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the ankylosaur/nodosaur thing



On 3/28/96, A. GWIN wrote:

>Everyone seems to have missed my point concerning the
>ankylosaur/nodosaur thing. What I was really asking was this: Did
>nodosaurs have any kind of defensive advantage over ankylosaurs? I
>realize their differences, and it seems to me that nodosaurs were
>rather like ankylosaurs with less defensive capability. They had
>slightly less armor and no tail club, so what did they have? They
>couldn't have been much faster than ankylosaurs, and obviously were
>slower than their potential predators. Perhaps they had heightened
>senses of smell and sight, or travelled in herds, unlike most
>ankylosaurs, which make good candidates for solitary dinosaurs.

A comparison with living animals might be helpful here.  Do elk and moose 
have any advantage in the face of predation over mule deer?  After all, 
they have larger antlers than mule deer.  Are pronghorns at a 
disadvantage compared to mule deer, since their horns are smaller than 
the deer antlers?  Then, does the advantage switch to pronghorn when the 
deer drop their antlers?  Are goats a step below pronghorns, perhaps 
needing heightened senses of smell and sight to compensate for smaller 
horns?

In a different vein, do "horned lizards" have an advantage over less 
prickly lizards in the face of predation?
 
Actually, I don't know the answer to any of those questions.

Maybe I've missed the point, too, and I don't mean to be comparing apples 
with oranges, but I suspect that predator/prey relationships were about 
as complex during the Mesozoic as today.  We might be prone to make 
superficial, anatomy-based inferences about dinosaur 
lifestyles/competition were it not for sobering comparisons with living 
animals.

Have nodosaurs ever been found, untransported, in the same bed (i.e., 
right next to) ankylosaurs?  If not, then we can't say that they ever saw 
each other.  Did the same predators, with the same abilities, feed (or 
try to feed) on both?  Perhaps _Daspletosaurus_ fed on ankylosaurs, but 
_Albertosaurus_ fed on nodosaurs (and something else fed on the third 
group that Tom mentioned).  Then again, perhaps _Daspletosaurus_ and 
_Albertosaurus_ only scavenged dead ankylosaurs (I know the 
counter-arguments), so comparison of armoring, speed, sense of smell, 
etc. in ankylosaurs is not very relevant.

My point, again, is to beware of the strong temptation of overinterpret 
the data. 


*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
Norman R. King                                       tel:  (812) 464-1794
Department of Geosciences                            fax:  (812) 464-1960
University of Southern Indiana
8600 University Blvd.
Evansville, IN 47712                      e-mail:  nking.ucs@smtp.usi.edu