[chris (OP)]

Tweet from howard matthews‏ @howardmatthews2

Do we know if dinosaurs breathe like modern birds or like mammals?

I received this intriguing question over Twitter today. I must admit that I don't know the answer to this. Can anyone comment?

[evan_au]

In birds, their hollow bones form part of their respiratory (breathing) system.
- It appears that some dinosaurs had similar hollow bones, while others had more solid bones.
- It appears that birds sit on one branch of the dinosaur family tree, but there were many branches to this tree.
See: http://www.nature.com/news/2005/050711/full/news050711-8.html

[chris (OP)]

Birds are optimised to be extremely light; their bony frames support them in this aim by being hollow and part of the respiratory system; some dinosaurs certainly would have faced the same weight-related challenges and hence would have optimised themselves to be light. But other dinos were huge and would have had trouble supporting such a massive bulk on hollow bones; similarly elephants today have leg bones that are almost solid cortical bone with no medullary (marrow) cavity.

So where and when does this hollow bone and specialised respiratory adaptation arise in the dinosaur to bird lineage? Late, with archopteryx, or early, among the pterosaurs?

[Professor Mega-Mind]

The dino's air sac system gave them superior oxygenation to mammals .  This sustained either a higher metabolic rate , greater endurance , or greater size , depending upon the dino species .  Many mammals have high metabolisms , but non have an oxygenation system as powerful as the air sac system .             P.M.