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RUBEN ET AL ON R.T.



I have yet to see a single comment on Ruben et al's paper, published in
_Science_ of August 30th. 

RUBEN, J.A., HILLENIUS, W.J., GEIST, N.R., LEITCH, A., JONES, T.D., CURRIE,
P.J., HORNER, J.R. and ESPE, G. 1996. The Metabolic Status of Some Late
Cretaceous Dinosaurs. _Science_ 273: 1204-7

Just about everyone is familiar with the arguments presented here:
that dinosaur nasal passages are simply not big enough in
cross-sectional area to allow the high lung-ventilation rates employed
by tachymetabolic tetrapods, nor do RT 'fit' into these
passages. _Nanotyrannus_, _Ornithomimus_, _Dromaeosaurus_ and
_Hypacrosaurus_ were analysed.

The inclusion of the hypacrosaur is interesting, as Horner has
previously (at the last SVP meeting) shown CAT scans of a hypacrosaur
skull, and used the images to suggest that RT _might_ have been
present. These images did not match expectations of what hypacrosaur
RT _might_ look like however, and I guess Horner's authorship in this
paper shows that he's changed his mind: p. 1207 says '..CAT scans from
a particularly well-preserved skull of... _Hypacrosaurus_...  show no
evidence of the presence of respiratory turbinates'.

Those who question the assumptions inherent to the association of RT with
elevated metabolism have pointed out that a number of extant tachymetabolic
tetrapods do not possess RT. It is well known that sulids, pelecanids and some
other seabird families lack RT entirely. However, they are clearly specialised
for plunge-diving and even lack external nares. In ref. note 6, Ruben et al.
state that 'anterior open nostrils would be a potential liability in such
cases'. 

RT are also poorly developed or absent in cetaceans: Ruben et
al. explain that 'the presence of compensatory mechanisms serves to
emphasize that endothermic lung ventilation rates necessitate some
adaptation in order to counteract loss of respiratory water or
heat'. The seabirds have big salt glands, and drink seawater, and some
cetaceans 'possess a specialized nasal-cavity air compression
mechanism for reduction of respiratory water and heat loss'.

But then, other animals, even humans on occasion, lack RT. However,
the case for non-tachymetabolic dinosaurs is looking better and
better. If this bothers you, learn more about extant reptiles. Did a
pile of good for me.

"But that was never a condition of our agreement, nor was giving Hann to this
bounty hunter!"

DARREN NAISH
dwn194@soton.ac.uk