Re: gigantism as liability

[Graydon <oak@uniserve.com>]

On Sun, Nov 16, 2008 at 11:26:20PM +0100, David Marjanovic scripsit:
>> if sauropods relied strictly on numbers it is hard (for me) to come
>> up with a scenario whereby babies who are defenseless at chicken
>> size, who would have had predators at least all the way up to
>> elephant size, could avoid total reproductive failure.
>
> Perhaps by growing fast -- much faster than any turtle.

Cryptic colouration, body form, temporary arboreal habitat, and
scuttling through the undergrowth all come to mind as possibilities as
well.

Most prey species, even quite large ones like deer, put a lot of effort
into being hard to detect.  No reason to suppose juvenile sauropods
wouldn't have similar adaptations.

> Also, I think sauropods were well able to put up a fight against any
> predator up to around their own size, considering the thumb claws and
> the tail and all.

Are there any known juvenile sauropods complete enough to tell when the
tail whip mechanisms or clubs formed?

> What we really need here is a way to quantify all these factors, and
> that's going to be difficult... 

Well, I can think of a bunch of things we'd expect if there were active
nest defense going on; we'd expect lots of parental tracks around the
nest site, we'd expect _either_ tight nest grouping (if there's any
communal defense going on) or very wide or no nest grouping (if adult
sauropods have to fit between their nest and the nest of the next
sauropod over); we'd expect to see some evidence of nest occupancy by
the hatchlings; if a parent is defending them, they're better off
staying there instead of sprinting for the weeds.

So far as I know, these are all known from Maiasaurus but are not known
from any sauropod.

Quantifying survivability *might* be possible with enough specimens
along an ontogenetic series, but I don't think there's enough specimens
of anything, never mind one species of sauropods.

Though, thinking about it, if there's any way to get an adult population
estimate and an egg count at the same time, there's probably an
eggs-to-adult ratio lurking there, that could be compared to known
ratios for living species.

-- Graydon