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Re: How Did Hadrosaurs Survive? (Was: Hadrosaur "mummy" questions)



HP Marjanovic brings up some very good points, but onto that I would also
like to add:
>A single bite from a T. rex could cause fatal bleeding as GSP pointed out<
Who used the example of a ceratopsian in PDW to demonstrate this, despite
your claims that T. rex didn't like to prey on them.

>Sure tyrannosaurs might've eaten them occasionally but generally they had
to go after larger, worthwhile prey<
Larger than hatchlings, yes, but if you're suggesting that they went after
adults preferentially over subadults, I think this flies in the face of
reason, and observable ecological interactions today.

>But they probably would have if adults defended the nest<
But I thought that you said that hadrosaurs would flee instead of fight...;)

>But are dubious.<
Not any more dubious than the I-say-so scenarios originally presented.

>Not a very credible one.<
Never mind the fact that you can't prove your hypothesis, I'm not sure how
you are determining credibility here.

>>Bottom line: We don't know enough (and probably will *never* know) to
reconstruct the behavior of tyrannosaurs in the type of detail you're
offering.<<
> I disagree.<
Do you have a time machine? With very few instances, the behavior of extinct
animals cannot be determined with any great certainty.

>   The smaller ones, most likely to be targeted e.g. Saltasaurus,
definitely were.<
I thought Saltasaurus was South American...Alamosaurus has no known armour
associated with it, as far as I know, though.

>But hadrosaurs were not sufficiently large in relation to tyrannosaurs for
a combative survival strategy to be credible in the absence of armor or
weapons.<
Size+herding behavior=good defense. Wildebeest aren't much bigger than
lions, right? But lions haven't hunted them to extinction, and that's using
pack hunting, coupled with slow mammalian reproduction.

>Also, if tyrannosaurs did not dare attack healthy adults...<
Look at modern ecosystems.

>why did ceratopsids and ankylosaurs evolve greater size to match T. rex?<
See David's comments, and brush up on your ecology.

>>An adult kangaroo runs faster than a kangaroo rat. An adult ostrich runs
faster than a baby ostrich or a chicken.<<
I know that my ratios aren't some sort of end-all, be-all concerning
hadrosaur speed. I know, as others have pointed out to me, that you need to
take size, individual variation, etc., into account before you can get a
rough estimate on what the data is really saying. But its at least a start,
and deals in something measurable, instead of speculation upon speculation.
Anyways, the comment: we're not dealing with sizes ranging as wide as you
have suggested. Yes an adult kangaroo is faster than a kangaroo rat. In the
gross sense, the leg length does count...to a point. But if you take two
animals close in size (me and a kangaroo), I bet the kangaroo will win. I
bet the baby ostrich will win out over the chicken too. Why? Because at
similar sizes, leg ratios matter more. How much of a difference in size is
there between Corythosaurus and Maiasaura, or Parasaurolophus and
Brachylophosaurus? I think that the sizes are close enough to _begin_ to
form ideas. Obviously, as I said, more data is needed.

>why were these taxa selected for at the expense of others?<
Because the others didn't pay the rent on time? I think that you're being
melodramatic here. Nature doesn't quite operate in the way that I gather
you're thinking it functions (then again, I could very well be wrong too).

>There is evidence that Tyrannosaurus could penetrate or cope with armor.<
And that evidence is? I don't know of any bite marks on ankylosaur armour,
but I may just not be well informed.

>Presumably tyrannosaurs attacked dorsal areas, causing extra armor to be
selected for there.<
Or they evolved more armour on their dorsal surface in order to deter
attacks from above, forcing tyrannosaurs to look elsewhere for prey.
Maybe if someone else has more precise measurements (and gives them instead
of stating that its obviously more so and so) on hadrosaur legs, we can
begin to get a better idea about what's going on between hadrosaurids and
lambeosaurs. Nature is complex, and there's probably more than one factor
leading to the demise of lambeosaurs, not just T. rex ate them all.
Let me make one final question: what data would be needed to show that
lambeosaurs weren't all eaten by T. rex, beyond the presence of a lambeosaur
(because the Signor-Lipps effect dictates that they may not have left a
record, even if present, if they were a rare component of the fauna)?
Peace,
Rob

Student of Geology
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Northern Arizona University
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