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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.

Cheers,

--Mike


Michael Habib, M.S. PhD. Candidate Center for Functional Anatomy and Evolution Johns Hopkins School of Medicine 1830 E. Monument Street Baltimore, MD 21205 (443) 280 0181 habib@jhmi.edu