[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Physiological Adaptations of the Dinosauria (long)

> until John Ruben, a physiologist
> working at the University of Oregon in 1996, scanned several dinosaur
> skulls and showed that they lacked any trace of scroll-shaped bones (or
> cartilages) in their nasal cavities known as respiratory turbinates.

Ruben's papers have been far overestimated in their significance. As you
write below, e. g. the enormous noses of ceratopsians can have had the
functions of respiratory turbinates.

BTW, of course the skulls lacked any trace of cartilage because cartilage
just doesn't fossilize. Ruben claims to have shown that the nasal cavities
were too small to have housed respiratory turbinates, but even this is
debatable, and I'm sure it has been debated at length onlist.

> He concluded that dinosaurs could not have been endothermic, and suggested
> that they were instead "turbo-charged" reptiles with a high lung
ventilation rate.

A high ventilation rate means a high output of water which has to be
regained... and it is a prerequisite for endothermy...

> This discovery cast doubt on the dinosaurian ancestry of birds,

To shortly summarize the discussions -- Nonsense. Crocodiles,
prolacertiforms etc. don't have respiratory turbinates "either".

> and studies of bone material indicating endothermy (oxygen isotope
> ratios, well-vascularized bone, upright posture).

The other way round, IMHO...

> However, new genera of dinosaurs
> unearthed in China's Liaoning Province, showed that many small theropod
> dinosaurs possessed a coat of feathers or hair-like filaments. One of the
> most intriguing fossils was Sinosauropteryx prima, a compsognathid, which
> is a primitive coelurosaurian dinosaur, a group including Tyrannosaurus
> Feathers in such a large and diverse group as the coelurosaurs indicated
> that they were endothermic, using them as insulation like a modern bird.
> While not direct confirmation that they were warm-blooded,

Oh sure this is direct confirmation. Ectotherms aren't insulated because
they can only regulate their body temperature by exchanging warmth with
their surroundings, which any insulation would impede.

Acknowledgements for Ruben that he didn't buy the fairytale of the internal
collagen fibers!

> it did lend some credence to the hypothesis.

We can say that comes nearly as close to a proof of this hypothesis as
anything can in a natural science.

> These mixed messages from the fossil record
> provoked many paleontologists to view dinosaurs as heterothermic (both
warm and cold blooded at different times)

Erm... why? Why not simply endothermic? Today, heterothermy, if I have
correctly understood it, is an adaptation of very small endotherms (bats,
hummingbirds) for saving energy at times when they can't eat (when they
sleep). Probably hibernation is also called heterothermy.

> or possibly gigantothermic, using
> their immense size to store accumulated body heat.

For gigantothermy, one needs either a very compact body shape and AFAIK lots
of fat (the way of the leatherback turtle, the only known gigantotherm) or,
considering dinosaur proportions, great size, maybe starting at elephant
size or above. Look at sauropods, the dinosaurs that should be the most
likely gigantotherms: They have long necks and tails, air sacs en masse
(kind of contradiction...) and relatively longer legs than elephants. These
are interpreted as adaptations for surface enlargement and thus cooling.
Gigantotherms should be expected to have opposite adaptations to stay cool
by bulk.

> Personally, I didn't see why they couldn't have been endothermic with a
different system of
> moisture recovery.

Bingo IMHO :-)

> The alternative I propose is the antorbital fenestra


> Thus, the fossa functioned as a simple condenser,
> analogous to the respiratory turbinates of modern endotherms.

Hey! Good idea, and new at that AFAIK!

> Other structures found in dinosaurs could have also performed similarly,
such as
> the crests in lambeosaurines like Corythosaurus casuarius, the enlarged
> narial openings in ceratopsians, and the long necks and large external
> nares in many sauropods.

This fits the observation (forgot the ref now, probably Currie's and
Padian's _Encyclopedia of Dinosaurs_) that in theropods (except birds) there
was a trend to enlarge the antorbital fenestra, whereas in ?all other
archosaurs there was a trend to reduce its size.

> The difficulty in testing this hypothesis is mainly due
> to not knowing enough about predicted metabolic rates in dinosaurs, and
> not having the proper equipment to test the idea.

Still true.

> One way to go about it is to
> take samples of bone from animals like "Dilophosaurus" sinensis, and
> them to oxygen istopic studies. Knowing the approximate difference in
> temperatures between the crests and the bone lining the antorbital fossa
> would give some clues to the heat dissipation rate. The paleoclimatology
> the Early Jurassic would also be a crucial piece in the puzzle.

Why do you mention *"Dilophosaurus" sinensis*?

> While this has the potential to solve many questions about the
> physiology of dinosaurs, it may also explain their extinction.

Let me doubt that...

> Since this system relies on the
> ambient air temperature being somewhat lower than the animal's core body
> temperature, it would likewise be drastically impaired by a global
> increase in temperature.

Well, there were several temperature fluctuations in the Mesozoic; in the
Maastrichtian (not at its end) average temperatures rose by 3 °C (forgot the
ref :-( ), what seemingly didn't affect dinosaurs, and then the meteorite

Mantra time: Could a rise in temperature (or its cause, or its effects, or
whatever) explain THE WHOLE K-T extinction?

> Mammals, birds, and reptiles are oblivious to such factors.

While reptiles are (and birds can at least withstand higher air temperatures
because their body temperatures are tremendous), mammals get into real
trouble when their surroundings are warmer than them. (I'm not talking of
sauna conditions, where e. g. you can't lose water and the time is limited.)

If I haven't presented something correctly...

[HP] G. S. Paul & G. D. Leahy: Terramegathermy in the Time of the Titans:
Restoring the Metabolics of Colossal Dinosaurs, p. 177 -- 198 in the
Dinofest 1994 volume.
Argues that all dinosaurs, especially the biggest ones, were forced to have
been fully endothermic.

> Reptiles would bask in such warmth,

For a short time. Then they'd desperately look for a cool place.

> and both bird's and mammal's respiratory
> turbinates would function in spite of the changes.

Hm. They would probably, but they have no cooling effect...

> If, as suspected, some
> dinosaurs migrated, they may have been doing so to reach cooler climates
> where they could better survive the hot summer months during much of the
> Mesozoic.

In fact, the South Pole was dry land at the K-T boundary, and Alaska reached
as far north as 85°. This, IMHO, casts severe doubt on the speculation that
all non-avian dinosaurs died out because of a global increase in

> Many dinosaurs from the southern hemisphere (e.g. Amargasaurus
> caz[a]ui, Spinosaurus aegyptiacus, Ouranosaurus nigeriensis) have dorsal

All from equatorial regions (which is actually irrelevant to your argument,
it even supports it...).

Question -- Did *Spinosaurus* live in the southern hemisphere? Today, North
Africa is around 30° north...

> Perhaps a gradual increase of temperature
> due to volcanic greenhouse gases during the Late
> Cretaceous caused the slow decline of the dinosaur.

AFAIK, there was no significant increase in temperature, and the K-T
extinction was (mantra) NOT gradual!

> Further testing is
> required to validate my suspicions, but I hope that two of the most
> fascinating and controversial theories in dinosaur palaeontology have been
> resolved.

One may be in part!

> Any comments? [...] thanks in advance!