Dinosaurs, dragons, and dwarfs: The evolution of maximal body size
Abstract
Among local faunas, the maximum body size and taxonomic affiliation of the top terrestrial vertebrate vary greatly. Does this variation reflect how food requirements differ between trophic levels (herbivores vs. carnivores) and with taxonomic affiliation (mammals and birds vs. reptiles)? We gathered data on the body size and food requirements of the top terrestrial herbivores and carnivores, over the past 65,000 years, from oceanic islands and continents. The body mass of the top species was found to increase with increasing land area, with a slope similar to that of the relation between body mass and home range area, suggesting that maximum body size is determined by the number of home ranges that can fit into a given land area. For a given land area, the body size of the top species decreased in the sequence: ectothermic herbivore > endothermic herbivore > ectothermic carnivore > endothermic carnivore. When we converted body mass to food requirements, the food consumption of a top herbivore was about 8 times that of a top carnivore, in accord with the factor expected from the trophic pyramid. Although top ectotherms were heavier than top endotherms at a given trophic level, lower metabolic rates per gram of body mass in ectotherms resulted in endotherms and ectotherms having the same food consumption. These patterns explain the size of the largest-ever extinct mammal, but the size of the largest dinosaurs exceeds that predicted from land areas and remains unexplained.
Acknowledgments
For providing us with unpublished data, we thank Per Christiansen, Bob Dewer, Helen James, Ben Kear, Doug Kelt, Ross MacPhee, Cecile Mourer-Chauviré, Ralph Molnar, Patrick Nunn, Maria Rita Palombo, Greg Paul, Dave Steadman, Alan Tennyson, John Thorbjarnarson, Gerard Willemsen, Paul Willis, and Trevor Worthy. We thank Bob Hill for pointing out the relevance of Cretaceous atmospheric CO2 levels. Funding was provided by the Natural Sciences and Engineering Research Council (Canada).
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Copyright © 2001, The National Academy of Sciences.
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Accepted: October 15, 2001
Published online: November 27, 2001
Published in issue: December 4, 2001
Acknowledgments
For providing us with unpublished data, we thank Per Christiansen, Bob Dewer, Helen James, Ben Kear, Doug Kelt, Ross MacPhee, Cecile Mourer-Chauviré, Ralph Molnar, Patrick Nunn, Maria Rita Palombo, Greg Paul, Dave Steadman, Alan Tennyson, John Thorbjarnarson, Gerard Willemsen, Paul Willis, and Trevor Worthy. We thank Bob Hill for pointing out the relevance of Cretaceous atmospheric CO2 levels. Funding was provided by the Natural Sciences and Engineering Research Council (Canada).
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