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Re: The biggest dinosaurs



Re: The biggest dinosaurs

On 20 Aug 1997, Norton, Patrick wrote:
 > ...does anyone have any thoughts about why the upper absolute
 > size of dinosaurs was so much greater than the upper absolute size
  > of terrestrial animals today?

   I always thought it was due to the teeth and food availability.
   A sauropod can reach just about everything.  Assuming they used stomach
stones to help digest their food, they could eat all day long.  The
ability to replace old teeth would not limit their size.  Their long necks
allowed them to get at most types of vegetation.  One limiting factor for
sauropods would be if the forests or vegetation that they fed on became
broken up and separated into regional pockets.  These pockets would
eventually change and kill off all the sauropods in those local areas.
Flowering plants might have allowed the evolution of rapidly reproducing
plants and trees that could replace old forests that the sauropods fed on.
 I can?t help feeling that the plight of the elephants, mammoths, and
mastodons is not similar.  Once their regional pockets they lived in were
gone (due to expanding deserts, glacier advances, expanding grasslands,
farming and shepherding man) these animals are/were doomed.  Low grazing
dinosaurs co- evolving with plants that could store energy in their roots
to recover from grazing or fruiting plants that could be spread by grazing
animals might have helped isolate sauropod pockets.  Add in some inland
seas. mountain ranges, large fast flowing rivers, and fragmented
continents and the problem becomes worse.  Those locations where the
pockets did not disappear probably had the largest late sauropod
dinosaurs.
   Mammals, once their teeth are warn away would die of starvation.  Some
of the larger, like Elephants have more than 2 sets of teeth to help
overcome this limitation but even they can starve to death after their
last set is worn away.  In addition, animals  that spend some of their
time rechewing their cud possibly limit their size because they can not
spend that lime intaking food.  (note, I think the 2 sets of teeth is also
the reason it took mammals so long to achieve large size after the
dinosaurs died).
   The dinosaurs with dental batteries for chewing food had replaceable
teeth that would at least eliminate the starving limitation.  Even so,
they would have to spend some of their time chewing their food that they
could otherwise spend intaking food.  As a result, I think that the upper
limit for dinosaurs with dental batteries might be similar to that of
elephants and their relatives.
   Predatory dinosaurs would need large prey over many generations to
achieve large size.  Their replaceable teeth might have allowed them to
recover easily from teeth lost in dynamic attacks.  Take a modern cat or
dog and take away its canines and it would have trouble surviving.
   Some whales reach large sizes because of the food population at their
disposal that their teeth do not prevent them from intaking.  When their
food goes, they too will disappear.

Remember, replaceable teeth when thinking of dinosaurs.  At least until
beaks started to develop.
        Mark Shelly