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A physiological query re: feathered theropods



R.D. Ohmart and R.C. Lasiewski, in a 1971 paper,
documented how the dinosaur Geococcyx conserves basal
metabolic energy by hypothermia and basking.
Endothermy requires, as one will recall, good
insulation and high metabolic rates (MRs). One can
infer that, late at night, with reduced ambient
temperature (Ta), and avoiding diurnal
theropod/pterosaur hunters, the small feathered
dinosaurs (whose body temperature may have been ~ 35C)
could not avoid a lowered MR, and entered torpor,
basking in afternoon light elevating MR and body
temperature (Tb), so they could be active for several
more hours after sundown. This basking may have been
passive (sitting in a tree), or active (going from a
hidden refuge to an area exposed to sunlight), and one
can assume a period of two hours required to raise the
core body temperature again. It makes logical sense to
see the feathered theropods as heterothermic: lowered
Ta and scarcity of food precipitating torpor (a
lowered Tb), but with thermoregulated Tb. Thus, unlike
Geococcyx, the roadrunner, which uses torpor to save
energy and then basks, the theropods may have required
basking because of a decreased MR.

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