Re: "Digging Dinosaurs"

[John Bois <jbois@umd5.umd.edu>]

On Thu, 29 Jul 1999, Betty Cunningham wrote:

> how about modern quadrupeds like the florida panther-capybaras-rats-musk
> rats-beavers-jaguars-deer-alligators-foxes-water buffaloes-hippos-

Part of the problem is defining a wetland.  They include swamps (like
Everglades), bogs, marshes, potholes, even ephemeral swamps which are
only occassionally inundated.  Some of the animals above can cope with
some of the habitats I just mentioned.  I suppose the limiting factors for
many are 1) depth of water; 2) area of wetland.  A racoon can enter a
swamp to forage but must return to dry land to rest (or go up a tree, I
suppose). This
essentially limits the area it can forage and thus gives a refuge from
predation.  Lowering the water level of swamps increases predation by the
animals above because it provides greater access (ref. if needed).
Animals, eg., water buffalo, may have adaptations preventing hypothermia
(eg., small proportion of surface area immersed).
What are the issues for dinosaurs?  Keeping eggs dry.  Keeping parents
warm (if endothermic).  
I agree that small, light dinosaurs may have been able to nest in some
swamps.  I think the risk of egg drowning may have been a limitation
relative to birds which lay in reeds, trees.  Another limitation would
probably be crocs which, if the water depth was appreciable, must have a
significant advantage in combat.
One thing was apparently true--there were alot more swamps then than
today.  Also probably alot more diverse kinds of swamps, I mean large
areas of semi-inundation perhaps, which might have been ideal.  Archibald
notes that the disappearance of the Pierre Seaway which occurred at the
end of the Creatceous may have significantly reduced this habitat.  He
feels this was an important factor in extinctions.
Also, a relevant piece of info is that the extinction of Diatryma
coincided with the disappearance of wetlands in both Europe and America
although they occurred at different times.  This suggests that it depended
on wetlands.  And if D. got by, I can see no reason why non-avian dinos
couldn't do the same.