Study: Dinosaurs "Shrank" Regularly To Become Birds

An anonymous reader writes A new study suggests that large dinosaurs shrunk to small birds to survive over a period of around 50 million years. Aside from a few large species, most modern birds are predominantly tiny and look nothing at all like their prehistoric meat-eating ancestors. The evolutionary process that governed this transformation has not been well understood, but now researchers from the University of Adelaide in Australia have put together a detailed family tree mapping the evolution of therapod dinosaurs to the agile flying birds we see today. Their results indicated that meat-eating dinosaurs underwent several distinct periods of miniaturization over the last 50 million years which took them down from an average weight of 163kg to just 0.8kg before finally becoming modern birds.

Re:Makes Perfect Sense

[Arker]

"There was a lot more oxygen in the air back then. It wasn't just hotter. With the lower oxygen levels the huge dinos wouldn't do so well because they didn't have muscles for breathing like we do."

I think you are rather badly mistaken [wolframalpha.com]. There was actually much less oxygen in the atmosphere then.

Warning, link is not really a webpage, js required :( but you can search yourself for a better source.