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RE: the unkillable hadrosaur thread



One thing to remember is that hadrosaurs might not have had any
specialized defense mechanism.

Most mammalian herbivores do not have specific structures dedicated to
defense.  Both the African or American plains are full of herbivores -
zebra and various species of antelopes, bovids etc. which lack such
specialized features.

Some, like zebra, kick with their legs when attacked, but that is surely
secondary to the primary function of legs.  Many have behavioral
defenses (herding, posting lookouts, alarm calls, migration,
simultaneous birth), but there are not directly and unambigously
reflected in their osteology.   Some have horns or antlers which can be
used secondarily for defense, but the primary function seems to be
intraspecies combat and sexual selection.

Put another way, they might have survived with a combination of
secondary defense mechanisms, combined with a high enough birth rate to
compensate for losses.  

While trying to escape a predator, a hadrosaur might well have whacked
it with its tail as part of a mad, thrashing scramble to get away.
However, this sort of accidental or secondary use might be hard to
prove.

One more point.  Hadrosaur tails are big - a large fraction of total
body length (up to nearly half).  They are typically stiff and would
have stuck out behind the animal.   Suppose that at predator is coming
from the rear, trying to grab a hadrosaur that is trying to move away.
The tail would be the largest and most likely target for the predator to
grab or bite.

Not the best target mind you, because it is not exactly a vital organ.
However, if the hadrosaur is about to escape, better grab the tail than
anything else.  Once ahold of the tail the predator would presumably try
to knock the hadrosaur over and then proceed to a more deadly attack.

So, if you consider at "close calls" where a hadrosaur was injured, but
got away, you might expect a large fraction to have a tail injury.
This might explain the kinked tails.  Thus, evidence of broken tails
might tempt one to conclude that the tail was a defense mechanism, when
in fact it was just the nearest thing to grab.

Ken Carpenter has a hadrosaur tail (an Edmontosaurus, as I recall but
might be wrong) that appears to have a bite taken out of it by a
theropod tooth - and which seems to have subsequently healed.   There
may be other specimens like this.


Nathan

> -----Original Message-----
> From: Pat Grant (Library: Serials Catalog
> [SMTP:PATG@vax2.concordia.ca]
> Sent: Thursday, May 22, 1997 8:56 AM
> To:   dinosaur@usc.edu
> Subject:      the unkillable hadrosaur thread
> 
> Since nothing else seems a satisfactory explanation, perhaps we should
> take another look at the tail-thwacking theory of hadrosaur defence. 
> Some people objected to the idea because it would be likely to cause
> severe tail damage even if it worked--but then, Darren Tanke pointed
> out a few months ago that broken tails were frightfully common among
> hadrosaurs, and often rehealed with kinks in them.  (He was hoping
> somebody would illustrate kink-tailed hadros.)  So, is the observed
> tail damage consistent with what could be expected to result from
> using the tail as a bludgeon?
> 
> Pat