“Some point out that a large saltwater crocodile can achieve a body
temperature above 30°C by basking in the sun, and it can maintain the
high temperature overnight simply by being large and slow to change
temperature.
“They say that large, cold-blooded dinosaurs could have done the same
and enjoyed a warm body temperature without the need to generate the
heat in their own cells through burning food energy like warm-blooded
animals.”
In his paper, Professor Seymour asks how much muscular power could be
produced by a crocodile-like dinosaur compared to a mammal-like
dinosaur of the same size.
Saltwater crocodiles reach over a tonne in weight and, being about
50% muscle, have a reputation for being extremely powerful animals.
But drawing from blood and muscle lactate measurements collected by
his collaborators at Monash University, University of California and
Wildlife Management International in the Northern Territory, Professor
Seymour shows that a 200 kg crocodile can produce only about 14% of the
muscular power of a mammal at peak exercise, and this fraction seems to
decrease at larger body sizes.
“The results further show that cold-blooded crocodiles lack not only
the absolute power for exercise, but also the endurance, that are
evident in warm-blooded mammals,” says Professor Seymour.
“So, despite the impression that saltwater crocodiles are extremely
powerful animals, a crocodile-like dinosaur could not compete well
against a mammal-like dinosaur of the same size.
“Dinosaurs dominated over mammals in terrestrial ecosystems
throughout the Mesozoic. To do that they must have had more muscular
power and greater endurance than a crocodile-like physiology would have
allowed.”
His latest evidence adds to that of earlier work he did on blood flow
to leg bones which concluded that the dinosaurs were possibly even more
active than mammals.
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