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Cloacae, Uricotely, Climates, and Bacula (was Re: Jurassic genitals)



At 10:09 PM 7/17/98 -0400, Mike Teuton wrote:
[With regards to the almost certain presence of cloacae in dinosaurs...]

>I thought that might be the case regarding cloaca.  I brought this up to
raise the
>issue of conservation of water.  GI  and urinary losses in animals with
cloaca are
>AFAIK less than mammals.  So if dinosaurs did not sweat and had relatively
small
>GI and urinary losses then most of their insensible water loss would be
>respiratory.

What is more: as sauropsids/reptiles, dinosaurs were almost certainly
capable of uricotely: eliminating their wastes in the form of uric acid
rather than urea (the primitive condition found in mammals, amphibians,
etc.).  Uricotely is very useful at conserving water.

>  In a hot humid world this would be little as well.

One note of caution: the period from the beginning of the Late Triassic to
the K-T boundary is twice as long as the whole Cenozoic.  During the
Mesozoic the world went from more continental than it has been at any other
time with terrestrial life (Pangaea, during the Triassic and Early Jurassic)
to one in which the continents were more flooded than at any point
post-Pangaea (e.g., the mid-Cretaceous).

Because such a diversity of plate configurations, sea level heights, global
albedos, etc., it is very dubious to characterize the whole of the Reign of
the Dinosaurs as being any one thing: humid vs. dry, mild vs. extreme, etc.
There is no evidence for extensive continental glaciers at any point in the
Late Triassic through the end of the Cretaceous, but other than that, there
were probably all sorts of various climates at any given spot at any given
time in the Mesozoic.

>When do the first external genitalia occur in the fossil record?

I don't know the paleoentomological literature that well, but fossil insect
genitalia are quite well studied.  Don't know when they first show up, though.

As most vertebrates have a G or PG rated sense of modesty (:-), external
genitalia are not widely distributed in Vertebrata.  Furthermore, even of
the forms with obvious external genitals, these are most made of soft tissue
( - place joke here - ), and so are unlikely to be preserved.

On the other, er..., hand..., some mammals possess a "baculum" (Lt., little
rod), also known as the os penis.  This structure DOES fossilize, as it is
indeed bone, but you'd have to check with the paleomammologist crowd as to
the oldest known baculum.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661