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Re: [GSP1954@aol.com: Re: dinosaur endothermy (long)]



[Terry's not back, but I sent him Greg's message for comment. -- MR ]

The "evidence" for endothermy in dinosaurs given here (erect posture, bone
isotope concentration, bone histology) is not causally or functionally
linked with endothermy.  This statement, like my original one, is neither
"absurd" nor is it a "statement of unsubstantied belief".  

To look at only limb posture (in the interest of time)...Desmond (1975)
proposed that the sprawling limb posture was somehow "less efficient" than
erect limb posture.  Bakker (1971) argued that erect limb posture supposedly
increased the ability to forage, thereby increasing opportunity for food
consumption.  Since the energetic costs of endothermy are elevated compared
to those of ectothermy, there is a requisite increase in fuel consumption;
therefore, erect limb posture was proposed to be linked to endothermy.
However, as Bennett and Dalzell (1973) point out, if these statements were
true, one would expect a significant difference in the energetic cost of
locomotion between the two types of posture.  However, Taylor (1973)
demonstrated that the net cost of locomotion (the difference between active
and resting oxygen consumption rates divided by running velocity) in lizards
is less than or equal to that for equivalently sized mammals at the same
speed.  Therefore, there is currently no evidence that one type of posture
is more, or less, energetically costly than the other.  In other words,
there is no direct link between limb posture and metabolic rate.

Currently, the only evidence that is functionallly linked to metabolism in
extinct animals--including dinosaurs--is the presence or absence of nasal
respiratory turbinates.  Contrary to Greg Paul's opinion, the diameter of
the nasal passage proper of modern endotherms is approx. 4X larger than
those of modern ectotherms. The diameter nasal passage proper of dinosaurs
we have been able to measure is less than or equal to those of modern
ectotherms.  The smaller diameter of the resp. passage of ectotherms
precludes the presence of RTs as evidence by the fact that RTs are not found
in any living ectotherm.  RTs fucntion to increase surface area in the nasal
passage as well as reducing respiratory heat and water loss.  This is true
of endotherms that have reduced RTs (pigeons, humans, etc.) regardless of
the size of teh animal or teh environment in which it lives.  In the RARE
cases where endotherms lack RTs (>99% of endotherms possess RTs), there are
secondary modifications to deal with problems of resp. heat and water loss.

I would encourage those intereseted in such questions to read the available
information and decide for themselves.

TDJ
:-{)
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    Terry D. Jones                             Voice:  541/737-6120       |
    Oregon State University              Fax:      541/737-0501          
    Dept. of Zoology                         JONEST@bcc.orst.edu
    3029 Cordley Hall
    Corvallis, OR  97331-2914
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