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RE: How Did Hadrosaurs Survive?



HP Tim Donovan wrote:

> >The above scenarios are speculative. But you see, these scenarios cannot
> >be refuted,
> 
>    But are dubious.

Please elaborate.

> and they offer an alternative to your "concrete" assertions on
> >tyrannosaur behavior
> 
> Not a very credible one.

"_Any possible_ phylogenetic pattern can be 'reconstructed' if one uses
his/her 
personal imagination, or its lack, as a proof."
-- Jan Zrzavý, italics in the original

Doesn't only hold for phylogeny. It holds for all science. As an example,
have a look 
into today's Nature; there's a paper on the unsuspected ability of hawkmoths
to see 
colors even in dim starlight, 0.1 millicandela per square meter, when humans
are 
completely color-blind. Who would have imagined?

> >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.

Could you explain why, or is that under embargo...? :->

> > >   But titanosaurs were armored,
> >
> >Some were; maybe not all titanosaurs were armored, however.

Never having seen a titanosaur, I strongly suspect that all which lacked
hyposphenes 
& hypantra were armored because they needed to keep their backs straight
somehow.

>    The smaller ones, most likely to be targeted
> e.g. Saltasaurus, definitely were.

And why do you think so, if you haven't considered the above? No armor has
been found 
with the scanty remains of *Hypselosaurus*, for example, which was estimated
at 12 m 
in length and lived alongside an undescribed abelisaur that was probably 11
m long.

> > > hadrosaurs were not. Unless an herbivore is gigantic, it should have 
> > > armor or weapons if it attempted to stand its ground.

I try to imagine a hadrosaur's kick... should be very similar to a
tyrannosaur's.

> >Again, you do not *know* this.  I'll repeat what I said: large size is a
> >potential *deterrence* against large predators.
> 
>    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.

Hm... Is there a land animal alive that always fights and never
runs/walks/... away? 
On the other hand, horses, which qualify as cursorial, are good fighters
that kick 
and bite, so I think everything tries to fight if escape is otherwise
impossible.

> >  The massive strength of a
> >hadrosaur fighting for its very survival is 
> >enough to *injure* an attacking tyrannosaur.
> 
>   Possibly, but the tyrannosaur had an advantage-it was clearly 
> designed to fight and kill,

Was it also designed to _be fought_? I'm not so sure. A good kick in the
gastralia, 
and the abdominal cavity is filled with dangerous bone splinters that pierce
the 
gut... imagine the cruel details.

> the hadrosaur was not. Lacking weapons, but evolving
> hooves and keen senses, hadrosaurs would
> have fled, and fought only as a last resort.

So what? Does this mean such fighting was automatically unsucessful in the
majority 
of cases?

> >An injured tyrannosaur is as good as dead if it can't chase
> >and bring down prey any more - and you yourself has argued that these
> >guys were fast predators.  No tyrannosaur would want to risk serious
> >and debilitating injury.

This is part of the reason why the predator is _always_ at a disadvantage.
Here's 
what an intro lecture in ecology says:

1. The life-dinner principle. The prey is running for its life. The predator
is only 
running for its dinner. Occasional mistakes are fatal for the former but not
for the 
latter. Therefore the selection pressure on the former is a lot stronger
than on the 
latter. Consequently, the prey is always one step ahead of the predator in
an 
evolutionary arms race (ignoring all potentially complicated cases such as
newly 
introduced predators).

2. The prey is a moving target. As soon as the predator is adapted to a
certain type 
of prey, the target moves, because those types of prey to which the predator
is _not_ 
optimally adapted survive preferentially. Those that are common today will
have to 
die out or evolve in the future because the predator will adapt to them. It
_keeps_ 
the prey moving. Therefore it's hard to imagine that a predator kills off
its prey 
under stable conditions. To the contrary, it favors the _preservation_ of
diversity 
because it prevents strong competitors among the prey species to become
monodominant.

>    Lions are occasionally injured and bereft of their ability 
> to hunt, but they 

Not the (severely enough) injured ones obviously.

> still prey upon healthy adult ungulates.

If they can get them. Certainly happens, but certainly less often than less
capable 
individuals being caught.

> >Much better to target old, young or sick individuals -
> >those least able to fight back - as Cliff said.
> 
>    There is evidence that tyrannosaurs attacked armored dinosaurs,

1. Everything happens. Lions do attack elephants and crocodiles. But how
often? Often 
enough for natural selection to kick in? :-S

2. What is that evidence?

> and perhaps ceratopsids,

While I personally don't doubt it, what's the evidence? One unhealed bite
mark so 
far, right?

>  which are much more dangerous or tougher than 
> hadrosaurs.

How do you define toughness? As the time of survival after a tyrannosaur
bite? As the 
ability and willingness to fight, which would be the same as dangerousness?

> Also, if tyrannosaurs did not dare attack healthy adults, why 
> did ceratopsids and ankylosaurs evolve greater size to match T. rex?

Interesting logic."why did [...] evolve greater size to match T. rex?" You
have given 
an answer, and this prevents you from posing the question "why did they
evolve 
greater size?".
        Did they evolve their greater size because *T. rex* pressed them to? Did
they 
evolve it for other reasons, and *T. rex* evolved its size to stay one and
not two 
steps behind its prey?
        _Is there a way we can tell in the first place, given that terrestrial 
sediments from the time just before the onset of Hell Creek deposition are
unknown in 
NA?_ I strongly dispute this.

> The average adult size should not have changed
> if they were generally not targeted.

If predation pressure were the only possible reason for such a size
increase.

> > >  What hadrosaur would be foolish enough to fight a predator of
> > > comparable size without any obvious weapons?

_Obvious_ weapons...

> >Ummm.... any hadrosaur that wants to stay alive
> 
>    would run away as fast as possible!

As long as possible. And then it would kick, bite, wriggle.

-- 
Forgive me if I sound a little frustrated. In the Altperdino list I've
discussed this 
topic and similar effects of Ultra... er, *T. rex* :-> for months.
Nevertheless, all 
questions in this e-mail are real and not rhetoric.

:-)

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