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Tyrannosaur gastoliths? and balance



Just some thoughts about some previous messages to the list, where
someone asked about the possibility that gastoliths might put T. rex off
balance.

If dinosaur digestion is similar to modern bird digestion, T. rex (and
other meat-eating dinosaurs) wouldn't have gastroliths.  Carnivorous
birds have thin-walled and bag like gizzards that act as storage places
for indigestible parts, like teeth, claws, bones, scales, feathers, etc. 
These parts are later coughed up in pellets and spat out by hawks, owls,
gulls, terns, herons, swifts, goatsuckers, grouse and songbirds that eat
highly chitinous insects.  

{Tangentially, wouldn't it be a rip to see T. rex cough up a pellet!?
WOW!  Better duck!}

It's mostly the plant eating birds that have the well-developed gizzards
that need grit or stones to help break up food.  Examples: quail,
pheasant, turkeys, grouse and kin; ducks and geese; finches and sparrows;
some doves and pigeons; all shorebirds; nightjar family; and hummingbirds
pick up sand for grit.

As far as I have read, gastroliths have only been associated with certain
sauropods and a few other herbivorous dinosaurs.  Could it be that
hardosaurines [for example] were quadrupedal after large meals but
bipedal otherwise, due to balance adjustments in a forward gizzard or
fermentation chamber?  Hoatzins (a tropical Amazon leaf eating bird) uses
its crop for the site of fermentation, and the keel in its breast bone is
reduced to allow room for this fermentation chamber.  Thus the bird is a
bit handicapped in the flying department, with a full crop, and it
usually  perches and sits to digest rather than clambering around. 

Would herbivorous dinosaurs be also sometimes handicapped with a full
stomach  in this way?  Certainly if this were possible, T. rex and other
predators could and would take advantage of this.

Judy Molnar
Education Associate, Virginia Living Museum
vlmed@juno.com
jamolnar@juno.com
All questions are valid; all answers are tentative.

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