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Resources, energetics and dinosaur maximal size


Proc Natl Acad Sci U S A. 2009 Jul 21;106(29):12184-8. Epub 2009 Jul 6
Resources and energetics determined dinosaur maximal size.
McNab BK.
Department of Zoology, University of Florida, Gainesville, FL 32611, USA. 
Some dinosaurs reached masses that were approximately 8 times those of the 
largest, ecologically equivalent terrestrial mammals. The factors most 
responsible for setting the maximal body size of vertebrates are resource 
quality and quantity, as modified by the mobility of the consumer, and the 
vertebrate's rate of energy expenditure. If the food intake of the largest 
herbivorous mammals defines the maximal rate at which plant resources can be 
consumed in terrestrial environments and if that limit applied to dinosaurs, 
then the large size of sauropods occurred because they expended energy in the 
field at rates extrapolated from those of varanid lizards, which are 
approximately 22% of the rates in mammals and 3.6 times the rates of other 
lizards of equal size. Of 2 species having the same energy income, the species 
that uses the most energy for mass-independent maintenance of necessity has a 
smaller size. The larger mass found in some marine mammals reflects a greater 
resource abundance in marine environments. The presumptively low energy 
expenditures of dinosaurs potentially permitted Mesozoic communities to support 
dinosaur biomasses that were up to 5 times those found in mammalian herbivores 
in Africa today. The maximal size of predatory theropods was approximately 8 
tons, which if it reflected the maximal capacity to consume vertebrates in 
terrestrial environments, corresponds in predatory mammals to a maximal mass 
less than a ton, which is what is observed. Some coelurosaurs may have evolved 
endothermy in association with the evolution of feathered insulation and a 
small mass.
One apparent caveat... some coelurosaurs did reach 8 tons... :-)
Guy Leahy