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. 2001 Dec 4;98(25):14518-23.
doi: 10.1073/pnas.251548698. Epub 2001 Nov 27.

Dinosaurs, Dragons, and Dwarfs: The Evolution of Maximal Body Size

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Dinosaurs, Dragons, and Dwarfs: The Evolution of Maximal Body Size

G P Burness et al. Proc Natl Acad Sci U S A. .
Free PMC article

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.

Figures

Figure 1
Figure 1
(A) Body masses of top endothermic and ectothermic carnivores and herbivores, as a function of Holocene area of landmass inhabited. Separate regression lines are fitted through the points for each set of species except for ectothermic herbivores, which were not fitted because we have only three data points. Slopes of the lines are 0.47–0.52 and do not differ significantly between the species sets (P > 0.60). Note that larger landmasses support larger top species, and that, for a given area of landmass, body masses decrease in the sequence: ectothermic herbivore (○) > endothermic herbivore (●) > ectothermic carnivore (▿) > endothermic carnivore (▾). The two deviant points (●) at 3,200 kg, 8,259 km2 and at 1,150 kg, 209 km2 are the Crete dwarf elephant and the Santa Rosa dwarf mammoth, respectively, discussed in the text. Dinosaurs and early mammals are coded separately and discussed in the text. (B) Daily food requirements [grams of dry matter intake (GMI) per day] of top species (coded by the same symbols as in A), as a function of Holocene area of landmass inhabited. Because of an ectotherm's lower metabolic rate per gram of body mass, its food requirements are lower than those of an endotherm of the same body mass. As a result, B shows that an ectothermic top carnivore (▿, reptile) has the same food requirements (P > 0.10) as a endothermic top carnivore (▾, mammal or bird) on a landmass of the same area (and similarly for herbivores, ● vs. ○), although A showed that the ectotherm had the larger body mass. The two lines have the same slope (P = 0.57).

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