The Evolution of Maximum Body Size of Terrestrial Mammals

Smith, Felisa A.; Boyer, Alison G.; Brown, James H.; Costa, Daniel P.; Dayan, Tamar; Ernest, S. K. Morgan; Evans, Alistair R.; Fortelius, Mikael; Gittleman, John L.; Hamilton, Marcus J.; Harding, Larisa E.; Lintulaakso, Kari; Lyons, S. Kathleen; McCain, Christy M.; Okie, Jordan G.; Saarinen, Juha; Sibly, Richard M.; Stephens, Patrick R.; Theodor, Jessica M.; Uhen, Mark D.

doi:10.1126/science.1194830

Cited by 263 publications

(301 citation statements)

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“…The upper boundary for feasible dinosaur physiologies is set by full endothermy, though the maximum size for a fully endothermic dinosaur is likely to have been well below the maximum size attained by some dinosaur lineages. The fossil record of herbivorous mammals shows a steady increase in maximum body size through the Cenozoic, to a maximum of ~ 17 tonnes in the early Oligocene Indricotherium and again in several Miocene species of Deinotherium (Smith et al 2010). Mammalian carnivores show a similar trajectory but the maximum size attained is much less (~1 tonne).…”

Section: Discussionmentioning

confidence: 83%

“…Mammalian carnivores show a similar trajectory but the maximum size attained is much less (~1 tonne). Whilst the configuration of the digestive system may constrain maximum size in mammalian herbivores (Clauss et al 2003), it seems likely that the ultimate constraint on body size is set by the need to lose the heat generated by their metabolism (Smith et al 2010;. The lower maximum size of carnivores may be set by physiological and ecological constraints on the ability to capture resources (Carbone et al 2007).…”

Section: Discussionmentioning

confidence: 99%

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Dinosaur Energetics: Setting the Bounds on Feasible Physiologies and Ecologies

Clarke

2013

The American Naturalist

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The metabolic status of dinosaurs has long been debated but remains unresolved as no consistent picture has yet emerged from a range of anatomical and isotopic evidence. Quantitative analysis of dinosaur energetics, based on general principles applicable to all vertebrates, shows that many features of dinosaur lifestyle are compatible with a physiology similar to that of extant lizards, scaled up to dinosaur body masses and temperatures. Sufficient metabolic scope would have been available to support observed dinosaur growth rates and allow considerable locomotor activity, perhaps even migration. Since at least one dinosaur lineage evolved true endothermy, this analysis emphasises that there was no single dinosaur physiology. Many small theropods were insulated with feathers and appear to have been partial or full endotherms. Uninsulated small taxa, and all juveniles, would presumably have been ectothermic, with consequent diurnal and seasonal variations in body temperature. In larger taxa inertial homeothermy would have resulted in warm and stable body temperatures, but with a basal metabolism significantly below that of living mammals or birds of the same size. It would appear that dinosaurs exhibited a range of metabolic levels to match the broad spectrum of ecological niches they occupied.

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Section: Discussionmentioning

confidence: 83%

Section: Discussionmentioning

confidence: 99%

Dinosaur Energetics: Setting the Bounds on Feasible Physiologies and Ecologies

Clarke

2013

The American Naturalist

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“…The extinction of Triassic taxa and rise of Jurassic taxa were mediated by an externally imposed crisis (3), and cannot be interpreted as a biotic replacement in which certain groups, say the Early Jurassic ichthyosaurs and plesiosaurs, demonstrated competitive superiority over their Triassic precursors. In this case, as with the initial rise of the dinosaurs (9) and the replacement of dinosaurs by mammals 65 Ma (26), external physical environmental factors were crucial. This confirms the need to assess carefully cases of purported competitive biotic replacements (27)(28)(29), and emphasizes the role of the Court Jester rather than the Red Queen in the larger patterns of macroevolution (30,31).…”

Section: Camentioning

confidence: 99%

Resetting the evolution of marine reptiles at the Triassic-Jurassic boundary

Thorne

Ruta

Benton

2011

Proc. Natl. Acad. Sci. U.S.A.

104

133

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Ichthyosaurs were important marine predators in the Early Jurassic,\ud and an abundant and diverse component of Mesozoic marine\ud ecosystems. Despite their ecological importance, however, the\ud Early Jurassic species represent a reduced remnant of their former\ud significance in the Triassic. Ichthyosaurs passed through an evolutionary\ud bottleneck at, or close to, the Triassic-Jurassic boundary,\ud which reduced their diversity to as few as three or four lineages.\ud Diversity bounced back to some extent in the aftermath of the\ud end-Triassic mass extinction, but disparity remained at less than\ud one-tenth of pre-extinction levels, and never recovered. The group\ud remained at low diversity and disparity for its final 100 Myr. The\ud end-Triassic mass extinction had a previously unsuspected profound\ud effect in resetting the evolution of apex marine predators\ud of the Mesozoic

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“…Usefully, it seems that mammals have not reached those limits; even the largest ever-known terrestrial mammals (36,37) fall well below the proposed maximum masses for terrestrial animals of between 20,000 to 1 million kg (38,39). If extant mammals had reached their maxima, it would be reflected in additional parameters (quadratic effects) in our model that would account for a slowing of the trajectory toward increasing size; however, at least for now, quadratic models are not necessary (SI Text).…”

Section: A B C Dmentioning

confidence: 99%

Adaptive evolution toward larger size in mammals

Baker

Meade

Pagel

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

119

151

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The notion that large body size confers some intrinsic advantage to biological species has been debated for centuries. Using a phylogenetic statistical approach that allows the rate of body size evolution to vary across a phylogeny, we find a long-term directional bias toward increasing size in the mammals. This pattern holds separately in 10 of 11 orders for which sufficient data are available and arises from a tendency for accelerated rates of evolution to produce increases, but not decreases, in size. On a branch-bybranch basis, increases in body size have been more than twice as likely as decreases, yielding what amounts to millions and millions of years of rapid and repeated increases in size away from the small ancestral mammal. These results are the first evidence, to our knowledge, from extant species that are compatible with Cope's rule: the pattern of body size increase through time observed in the mammalian fossil record. We show that this pattern is unlikely to be explained by several nonadaptive mechanisms for increasing size and most likely represents repeated responses to new selective circumstances. By demonstrating that it is possible to uncover ancient evolutionary trends from a combination of a phylogeny and appropriate statistical models, we illustrate how data from extant species can complement paleontological accounts of evolutionary history, opening up new avenues of investigation for both. macroevolution | adaptive evolution | evolutionary trends | Cope's rule | ancestral state reconstruction T he idea that large size confers some intrinsic advantage has lingered in the psyche of biologists for centuries. Researchers have proposed that bigger body sizes can increase tolerance to environmental extremes (1), reduce mortality (2), and enhance predation success (3), among other advantages. In support of these conjectures, analyses from a range of different taxonomic groups demonstrate that larger individuals within populations have significantly enhanced survival, fecundity, and mating success (4, 5). If these advantages are general and have played out over long time scales, they could explain the existence of Cope's rule (6): a broad trend toward increasing size through time (4, 5, 7).Mammals evolved from a relatively small common ancestor over 165 Ma (8-10) and went on to form one of the largest and most successful vertebrate radiations in Earth's history. Mammals vary greatly in size, spanning almost eight orders of magnitude. This variation implies that some groups have experienced much greater evolutionary change in size from the ancestral form than others. Indeed, the mammalian fossil record provides the clearest evidence in support of Cope's rule over long evolutionary time scales (6,11,12).Despite the paleontological support, evidence for Cope's rule remains elusive from studies of extant data alone (13-15), including studies of the mammals (16). A possible reason for the discrepancy between paleontological and extant data might be that conventional comparative methods for studying tr...

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The Evolution of Maximum Body Size of Terrestrial Mammals

Cited by 263 publications

References 27 publications

Dinosaur Energetics: Setting the Bounds on Feasible Physiologies and Ecologies

Dinosaur Energetics: Setting the Bounds on Feasible Physiologies and Ecologies

Resetting the evolution of marine reptiles at the Triassic-Jurassic boundary

Adaptive evolution toward larger size in mammals

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