RE: Insulation does not = "Warm-blooded"

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

Howdy, all.

I normally stay out of thermal ecology debates, because quite frankly I
think there are a lot of essential material that is not yet available by
which we could fairly evaluate different potential models.  (To put this
another way, there's a lot of work that needs to be done on extant forms
before we can more fully understand the extinct).

However, I do have something to say about the following:

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> David Marjanovic
> >I
> > think that in popular imagination it does, but in reality a
> bradymetabolism
> > doesn't hinder any of the proposed lifestyles of dinosaurs, so
> I don't see
> why
> > the stereotypical reptilian activity levels should ever come into play.
>
> Why doesn't it hinder any of the proposed lifestyles of dinosaurs, such as
> migrating from Alberta to Alaska and back, galloping at 50 km/h, running
> bipedally at even higher speeds, ... according to P&L even
> growing to over 1
> tonne in the first place?

EEK!  The Gospel According to Bob! :-)

As pointed out by HP(h.D., soon) Bonnan and others, be VERY cautious about
most of the above propositions.  Some of these have been accepted as
certainty in dinosaur-fandom when in fact the data supporting them are less
substantial.  For example:

*Alberta-to-Alaska migration: in principle I don't have a problem with this
as such.  However, our present evidence does not demonstrate such
migrations.  It DOES demonstrate that the species range of some taxa goes
from Alberta-to-Alaska, but that doesn't mean that any one individual or
population would move from Alberta to Alaska seasonally, or even in a
lifetime.  _Puma concolor_'s species range is Alaska to Argentina, but no
cougar actually travels that whole distance.  Similarly, _Daspletosaurus_
(and probably _D. torosus_ itself) has an Alberta-to-New Mexico range, but
we don't know that a) an individual daspletosaur migrated from one end to
the other, or even b) if this entire range were occupied by _D. torosus_ at
any given time slice. {Theoretically, the southern part of the range might
have been occupied at one point, and as habitat shift occurred the species
moved north, or vice versa)}.

Now, I grant you, large-bodied polar dinosaurs would indeed have an
incentive to get south of the Polar Circle during the winter, but they
needn't move all the way to the southern end of their range in order to
survive.

*Galloping at 50 km/h, or running bipedally even faster: That would be very
cool, I admit, and in my heart-of-hearts I hope it is true.  Nevertheless,
this has NOT been demonstrated for any Mesozoic dinosaur.  Time to face the
facts (or the evidence, if you like): we have not good metric for
determining absolute values of speed for living taxa save for running them
in controlled circumstances.  This has been done for humans, horses, dogs,
cheetahs, and maybe a handful of other species.  We do not know the absolute
speeds of the vast majority of living ungulates and carnivorans and such:
the data in Walker's Mammals of the World and the like are guesstimates,
with very big uncertainties.  Given this, we do not yet have the data to
support particular predictive models of calculating speeds of living taxa,
for whom we know (or can find) the soft tissue masses and densities,
metabolic rates, tidal volume of lungs, etc.

It would be very nice if there were a formula that you could plunk some limb
dimensions and/or muscle mass dimensions and/or respiration rate dimensions
etc. into and figure out how fast a critter moved.  I've tried to develop
some before myself, actually, when I was younger and more naive.
Unfortunately, such calculations tend to be independant of the real world at
present, since we don't have the modern values to constrain it.

*Ectotherms incapable of growing over 1 tonne: Actually, this is an
interesting situation.  Fully terrestrial unquestioned ectotherms DO seem to
be limited in size: critters like _Megalania_ or the big tortoises or
pareiasaurs.  Some non-contraversial ectotherms do GREATLY exceed this size,
though: giant crocs, plesiosaurs, etc., but these are aquatic forms.  Does
make one wonder, though, if the limiting factor might include mechanical
support rather than physiology?  As above, more work needs to be done.

Later,

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796