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Re: attack on dinosaur--horrific video
My point is that today, at least, this strategy is not
viable...otherwise we would, indeed, see it. But crocs are the _only_
oviparous species that "choose" defense over concealment and remote
laying. Concealment carries selection on _small_ size; whereas remote
laying selects for long distance flying.
I'm not certain that we can use absence of modern presence as a test of
viability in this case. Historical constraint also can explain the
observed pattern, which others have noted or hinted at already.
Essentially, I think you have noted a very interesting pattern, but I
see no reason to suspect that large-bodied nest defenders are not
viable in the modern ecology in a "blanket" sense, because the pattern
can be explained by historical constraint.
Archosaurs met with a major extinction event at the K/T boundary (along
with all sorts of other critters), which disproportionately affected
large-bodied, active, terrestrial forms within their clade. Thus, the
archosaurian groups that survived happen to be a semi-aquatic clade and
a smaller-bodied (on average) and volant one. The nest protection
strategies we see present in archosaurs today are thus a product of
over-representation of these two groups: both crocs and birds have been
selected to utilize their respective "aces" with regards to nest
defense. Taxa that do not utilize nests protected by location
(near-water, elevated, remote location) are probably at a disadvantage
compared to their relatives. I think you are absolutely correct that
nest-protection strategies matter, I'm just not convinced that they
matter in quite the way that you have argued above (in making whole
morphotypes/ecotypes unviable) And, of course, we have to consider
what being viable means. Do we mean that the animals would literally
be eaten into oblivion, or that they would simply have a selective
disadvantage next to oviparous species with flight and/or cryptic
approaches on their side? One could argue that if there are
disadvantages of unprotected nests, then they are largely enforced by
the presence of relatives that can fly into the treetops or hide in the
darkest corners, rather than the specific nest-attacking faunas.
Michael Habib, M.S.
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280 0181