Physiological Adaptations of the Dinosauria

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Hello fello dino enthusiasts, i'm new here, but i'm just going to jump right 
in with an article I wrote recently, and one which i'd like your thoughts 
on. Pardon the simplistic terminology, but anyway, here it is:

In 1969, John Ostrom, a paleontologist working at the Peabody Museum of 
Natural History, discovered the remains of a small carnivorous dinosaur 
known as Deinonychus antirrhopus. Its body was light and compact, with a 
5-inch-long claw on its second toe used for eviscerating its prey. Ostrom 
believed this small dinosaur was a close relative of birds, citing many 
characteristics it shared with the earlier forms, like Archaeopteryx 
lithographica. He hypothesized that the dinosaurs were endothermic (or 
warm-blooded) like their flying descendants. These two ideas became widely 
accepted over the next decade and a half 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. In both mammals and 
birds, these structures are used in heating air as it is inhaled, and 
recovering water from the air when exhaled. In birds, the middle and 
anterior turbinates perform this task, whereas the posterior turbinates are 
used in olfaction. They are critical for maintenance of a high metabolism 
where an organism would otherwise quickly lose water through respiration. He 
concluded that dinosaurs could not have been endothermic, and suggested that 
they were instead "turbo-charged" reptiles with a high lung ventilation 
rate. This discovery cast doubt on the dinosaurian ancestry of birds, and 
studies of bone material indicating endothermy (oxygen isotope ratios, 
well-vascularized bone, upright posture). 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 rex. 
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, it did lend some 
credence to the hypothesis. These mixed messages from the fossil record 
provoked many paleontologists to view dinosaurs as heterothermic (both warm 
and cold blooded at different times), or possibly gigantothermic, using 
their immense size to store accumulated body heat. Personally, I didn't see 
why they couldn't have been endothermic with a different system of moisture 
recovery. The alternative I propose is the antorbital fenestra, a 
window-like opening in front of the orbits and behind the external nares. 
This feature of the skull is not unique to dinosaurs, it is also present in 
primitive archosauriforms (e.g. Proterosuchus). Current thinking is that it 
served to lighten the skull, but I think it had an important participation 
in respiration. Cool air from the environment would enter through the 
nostrils and pass along the underside of the nasal bone, where it would 
reach the olfactory bulbs beneath the frontal bones. The nasal passage would 
then make a sharp curve and open into the dorsal region of the antorbital 
fenestra posteriorly. Above the nasal bone are vascular foramina for the 
superior nasal artery. Many dinosaurs had prominent crests on their snout, 
which may have helped cool the blood in this artery, where it would travel 
down to the lateral wall of the antorbital fossa. This cool air would be 
heated by the warm walls of the chamber, then pass into the throat via the 
choanae. Upon exhalation, the warm, moist air would rise up into the 
antorbital fossa and condense on the cooled surfaces, exiting through the 
nasal passage proper. Thus, the fossa functioned as a simple condenser, 
analogous to the respiratory turbinates of modern endotherms. 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. 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. One way to go about it is to 
take samples of bone from animals like "Dilophosaurus" sinensis, and subject 
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 of 
the Early Jurassic would also be a crucial piece in the puzzle. While this 
has the potential to solve many questions about the physiology of dinosaurs, 
it may also explain their extinction. 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. Mammals, birds, and reptiles are oblivious to such factors. 
Reptiles would bask in such warmth, and both bird's and mammal's respiratory 
turbinates would function in spite of the changes. 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. Many dinosaurs from the southern hemisphere (e.g. Amargasaurus 
cazui, Spinosaurus aegyptiacus, Ouranosaurus nigeriensis) have dorsal sails 
which would have boosted body temperature relative to air temperature if 
used as a thermoregulatory device, or enlarged antorbital fossae which would 
enhance the condensation rate (e.g. Carcharodontosaurus saharicus, 
Giganotosaurus carolinii, Abelisaurus comahuensis). Perhaps a gradual 
increase of temperature due to volcanic greenhouse gases during the Late 
Cretaceous caused the slow decline of the dinosaur. 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.


Any comments? Does it get your stamp of approval? thanks in advance!


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