Re: John Bois on Armadillos at the K/T!

[Graydon <graydon@dsl.ca>]

On Wed, Oct 03, 2001 at 03:11:11AM -0700, James R. Cunningham scripsit:
> Hi guys, for some time I've been interested in the observation that
> there don't appear to have been many small pterosaurs by the end of
> the Cretaceous -- and there don't appear to have been any large birds.
> I've wondered about the effects of mutual competition in that regard,
> especially since in the last month, I've run across some indicators
> for perhaps three giant pterosaurs in the size range of northropi, all
> azhdarchid and all seemingly larger than the probable maximum for
> birds.  What is your take on interactions with regard to size?

I'd point out that there isn't enough data to draw inferences from.
Pterosaurs and birds both fossilize infrequently, and new finds still
regularly upset the established picture of what was where when.

It makes more sense to say that in the shore environments for which
we've got fossils at all, there don't seem to be many small pterosaurs
and there don't seem to be many large birds by the end of the Cretacous,
but AFAIK, there is no site with sufficently many specimens for this to
be a comfortable statistical inference, and the places we don't have
fossils from might have been rife with large birds, small pterosaurs,
and sixty kilo arboreal sauropods, we just don't know.

On the other hand, the very largest flying birds known are barely
getting into 'medium' for pterosaurs; the flight mechanics have to have
been very different, on the basis of wing structure; and feeding
behavour for pterosaurs and early birds may have differed sufficently to
avoid direct niche competition.  It's entirely possible that smaller
pterosaurs were outcompeted by *larger* pterosaurs in the marine niches;
something had to have been driving the size increases, and it's
plausibly related to success as a skim-feeder.

-- 
                           graydon@dsl.ca
               To maintain the end is to uphold the means.