Pick one - massive or agile

["Richard W. Travsky" <rtravsky@uwyo.edu>]

http://www.nytimes.com/2010/07/06/science/06obelephan.html

It takes an elephant much longer to notice a fly and flick it away than it 
takes a shrew, and the reason is not that the elephants great brain is too 
busy with philosophy, or that it simply does not concern itself with 
flies.

Its a matter of round-trip travel time - in the nervous system. The trip 
from the elephants skin to the brain and back again to the muscles to 
flick the tail is 100 times as long as the same trip in a shrew, according 
to a new study published in the Proceedings of the Royal Society B.

The nervous system acts like an information superhighway, sending messages 
back and forth from the brain throughout the body. The bigger the animal, 
the greater the distance traveled.

Nerves have a maximum speed limit of about 180 feet per second, said 
Maxwell Donelan, the studys lead author.

It makes sense that in a large animal, like an elephant, messages have a 
longer way to travel, he said.
...


http://rspb.royalsocietypublishing.org/content/early/2010/06/24/rspb.2010.0898.full
...
As a consequence, larger animals are burdened with relatively long 
physiological delays, which may have broad implications for their 
behaviour, ecology and evolution, including constraining agility and 
requiring prediction to help control movements. 
...
Large animals may cope with these relatively long delays by simply moving 
slowly, explaining at least in part the low maximum speeds of large 
mammals (Garland 1983; Hutchinson et al. 2006) and providing further 
evidence for the idea that dinosaurs could not be both massive and agile 
(Hutchinson & Garcia 2002).
...