[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Bird/hibernation/torpor

On Sat, 29 Mar 1997, Bettyc wrote:
> Mammals may be rarer simply
> because if they were burrowers and were covered by a sandstorm, they
> were likely able to escape.  

Thank you.

> Sea turtles don't have elaborate built-cover for the eggs beyond sand or
> parental protection of their young, and they managed to survive the KT
> just fine.

But they are stealthy in a way dinosaurs probably were not.  First, they
are very secretive about laying (popping out of the water at a remote site
on one night a year in the middle of the night); second, they lay and
leave.  This avoids predator alerting parental investment visits to the
nest.  I think there are reasons (and in some cases, evidence) why dinos
are thought to stay around the nest: birds seldom (never?) lay and leave;
dino eggs needed temp. regulation; huge diurnal animals cannot lay their
eggs in secrecy.

> I believe that the discomfort is with the idea where you've said
> (something like) "mammalian egg-predation is a major cause of dinosaur
> extinction".  Well, maybe on an individual basis, but I don't see all
> species of dinosaurs represented at the KT suddenly being hit with a
> biblical plague of rats.....seems very untidy in a scientific way.

I wouldn't put it exactly that way.  Look around today.  All egg layers
must take care to hide their eggs, or else a horde of animals (mammals,
birds, snakes, lizards) will eat them.  To accomplish this snakes lay in
places which are hidden or inaccessible to other body plans; ditto
lizards; birds fly to out-of-the-way, or inhospitable places; crocs are
restricted to places they are sovereign; turtles are super-stealthy with a
lay and leave strategy; and mammals incubate internally.  _All_ of these
strategies have been formed in the crucible of nest predation. And they
define the existence of these creatures.  They also define the winners and
losers at the K/T, i.e., dinos were not, by and large at least, stealthy
egg layers.

 At the K/T a similar group of animals enjoyed eating eggs and hatchlings.
My idea is that there was business-as-usual egg predation going on
throughout the cretaceous and, at some point, over some length of time,
probably in concert with enironmental stress, this pressure overcame
animals who were heavily invested in defence over stealth.  My challenge
is to show with parsimonious arguments how this may have happened and,
to hold the _idea_ up to the light of available _evidence_.  1. Dinosaur
diversity declines (they were closed out of the small animal
niche--mammals probably had a role in this); 2. They become more invested
in defence, i.e., they become bigger.  Nest predation (I argue--and nobody
has, as I remember, challenged this idea) is a good argument for this as
without the non-stealthy, fixed-site baby problem species would be better
to run than fight (as do just about all creatures today!); 3. And,
finally, on top of all this a new and probably threatening coterie of
species burgeoned toward the end of the cretaceous (birds representing
extant species--not just loon/tern morphs, but almost certainly
eagle/hawk/vulture morphs; mammals--cat-sized, squirrel-sized, rat-sized,
behaviorally enhanced, night-seeing).

Well, I claim the "plague of rats" model doesn't reflect available