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Re: Dino Eggs and Mammals



On Sun, 21 Apr 1996, Derek Smith wrote:
> First:  If the mammals did, indeed, become better adapted for egg-eating
> near the end of Cretaceous, as John suggests, wouldn't we some sort of
> morphological change in mammals around that time, related to such a change?
> What are the adaptations for egg-predation, anyway?

Probably not.  I don't believe egg-predation requires special
morphological adaptations.  Dinosaur eggs ranged (I think) from 4mm
or so thick to 1mm.  The eggs clustered between 10-30cm long.  As for
mammals, according to Kenneth Carpenter, 90% were mouse or smaller sized,
9% were squirrel sized, 1% house cat size -- Didelphodon, which was an
omnivore. Most of today's egg-predators are omnivores.  He thinks
this size differential is a problem.  I disagree.  But perhaps this
is the most speculative part of the whole thing.

> Second:  Mammals would STILL have to compete with the various
> non-dinosaurian reptiles for those same eggs.  Is there any evidence to
> suggest that the mammals were better at egg-predation than the "old
hats" were? >

I believe behavioral adaptations made them far more efficient
egg-predators.  Extant species of mammals have it all over the reptiles.
A snake, for example, is so adapted for defence (i.e., for crawling down
small holes) that its body plan makes it an easy target: "Bight my tail
and I'll bight you back as soon as I can get my head around."  In any
case, what I am proposing does not require a sudden dominance but an
additive effect, something that tips them over the edge.

> Third:  I seriously doubt that mammals would eat the dinos into extinction
> (even if the latter were in a decline), simply because it doesn't make good
> ecological sense to do so.  If you eat all of your primary food source, you
> starve.

Island invaders eat prey into extinction.  Many different species, "old
hands," new hands, new wings, had no consideration of saving their
species--if that is what you are suggesting.  But I beg you to consider
that all individuals of all species try to maximize their own gain.  If
they are hungry, they eat (I think Confucius might have said that--or was
it Wynne Edwards?).

> Fourth:  Since the dinos' habitats ranged world-wide, and I trust, the
> mammals' as well, it seems rather odd that all dinos everywhere would
> succumb to the mammal sneakiness at the same "time".  I realize that John is
> not proposing a one-fell-swoop kind of thing, but surely there would be an
> area where there simply were no egg-eating mammals.  These dinos, then
> should have survived.

Bakker suggests alot of intermixing of dinosaur species in the Cretaceous
across land bridges and such.  If dinos travelled, mammals probably did
also.  The only place where the issue is an issue is NZ which split off
80mya (?)

> Fifth:  While mammals may have been getting smarter, so were dinos, I am
> sure.  Unfortunately, we'll really never know how smart either group really
> was at the time.

See response to Rob Meyerson.

> Sixth:  Egg-eaters or no, I still think that something very real occurred at
> the K/T boundary, and it killed more than just the non-avian dinosaurs.
> Whether it be a bolide, vulcanism, alien invasion, or a combination,
> something definitely happened.  The big sea-reptiles all vanished.  Plankton
> took a heavy beating.  Ammonites.  Trilobites.  Gone.  Mammals were not
> responsible for their demise(s).

Yes, things were happening.  But why the dinos?

> Seventh:  While the dinosaurs in general were probably not burrowers, that
> wouldn't necessarily prohibit some of the smaller ones from capitalizing on
> any burrows that happened to be handy.  Crocodiles, while not burrowers
> themselves (at least not that I know of), do hide out in burrows during
> droughts.

Mammals were better at digging burrows.  They were probably, having spent
the whole Mesozoic in them, better at protecting them, small though they
may be.

> Eighth:  While I'm not entirely sure about this point, it seems to me that a
> large portion of the dinosaur eggs found are intact.  Meaning, of course,
> they were not preyed upon.  Is this the case for Cretaceous eggs?

Many dinosaur eggs were laid and many were hatched.  They
populated the Earth for millions of years.  You can still find Nene
(endangered Hawaiin goose) eggs.  This doesn't mean they are not in trouble.

> Ninth:  The herding dinosaurs would have been better protected, not simply
> against large-scale predation by T. rex et al., but against the little guys,
> too, I would think.  If there's a greater chance of being noticed, there's a
> greater chance of being stepped on by an irate mother when you come to steal
> an egg or two.  Yet, they, too, are gone.

Burrow next to the colony.  When they leave, run up to the eggs and eat.
When they sleep, stealthily creep among the eggs and eat your fill.

> None of this is to suggest that dinosaur egg predation didn't occur, perhaps
> even extensively, near the end of the Cretaceous.  I'm just not sure that it
> would have caused the demise of all known species of dinosaur living at the
> time.
> All in all, it seems to me that any effect the mammals might have had with
> respect to the demise of the dinos would have been solely behavioral.
> Behaviors, insubstantial as they are, don't fossilize well.  So, my question
> is this:  is there any PHYSICAL evidence to suggest that dino eggs were
> being preyed upon extensively near the end of the Cretaceous?  Things like
> egg fragments (which would, of course, have to be indistinguishable from a
> normal hatching),

.apparently there is a signature inwardly turning edge of a shell.  But
this has not yet been found in a fragmented dinosaur egg.  And yet, as
you say, no one doubts that egg predation occurred...

> fossils of trampled mammals with their jaws wrapped around
> an egg, anything of that sort?

Physical evidence of any kind is absent.  It would be nice to have some.
But there is no physical evidence of any kind to indicate why dinosaurs
became extinct.  The iridium layer is evidence of an event--it says
nothing about dinosaur extinction, i.e., why dinosaurs were singled out
for the evolutionary scrap heap.  While it _may_ be a mere contributory
factor, the non-stealthy egg theory explains a great deal more thanthe
bolide event.  In the same way, physical evidence of climate change,
vulcanism, etc., is there but, again, does nothing to explain the extinction.

So, forget bolide research, and let's all go on an egg hunt!