GEOL 104 Dinosaurs: A Natural History
Fall Semester 2006
Dinosaur Physiology roundup
Some ways in which dinosaurs are distinctly different from modern mammalian communities:
So, what is the answer to dinosaur physiology & ecology? We still don't know.
- Much higher rate or production: dozen eggs per year, independant of size vs. litter size
and gestation period scaled to body size
- From this, dinosaur populations could absorb many more fatalities and survive than
- Also, dinosaurs occupied many more niches in their lifetime than a mammal, because all
dinosaurs begin very small
Current status, and some scenarios:
We know that:
- Living dinosaurs (birds) are all endothermic tachymetabolic homeotherms
- The living sister group to dinosaurs, crocs, are all ectothermic bradymetabolic
- All groups of dinosaurs show upright stance and other adaptations suggesting active
- All large dinosaurs, and many small ones, show signs of having high breathing rates
- If P/P ratios are real, dinosaur ecologies were more similar to mammals than to basal
- Many dinosaurs (particularly Late Cretaceous forms) show very sophisticated feeding,
locomotory, and social adaptations
Scenario I: Bakker or "Hot-Blooded Dinosaurs" model
Dinosauria (and probably Ornithodira) were endothermic tachymetabolic homeotherms;
therapsids and pseudosuchians had intermediate rates (crocs would thus be a reversal).
Scenario II: Ruben or "Good Reptile" model
No dinosaur was warm-blooded, but at least some had means of rapidly oxygenating their
blood to be "turbo-charged" and thus function temporarily as highly active animals. True
endothermic tachymetabolic homeothermy doesn't appear until after Archaeopteryx.
Scenario III: an intermediate model ("Damn Good Reptile" model)
All dinosaurs had some degree of endothermic tachymetabolic homeothermy while young; small
dinosaurs retained this into adulthood. Large dinosaurs experienced a slow down in
metabolic rate, but still higher than any cold-blooded animal (~ 2/3 the rate of mammals
of same size). Efficient oxygenation of blood and gigantothermy allowed these dinosaurs
to be as active as mammals without the same energy costs.
- Benefit of model:
- Explains large amount of "meat on the hoof" in Mesozoic: a 4 ton hadrosaur with 2/3
mammal metabolism would only need as much food as a 800 kg bison.
- Thus, the higher capacity for dinosaur population growth would be realized
- Development of insulation in coelurosaurs suggest that they were fully endothermic
- Birds retain primitive condition of warm-blooded juveniles into adulthood
- Progressive variation: as Mesozoic continued, different groups of dinosaurs
(hadrosaurids, ceratopsids, coelurosaurs, maybe even titanosaurs and ankylosaurids)
independently developed full endothermy from the original Scenario III condition
Still much work to be done.
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Last modified: 14 July 2006