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Evidence for true endothermy in dinosaurs from comparing crocodiles and mammals



From: Ben Creisler
bcreisler@gmail.com

A new paper in PLoS ONE:

Roger S. Seymour (2013)
Maximal Aerobic and Anaerobic Power Generation in Large Crocodiles
versus Mammals: Implications for Dinosaur Gigantothermy.
PLoS ONE 8(7): e69361.
doi:10.1371/journal.pone.0069361
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0069361



Inertial homeothermy, the maintenance of a relatively constant body
temperature that occurs simply because of large size, is often applied
to large dinosaurs. Moreover, biophysical modelling and actual
measurements show that large crocodiles can behaviourally achieve body
temperatures above 30°C. Therefore it is possible that some dinosaurs
could achieve high and stable body temperatures without the high
energy cost of typical endotherms. However it is not known whether an
ectothermic dinosaur could produce the equivalent amount of muscular
power as an endothermic one. To address this question, this study
analyses maximal power output from measured aerobic and anaerobic
metabolism in burst exercising estuarine crocodiles, Crocodylus
porosus, weighing up to 200 kg. These results are compared with
similar data from endothermic mammals. A 1 kg crocodile at 30°C
produces about 16 watts from aerobic and anaerobic energy sources
during the first 10% of exhaustive activity, which is 57% of that
expected for a similarly sized mammal. A 200 kg crocodile produces
about 400 watts, or only 14% of that for a mammal. Phosphocreatine is
a minor energy source, used only in the first seconds of exercise and
of similar concentrations in reptiles and mammals. Ectothermic
crocodiles lack not only the absolute power for exercise, but also the
endurance, that are evident in endothermic mammals. Despite the
ability to achieve high and fairly constant body temperatures,
therefore, large, ectothermic, crocodile-like dinosaurs would have
been competitively inferior to endothermic, mammal-like dinosaurs with
high aerobic power. Endothermy in dinosaurs is likely to explain their
dominance over mammals in terrestrial ecosystems throughout the
Mesozoic.