different things, from growing larger to growing smaller.
The findings, the researchers said, counter a theory known as "Cope's rule", which claims that some groups, such as dinosaurs, tended to always evolve bigger bodies over time.
There is no question, however, that many dinosaurs were mega huge, at least when compared to on Monday's land animals.
"Several aspects of dinosaurian biology may have allowed them to obtain larger maximum sizes than any other land animals," Benson said.