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Re: Biped advantage



Jeff Martz asks:

> When mammals broke into the big animal scene in the Paleocene, did
> they start out with spines that were much more flexible than those
> of archosaurs?  How important spinal flexibility to fast mammals
> quadrapeds BESIDES carnivores?

I think you might be overgeneralizing about the cheetah.  Note this
from: http://www.neocomm.net/~eadams/cheetah.html

  This animal is truly built for speed. Non-retractable claws and
  special paw pads provide great traction. Large nostrils, lungs,
  liver, heart and adrenals ensure superior physical response.  The
  long, fluid body -- much like a greyhound's -- is streamlined over
  light bones. The spine works as a spring for the powerful back legs
  to give the cheetah added reach for each step. But this spring-like
  movement is very taxing physiologically. The fastest recorded speed,
  71 mph (114 kph), can be maintained for only about 300 yards (274
  meters).  Compare its stride to that of a horse --
                                 

[ "movie" of horse and cheetah running omitted because I can't e-mail
  it; go check out the site!  -- MR ]
                                                 
  -- the horse's spine remains relatively rigid and all the work of
  running is done by the legs. Over an extended distance the horse can
  outrun the cheetah. But nothing surpasses the cheetah in short
  sprints: it accelerates from 0 to 45 mph (0 to 72 kph) in 2
  seconds. One authority has proposed that this cat could propel
  itself at 5 mph (8 kph) with NO LEGS! The tail acts as a rudder for
  quick turning and even the eye is adapted for speed: the retinal
  fovea is of an elongated shape, giving the cheetah a sharp
  wide-angle view of its surroundings.

[NB: calling the visual streak a "fovea" is a bit of a stretch. -- MR ]

>      I'm trying to understand why the fastest dinosaurs seem to have
> been bipeds (with the possible exceptions of ceratopsians), while
> all the speedy mammals are quadrapeds.

Try not to get ahead of yourself!  Do you really think you know which
dinosaurs were the fastest?

--
Mickey Rowe     (mrowe@indiana.edu)