Fair questions to ask might be: why has the new taxon moved into all of the other niches...and what is the delay in taking over the large-size niche? Are the large sized species immune to the forces that eliminated the globally
distributed smaller species?
A good starting hypothesis might be that there
was something in the biology of the entire taxon that predisposed it to
global extinction. To propose a biological mechanism is not teleological.
Indeed, we apply such knowledge of predisposition-to-extinction today: e.g.,
island species are predisposed to at least local extinction due to no
defenses against continental predators!
I know you recognize that most community structure is the result of competition/predation past...a war-like battle to be sure!
I absolutely agree with this _except_ in the case where an entire
clade--pterosaurs--were selected in one direction, for one trait: bigness.
This suggests (to me) a selection _against_ other traits. I mean, to argue
for niche abandonment rather than niche replacement is romantic: species
don't simply give up niche space.
I would have thought that a prime engine
of morphological diversity was the tendency to divide up similar size class
niche among more species.
For sure, the number of actual niches has _increased_ over evolutionary time.
Because we have more critters.
I'm not saying there is _always_ a biological answer--just usually. And so,
the questions, at least, are valuable.
Absolutely.
Today's marine soarers care for non-flying baby for several months. This
requires a predator-free island with close-by resources. I mean, parental
investment is very high in these species--this is "demanding" by definition!
But there are several coastal species...and who knows what was around then.
I realize this is guesswork...but, with the likely pre K/T split, the
question of predatory birds influencing global community structure is now
askable.
I find this hard to believe. Are you talking from a standing start? Half a
second? For an animal with a ten meter wing span. Something like this is
shown on Walking with Dinosaurs when Q quickly takes off. My students are
quick to cry "fake"at this representation of a quick take-off. Looking to
be informed.
Finally, on the issue of whether or not large soaring pterosaurs were likely
to be replaced by birds with or without a global catastrophe: I am of the
impression that (absent man, at least) albatrosses are limited more by
predation/competition for predator-free nest sites close to food than by
food availabitlity _per se_.
As such, the survival of a particular soarer
is likely dependent upon either its ability to drive a competitor off an
island or its ability to nest at more inaccessible sites.
I would be
interested on your view about pterosaur latitudinal distribution and fish
abundance in tropical vs. arctic regions.
Cheers,
--Mike Habib