Dinosaurs needed warm blood to jog
12 November 2009, by Sara Coelho
Large dinosaurs, such as the mighty T-rex, were warm-blooded creatures that could control their body temperature, scientists have found. With their standing posture and sheer size, these animals would never have been able to jog or even walk for long if they were cold-blooded like modern reptiles.
Allosaurs were probably warm-blooded
'You can't walk for free,' says Dr John Hutchinson, an expert in biomechanics at the Royal Veterinary College, London. 'Carrying weight around requires muscle and muscle needs energy - we know this from living animals.'
Together with Assistant Professor Herman Pontzer, at the Washington University in St Louis, US, and PhD student Vivian Allen, Hutchinson expanded this idea for extinct animals and looked at 14 different species of dinosaurs.
'This implies that modern birds inherited warm blood from their dinosaur ancestors.'
Dr John Hutchinson,
Royal Veterinary College
The team calculated the volume of muscle each dinosaur species needed to walk, jog and run at moderate speeds. They did this by looking for clues in the dinosaur's bones: 'it's possible to tell from the skeleton how much leverage each muscle had and how big each muscle had to be to keep the leg from collapsing under the body's weight,' explains Hutchinson.
Then, based on Pontzer's previous research, they worked out how much oxygen, and therefore energy, these muscles needed to function.
The team found that the muscles needed to keep an upright posture in all of the dinosaurs required large amounts of energy - and only warm-blooded animals have the high metabolic rate necessary to stay active for long.
'They wouldn't be able to walk or jog for long at all if they were cold-blooded,' says Hutchinson. And if they did manage to sustain a slow run, 'they would have to rest afterwards for an unrealistic period of time,' he adds.
Instead, it's very likely that dinosaurs were warm-blooded animals, just like modern mammals and birds.
Warm blood, or endothermy, is 'an extremely useful adaptation,' says Hutchinson. Warm-blooded animals can sustain high levels of activity. They also can control their body temperature, which allows them to colonise habitats which are too chilly for cold-blooded animals to survive in.
Although the conclusion is 'less clear for smaller species of dinosaurs,' Hutchinson believes that the study adds another line of evidence to the 40 year-old debate over whether or not dinosaurs had warm or cold blood.
The findings, published yesterday in PLoS One, suggest that warm blood evolved early and was passed on from the earliest ancestor of dinosaurs, which lived about 240 million years ago, to later species including giant sauropods, T-rexes and allosaurs.
'This also implies that modern birds inherited their warm blood from their dinosaur ancestors,' says Hutchinson adding that the conclusion agrees well with other evidence, such as insulating feathers, large lungs, and fast-growing bones, which all evolved around the same time. All of these features were later passed on to birds, which probably helped fuel their ascent into the skies.
Pontzer H, Allen V, Hutchinson JR (2009) Biomechanics of Running Indicates Endothermy in Bipedal Dinosaurs. PLoS ONE 4(11): e7783. doi:10.1371/journal.pone.0007783
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