[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Archaeopteryx and Flight
>From: NEIL CLARK <NCLARK@museum.gla.ac.uk>
> > Second, there *was* competition.
> Birds may now fill the niches that pterosaurs once held, but this in
> itself is not evidence for direct competition between them. As far as I
> know there is no evidence that birds did compete openly with
Well, the evidence that the particular pterosaurs that filled the same
niches as early birds died out long before the others did is highly
suggestive. Combined with tghe fact that niches usually do not become
empty once filled, and the inference is very strong.
Also, competition is rarely "open", even where it happens it is
often covert, and even highly indirect. As small a thing as a
higher speciation rate, allowing birds to more quickly replace
the normal background extinctions of individual species might
have been enough.
> I'm sorry, I don't know when the 'fly-catching' pterosaurs died out.
> Was it at an extinction event horizon or nearby?
Which extinction event?
They died out some 40 to 60 million years before the terminal
Cretaceous mass extinction. *Some* workers believe there was
a terminal Jurassic mass extinction. They *might* have died
out then - *if* it occurred. (Actually, here my memory is somewhat
uncertain too, I am not sure if there are known Early Cretaceous
pterodactylids, or other small, toothy forms in the Early Cret.).
> I don't think that there are enough fossils to swing this debate one
> way or the other at the moment. I would like to know why we don't
> have more fossils of birds with fossils of pterosaurs if they were
> fighting it out.
There is some 70 million year of overlap - from the Late Jurassic
to the end of the Cretaceous. *Both* groups have an exceptionally
*poor* fossil record, mostly due to their extremely fragile bones.
Also, "fighting it out" is probably not how this sort of "competition"
is worked out. An established species can only rarely be ousted by
direct competition with an ecologically similar species. The key
points are the establishment of new species to replace the normal
losses to extinction, and the expansion of ranges into newly available
territory. Once the new species is in place, then *it* becomes
resistant to ouster. If the majority of the new species belong
to one group compared to another, then eventually the group with
the higher rate of new species formation will rpelace the slower
one. This is competitive, since it is competitive exclusion that
stabilizes the established species against replacement.
The fossil record here is *very* similar to that during the rise of
the rodents to replace the multituberculates. There is a similar
piecemeal die out of the MT's and a gradual increase in the diversity
of rodents. There are relatively few cases of ecologically rodents
and MT's in the same fauna. (Although many faunas have members of
both groups, the co-occurring forms are generally not in direct
Also, considering that some rather specialized water birds are
known from the Late Cretaceous, it is fairly clear that some
rather specialized birds of ohter sorts had to already exist.
[This can be confirmed by cladistic analysis of the relationships
of the water birds to other living groups, showing that forms
similar to certain living groups had to exist *prior* to the
evolution of certain aquatic groups].
The peace of God be with you.