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

From: "Rob Gay" <rob@dinodomain.com>
Reply-To: rob@dinodomain.com
To: "Dinosaur Mailing List" <dinosaur@usc.edu>
Subject: Re: How Did Hadrosaurs Survive? (Was: Hadrosaur "mummy" questions)
Date: Thu, 31 Oct 2002 13:25:19 -0700

>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.

I didn't say that. A T. rex bite should be just as deadly on a hadrosaur.

>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 didn't say that; there is proof that tyrannosaurs ate juvenile hadrosaurs but not hatchlings.

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

Indeed! I pointed to the absence of tyrannosaur teeth at hadrosaur nests as evidence that tyrannosaurs didn't attack the nests or adult hadrosaurs didn't fight back.

> 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.

I only wanted to show that dinosaur herbivores in the same size range as predators needed armor or weapons if they regularly attempted to stand their ground. Some NA titanosaur armor has been reported; in any case Alamosaurus was far more massive than Tyrannosaurus and may not have needed it-although the ability to survive is not the same as invulnerability.

>But hadrosaurs were not sufficiently large in relation to tyrannosaurs for
a combative survival strategy to be credible in the absence of armor or
Size+herding behavior=good defense. Wildebeest aren't much bigger than
lions, right?

Do zebra and wildebeest herds regularly fight lions or flee, fighting as a last resort?

But lions haven't hunted them to extinction,

They are obviously coadapted, just like T. rex and Anatotitan. But T. rex initially represented a new and more effective predator, and several Edmontonian herbivores evidently could not survive alongside it.

and that's using
pack hunting, coupled with slow mammalian reproduction.

Including lions.

>>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?

Or Edmontosaurus and lambeosaurs. There is a nice illustration on page 338 of THE COMPLETE DINOSAUR.

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.

I'll say.

>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.

What other factor(s)? Didn't I already address your suggestion that hadrosaurine competition was responsible?

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)?

I just got the impression that the Hell Creek lambeosaur report may not stand up.


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