RE: Endothermy speculation

["Thomas R. Holtz, Jr." <th81@umail.umd.edu>]

At 11:57 AM 7/15/99 -0500, 2nd technician val the skeptic wrote:
>Pardon me, I've lurked for awhile and i can't help but have several
>questions about this issue.
>
>       [*]  > but we do find dinosaurs distributed worldwide, 
>> and some within the Antarctic circle, which at the very least would have 
>> been six months of darkness followed by six months of light.
>       [*]  
>could I have some references, please?  I'm mainly wondering what continent
>and in what time period these dinos have been found.  I've heard of
>specimens in all continents, but the time in which they lived on that
>continent is more an indicator of the climate and seasons than the continent
>itself, imho, as these continents haven't always been in the same place.
>I'm not a scientist, so I don't know where to find good references.

Dinosaurs have been documented now from every continent in the Triassic, and
in every continent in the Late Cretaceous, so the simplest explanation was
that they were everywhere from the Late Triassic onward.

Yes, there has been much movements of the continents since the Mesozoic.
However, if you check out some recent paleogeographic reconstructions (e.g.,
Smith et al. 1994, also found in Molnar's biogeography chapter in The
Complete Dinosaur) that half or more of Antarctica was 60 degrees S latitude
since the Late Jurassic, and almost the whole continent for the Early
Cretaceous onward.  Any Antarctic dinosaur was thus subject to tremendously
long nights and days, regardless of the average air temperature.

Smith, A. G., D. G. Smith & B. M. Funnell.  1994.  Atlas of Mesozoic and
Cenozoic Climates. Cambridge Univ. Press.

See also:
Rich, T. 1996. Significance of polar dinosaurs in Gondwana.  Mem. Queensland
Museum 39: 711-723.

>How does the presence of dinofuzz/feathers enter into the "endo/ecto"
>debate?   At what point did avian dinosaurs aquire full blown endothermy as
>they use it today?  Is it possible there was a different thermoregulatory
>system for theropods/birds than for other non-avian dinos?

Three excellent questions.  To be incredibly brief:
I) Dinofuzz on small coelurosaurs does counter earlier suggestions that the
apparent lack of insulation on small dinosaurs prevented them from being
endotherms.  (However, one could argue it doesn't necessitate the presence
of endothermy, but simply negates one previous counter argument to endothermy).

II) No one is certain: if we knew that the problem would be licked!!  Since
all living birds are fully endothermic as adults, their most recent common
ancestor was fully endothermic (under the simplest solution: otherwise, one
could argue it evolved independantly 9000 different times).  The closest
outgroup to birds for which we can directly measure physiology is
Crocodylia, and it is ectothermic.  So (and this is barring the possibility
that living crocodylians are secondarily ectothermic...) we can hypothesize
birds evolved endothermy sometime between the divergence of the croc lineage
and the bird lineage, and the time of the basal divergences within
Neornithes (living birds).  Anything more precise has to be based on
indirect evidence: hence the continued debate.

III) It is indeed quite possible.  People have developed various scenarios
for the adoption of endothermy (or aspects of endothermic metabolism) at
various points in the dinosaur tree.  However, as noted above, these are all
based on indirect evidence.

>thanks, and please don't flame me :-)

That's practically asking for it... :-)

                        Thomas R. Holtz, Jr.
                        Vertebrate Paleontologist
Deptartment of Geology                  Director, Earth, Life & Time Program
University of Maryland                  College Park Scholars
College Park, MD  20742       
Webpage: http://www.geol.umd.edu        Phone:301-405-4084
Email:tholtz@geol.umd.edu               Fax:  301-314-9661