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On Jimmy Durante and his turbinates
A recent posting brought up one of my favorite subjects these days, the
recent claims by Hillenius and Ruben that respiratory turbinals (RT, which I
will use as a shorthand for all nasal structures with respiratory epithelia)
are the first reliable means of estimating metabolic rates in dinosaurs and
other extinct animals. Here are some of the many reasons this is not true.
It has been asserted in some places that there is a "tight" correlation
between the absence versus presence of (RT) and ecto versus endothermy in
reptiles, birds, and mammals, and/or that ALL birds and mammals must have RT
in order to conserve water, etc.
Imagine my "surprise" when refering to Bang's 1971 (Acta Anatomica 79(suppl
58:1) classic study of bird noses when I found that gannets, cormorants and
pelicans not only lack RT, they have blocked external nares and breath
entirely through the mouth! Bang's discussion and figures show a number of
other birds with very reduced RT.
My coworker Guy Leahy has dredged up data on mammalian RT or the lack of
same, sources incl the classic V. Negus 1958 (Comp Anatomy of Vertebrates)
study. Elephants, whales, sirineans and some human children lack RT, and they
are poorly developed in saiga antelope, tapirs, bats, tree shrews and
primates (incl big snouted savanna baboons, Durante, Hillenius and Ruben).
(We suspect maxilloturbinals are small in rhinos, anyone with info please let
The reasons for the severe reduction and loss of RT in mammals and birds are
many and sometimes not well understood, but in any case it disproves a tight
correlation with metabolic rates. Yet only the the birds and mammals with
well developed RT get figured and discussed in detail in the papers by
Hillenius & Ruben. Not much detailed in the figures and text are the mammals
and birds with little or no RT, living in habitats from very wet to very dry,
that have high metabolic and breathing rates, yet somehow manage not to
shrivel up like prunes from dehydration. Rather odd.
In fact, the experimental protocal followed by Hillenius did not prove that
RT are responsible for water conservation, he merely showed that blocking the
nostrils of mammals with large RT increased their water loss. He failed to
show exactly what structure saves the water, and he failed to do the same
experiment on animals with small or no RT. It is known that rates of
respiratory water loss are similar in birds and mammals with poorly developed
or no RT (pigeons, penguins, whales, humans) as in those with well developed
RT (incl seals). All the fuss about dehydrating poor endotherms if they do
not have RT is amusing.
Nor do H & R discuss in detail the well demonstrated fact that in many
mammals (and perhaps in birds) RT are involved in brain cooling during
exercise and on hot days (see Baker Scientific Amer 1979 79(5):130). It is
possible that large complex RT are associated at least in part with brain
size, more than metabolic rate. It is also possible according to a number of
researchers, but less certain, that RT are associated with heat retention,
and indirectly with olfaction. RT probably help trap lots of the nasty
airborne stuff that would otherwise get into our lungs. Fact is that the full
function of RT is still poorly understood. In any case the dream of a tight,
simple correlation between RT and metabolism as presented by H & R is
misleading and inaccurate. Sorry Ruben, your paleometabolic Rosetta Stone is
more a cracked, dirt encrusted brick amid the rubble of failed hypotheses.
To take this point further, that a single character can be used to diagnose
the metabolics of an extinct animal is about as likely that a single
character can be used to determine the phylogenetic position of the same.
Animals are the sum of their parts, and restoring their metabolics probably
requires assessing their entire anatomy.
As for finding RT in dinosaurs, the big question is how can we ever hope to?
In the closest relatives of dinos, birds, the RT are usually entirely made of
cartilage, and often leave no bony trace of their existence. What if various
dinosaurs had cartilage RT, and they were not supported on bony ridges? You
can section and CT scan dino skulls until you turn blue and never find the
dang things. (Actually, ossified RT were reported by Maryanska in Asian
ankylosaurs [1977 Palaeontologica Polonica 37:85], whether this
identification is correct is not clear.)
So, let's say we have a dinosaur skull with no traces of RT. What do we now
know? We know that its respiratory capacity and metabolic rate may be like
that of a lizard, a cormorant, or an elephant. Now that tells us a lot! The
conclusion is the same if a dinosaur that has external nares too small for it
to breath through the nose (which appears true of pachycephalosaurs), or has
a nasal cavity too small to contain RT.
Now, it is true that RT are found only in birds and mammals, so their
presence can be taken as evidence, albeit rather weak, for rates of
respiration and metabolism higher than observed in reptiles.
Please note that most of what has been cited here has long been published in
the literature. It took me fifteen minutes of scaning Bang 1971 to see some
gaping holes in the RT hypothesis. This might leave one at something of a
loss for understanding why RT have become such a hot item for restoring
paleometabolics, when a number of birds and mammals do not have them. An
initially good, but in the end flawed, idea seems to have gotten out of hand
- kind of like one of those experiments in those 1950's B-movies. Hopefully
the RT monster can be nipped in the bud, and won't grow into the huge beast
that the big-dinosaurs-will-overheat-if- they-were-endotherms myth has
become. Like they say, it does not take a rocket scientist to see that RT are
not critical for high metabolic rates when there are birds that not only lack
RT, but that do not even bother to breath through the nose, while desert
elephants have no maxilloturbinals yet do not keel over from thirst!
(Rowe, please forward to JR, I sometimes have trouble getting AOL to send
stuff outside their system).