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

["James R. Cunningham" <jrccea@bellsouth.net>]

Graydon wrote:

> > James R. Cunningham scripsit:
>
> > 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,

I don't argue this, but point out that Qsp and Qn were not found near
seashore environments.

> 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,

I would agree with this as well.

> 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.

No useful comment on my part.

> 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;

Well, my take is that they are about equally interesting for both their
similarities and their differences.  They did some things alike, they did
others differently.  Pterosaurs certainly seem to have reached larger
maximum spans, but I expect a bird wing could be designed to allow more
span.  I'm not sure the bigger bird could have still launched if it had that
larger span though.  The big pterosaurs appear to have been much better at
launching.

> and feeding
> behavour for pterosaurs and early birds may have differed sufficently to
> avoid direct niche competition.

I'm not sure I agree with that.  calories is calories, as are
opportunities.  The extensive pterosaur trackways at the Crayssac mudflat
would appear to indicate similar feeding habitats.

>  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.

Not all pterosaurs appear to have been skim-feeders, though.  Might it also
have been that the apparently increasing turbulence toward the end of the
Cretaceous may have provided favorable conditions for large soarers (more
appropriately perhaps -- motor-gliders)?

Jim