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Son of response to Nick Pharris
Son of Response to Nick Pharris
The three main ideas of the non-stealthy egg theory are also the
those with which you have the most trouble.
1. Dinosaurs were less able to hide their eggs than stealthy egg-
But you say: "...(you seem) to be implying that dinosaurs were
genetically programmed to seek out nests in the open."
The only nests we have found (as you admit) are in the open.
But there are many reasons why this remains a fact. Dinosaurs
could not be small (below 1kg)! They were outcompeted in that
niche, and had been for the entire Mesozoic, by mammals, lizards
etc. But perhaps that is the wrong perspective. The proto-
dinosaur had at some point a structural change which allowed it
to move quickly in the open. This radiation into an environment
previously occupied by more sluggish reptiles was wonderfully
successful. But the taxon was _defined_ by its abilities in the
open (structurally, this probably has something to do with
digitigrade stance, bipedalism ...). In any case, it didn't mean
that the dinosaurs _chose_ to live and reproduce in the open,
rather, they were _excluded_ from close-cover by a) size (they
were above the threshhold of discovery), b) bipedalism (we've
found no small 4-leggers at all, and bipeds are easier for
predators to locate than low-to-the-ground tetrapods), c) need to
constantly visit a single location (nest), thus alerting
I assume you agree that a big dinosaur would not be
successful in close cover. All that remains is to convince you
that there could not be small dinosaurs. Well, consider this: a
small dinosaur would be defined as follows: below 1kg., non-
flying, ground-laying (in the trees they _must_ be outcompeted
for nest sites by their flying cousins), two-legged. That this
is still a defunct strategy is shown by yet another pattern:
there are none of these creatures alive today where there are
mammals. I am sorry, there are some on islands (N.Z., Hawaii)
but introduced mammals are driving these into rapid extinction.
Perhaps close-cover _was_ part of the dinosaurs' fundamental
niche, but thanks to the mammals (and others) their realized
niche was the open field. And it was there that they had to try
and cope with their problem: they could not hide their eggs!
"Gruiforms and galliforms...are successful...(and they lay eggs
on the ground. Why then would dinosaurs have a problem with
I'm not sure about gruiforms or galliforms, but the quail
and grouse also lay eggs on the ground. But they are things that
a dinosaur couldn't be: they are small (see above arguments) and
they can fly. You might argue that flying has nothing to do with
laying. Again, I would say that whether an animal is successful
or not depends upon the cumulative effect of predation at various
stages of its life. Quail and grouse suffer intense egg
predation. But in their adult stage they could perhaps escape
being eaten by flying--a thing their earth-bound cousins could
not do. Even chickens which do not fly _per se_, can get up a
predator-avoiding burst of speed. Because of dinosaurian
physiology, rapid acceleration was not their strong suit. A
small dinosaur in a turkey-style niche would not stand a chance.
They must be content with r strategies in the open-field.
2. Mammals and birds evolved new morphologies which, on top of
the already existing egg-predation ambience of the Mesozoic,
caused their demise.
But you say: "Mammals, lacertilians, and, later, snakes
(exploited eggs) all throughout the Mesozoic (and) were just as
capable (at egg-predation) as modern mammals."
This is a statement which seems to deny the possibility that
evolution has any effects whatsoever. I am always astounded when
I hear Gould voice this same idea: "The mammals had lived under
the feet of the dinosaurs right through the Mesozoic. They were
small, insignificant creatures which gave the dinosaurs no
trouble. It was only when the dinosaurs died that these little
creatures walked into their empty niches. If dinosaurs were not
removed from the Earth there would be no humans...to ponder the
nature of science..." and so on. This is more polemics than
science. So, too, is your comment about "mammal Chauvinism."
What do we know? Mammals, over the Mesozoic evolved in many
crucial ways (see reproductive comments in another post-this will
have to wait until tomorrow night). Fending for themselves in
the small-animal niche, they developed brains with more neurons--
they could, towards the end of the Cretaceous, out-think all
other animals. An advantage of this was that they could create a
representation in their mind of things they could not see. They
could behave with more flexibility than the dinosaurs who
probably remained slaves to fixed action patterns. They could
solve more complex puzzles, such as: "How can I make it to this
burrow or that branch in the quickest possible time."
Computational power also made them better optimal foragers--i.e.,
all other things being equal, because they spent less time
foraging, they could spend more time rearing--though I know birds
are incredibly efficient foragers, so strike this.
Cranial capacity increased over the Mesozoic. But so did
their hearing, vision, locomotion--the primitive ricochetal hop
allowed them to move quickly into the open-field. But this, in
turn, gave them an advantage that small (juvenile) dinosaurs
didn't have: because their hop was powered by two legs, they were
probably able to avoid predation from the air. I say this
because all the small mammals which today live out in the open--
rabbits, jerboas, potoroos, kangaroo rats--most likely avoid
predation with the rapid acceleration of a hop. In fact, in a
beautiful example of convergent evolution, many of them have a
banner tail, presumably to provide a decoy target for the hawk or
These adaptations could certainly have increased their
effectiveness as egg-predators.
But what also of the birds? (I'll discuss this in response to
Thomas Holtz--another day)
3. Mammals, birds, snakes, lizards, and dinosaurs preyed upon
dinosaurs until they became extinct.
You believe that extinction by predation is a rare event and
that creatures tend to follow the lynx/hare model of pred/prey
oscillation. You didn't like my island analogy, but you
addressed it in a way which suggested you didn't understand it
(or perhaps it's my lit. expression). The egg, inasmuch as it is
an unevolving form, a fixed entity, is unable to respond to
predatory pressure (yes, the parents can develop strategies, but
these are ultimately constrained by the limits of the eggs and
their physiology--i.e., their ability to protect it in some way.
They could not burrow with any skill--because of their
biomechanical deficits, perhaps?--and they could not fly, and
they could not hide because they were big. They did build
communal nests but there had to be a limit to how close they
could be to each other: "Hey, don't step on my eggs!" Big egg-
laying animals can only do so much). Because the dinosaur
strategy had so many restrictions, it resembled an island species
in that it could not respond to new, species evolving around
them. Though this was sympatric evolution it resembled allopatry
in that one species evolved while the other could not.
If that is a tortured analogy then try this one. The
different species who would attack the egg and drive it to
extinction were like the fishermen of New England. In this
Tragedy of the Commons, the fishermen destroy their livelihood
EVEN THOUGH THEY KNOW THEY ARE DOING IT!!!!! The fish probably
would have been alright had the fishermen not developed fish
radar, etc. But unable to respond to this new technology, they
succumb. Dinosaurs, I submit, due to their body plan and their
eggs, could not respond to the new technologies coming off the
mammal and bird lines.
Look, I know these analogies don't take the place of actual
examples of sympatric preying to extinction. But we live in,
evolutionarily-speaking, stable times. However, I believe there
were times when radically new morphologies had an impact
(whoops!) on other species. Biological perturbations such as
angiosperm development, photosynthesis, the move to land,
encephalization, the development of the egg itself, all these
things had profound effects. Looking at the world
as it is today, and inferring biological history to the last
detail, i.e., predators never destroy their prey,
is a narrow view. And, though I don't have direct evidence to show it, I
believe developments in predatory abilities were always a powerful motive
force in the creation and extinction of species.