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Re: FW: The birds vs. the pterosaurs




On Thu, 22 Feb 2001, Jaime A. Headden wrote:

> Similarly,
> outcompeting a pterosaurs in the Early Cretaceous must also
> regard nich partitioning: in levels containing pterosaurs and
> birds, what niches have been proposed for the birds _and_ the
> pterosaurs, and which sizes are these in relation to one
> another?

Niche partitioning is a phenomenon of slightly different resource
usage by close competitors.  And, while I wisely decline to weigh in
as to which
is the better competitor (aerodynamically speaking), it is unlikely, I
think, that the two were roughly equal. After all, they were structurally
very different.  So, where we see closely related birds (finches, for
example), dividing up seed sizes on the basis of small beak size
differentials--or lizards "choosing" different tree areas based on ???--it
is difficult to propose such a minor structural differentiation
separating two otherwise cozy competitors. A more likely scenario--in my
view--is head to head competition for the _same_ resources.  These
resources may have included acquiring food or competition for nest
sites.  Then there is the related problem of avoiding
nest predation which, if you have a lousy nest site, is difficult.
I suppose you could say bats and birds have partitioned their niche--bats
(by and large) taking the night time niche, birds (by and large), the
day.  But this is presumably due to inferior flight of bats making them
non-competitive in the day; and inferior night senses of birds leaving the
night "niche" to bats.  No one proposes such a dichotomy in bird/pterosaur
niche utilization.  Were they not both trapped in the day time? 

> Some places to look: the Niobrara Chalk (mid-Plains
> States, USA), Campanian, and the Bissekty (Uzbekistan),
> Turonian; Las Hoyas, the Morrison, and the Solnhofen are avid
> producers, but true values of both forms are hardly satisfying:

Can we say that small and mid-size pterosaurs disappeared
before the end of the Cretaceous?