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Largest Dinosaurs Ate Often, Exercised Little

Jennifer Viegas, Discovery News

Although no modern species precisely mirrors these theorized non-avian dinosaur rates, McNab thinks that, among terrestrial species, large varanid lizards, such as the Komodo dragon, provide the closest match. Baleen whales, which grow even bigger than the largest dinosaurs ever did, are perhaps better analogs, along with basking sharks and giant sunfish.

"They probably are reasonably thermally constant and probably have intermediate rates of metabolism," he explained.

McNab further thinks some dinosaurs became warm-blooded birds when they evolved smaller bodies and feathers for insulation.

Dinosaurs didn't just suddenly shrink into birds, however, other research led by North Carolina State University paleontologist Julia Clarke found. She and her team determined that in dinosaur lineages closely related to birds, "dinosaurs didn't stay small -- they got much larger."

Evolutionary growth spurts, therefore, seem to have characterized the development of some dinosaur species over time, with reductions followed by increases and then declines again, leading to today's much less hefty birds.

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