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Re: cause of Gigantism in sauropods



a problem with the parental care theory in sauropods is the sheer size
of the adult compared to the egg - it simply is not practical to
protect the nests! Same for babies..... it would be extremely
dangerous to be a baby elephant (~100 kg) running around between 20
ton adults (and it can be dangerous for baby elephants in a herd of
adult elephants of only ~ 5t). Additionally, clutch size and placing
(in the few cases where they are known) do not support parental care,
but rather abandoning of the nests by the adults.
Furthermore, fast growth alone is not a solution to protect yourself
from predation: what about the +/- decade you need to be so big that
you can counter an attack by a big theropod? Oops!

btw: lions can kill elephants, albeit at high risk. They just need to
learn how to do it.

Cheers,
Heinrich




On Mon, Feb 7, 2011 at 7:01 AM, Augusto Haro <augustoharo@gmail.com> wrote:
> 2011/2/7 Dann Pigdon <dannj@alphalink.com.au>:
>> On Mon, Feb 7th, 2011 at 2:30 PM, John Bois <mjohn.bois@gmail.com> wrote:
>>
>>> ... I would have thought it would rate a mention as an important difference
>>> between extant mega herbivores and those of the Mesozoic. Indeed,
>>> comparisons are frequently made between the two groups: early in the
>>> paper predation is given credit for being the potential major
>>> selective value of large size, i.e., it drives selection. This
>>> apparent contradiction with the paper's thesis is resolved by saying
>>> that sauropods, like elephants, outsized their predators, and that is
>>> was limits on predator size (possibly due to bipedal body plan) that
>>> made this no longer a driver of selection.
>>
>> The problem with growing large to outgrow *your own* predators is that you 
>> first have to survive
>> long enough for that to happen. This would have been especially difficult 
>> for sauropods who started
>> off so much more relatively smaller than their adult form, and who didn't 
>> have the benefit of super-
>> rich milk (a la whales) to grow fast on.
>
> It seems, as far as I read, that histology suggests fast growth rates
> for large dinosaurs, especially sauropods. Fast bone growth rates for
> hadrosaurs have actually been seen as a way to avoid predation. I read
> a paper (I think from Erickson) where it is claimed that Tyrannosaurus
> grew faster than modern elephants.
>
>>> Now, I have been nursing my own pet hypothesis for a score of years, a
>>> hypothesis that argues that large size _was_ driven; driven by the
>>> fact that dinosaurs above a size that inhibited concealment, had
>>> to--if nest attendance was in operation--defend or abandon the nest.
>
> What about exploiting a previously unexploited resource? (tree tops,
> for example). Generally speaking, larger animals can, also, bite
> harder, and are thus perhaps able to eat thougher stuff, although this
> is not likely the case in sauropods. Large size can also expand the
> preferred range of food in the case of predators, for tigers can hunt
> from locusts to gaur, and I suppose the range is much lower for
> smaller cats (may there be something similar in herbivores, accounting
> for greater possible forces and thus an increase in the potential
> range of size and thoughness of the exploited resource?).
>