The evolution of placental mammal body sizes: evolutionary history, form, and function

Abstract

The unimodal, right-skewed distribution, most frequently identified in contemporary descriptions of placental mammal body size distributions, masks an underlying multidistribution structure; a long-term evolutionary process that has generated a concatenation of two or three frequency distributions specific to locomotory modes (plantigrade, digitigrade and unguligrade). The Afrotropical assemblages are bimodal, with a tendency towards trimodality, whereas the Nearctic assemblage is unimodal. However, mixtures of two and three normal distributions fitted the Nearctic data well, suggesting a multidistribution structure masked by disproportionate species numbers within locomotory modes. Differences in proportional species numbers within modes between assemblages may reflect the evolutionary history of form and function. However, common interassemblage predictions of such proportions in contemporary distributions may be disguised by the relative severity of the Pleistocene megafaunal extinction (patterns supported by the fossil record), geographical scale, and taxonomic composition. A species gap occurs at body sizes around 1 kg at the interface between the largest plantigrade mammals and the smallest digitigrade mammals, coincident with the minimum interspecific variance of basal metabolic rate. In terms of the evolution of the optimal body size in the trade-off between mortality and production, there may be good historical and evolutionary reasons why we should not expect optimization to produce the same results in different zoogeographical assemblages. Moreover, the evolution of diverse mammalian forms and functions, especially with respect to predator-prey interactions and diet, render a single body size optimum untenable in the search for an energetic definition of fitness.

The evolution of micro-cursoriality in mammals

“…Nevertheless, these observations, as well as the observation of comparatively slow MRSs in plantigrade mammals smaller than 1 kg (Lovegrove, 2004), support several hypotheses on the relationship between the evolution of limb morphology and body size in mammals during the Cenozoic (Lovegrove, 2000;Lovegrove, 2001;Lovegrove, 2004;Lovegrove and Haines, 2004;Lovegrove, 2012b;Lovegrove and Mowoe, 2013). For example, the Bowtie model argued that, following the evolution of larger, faster digitigrade carnivores following the Eocene Thermal Maximum, most plantigrade mammals were constrained from evolving to body sizes larger than ~0.5 kg (Lovegrove, 2000;Lovegrove, 2001;Lovegrove and Mowoe, 2013).…”

Test of the Optimal Body Size Model for Strepsirhines

“…Incorporating vertical ranging data into home range estimates provides a more accurate measure of the distance traveled and energy expended by arboreal primates as well as the density of the resources within their arboreal environment (Milton and May, 1976). Moreover, body size tends to be constrained to moderate sizes in arboreal mammals, such as most of the strepsirhines tested here (Bakker and Kelt, 2000), because of the physical and energetic costs of living in the forest canopy (Lovegrove and Haines, 2004). For example, arboreal taxa must be small enough for tree branches to support their body masses (Emmons, 1995).…”

“…The last assumption may be particularly problematic because of primate sexual dimorphism and the annual variations in body size that occur in many Malagasy strepsirhines (Atsalis, 1999;Clutton-Brock, 1985;Ganzhorn and Schmid, 1998;Kappeler, 1991;Leutenegger and Cheverud, 1982;Plavcan and van Schaik, 1997;Smith and Cheverud, 2002). Some researchers have questioned the unimodal, right-skewed distribution that is inherent to the OBS model (Jones and Purvis, 1997;Kozlowski, 1996;Lovegrove and Haines, 2004). Lovegrove and Haines (2004) found that subdividing Afrotropical mammals-including primates-into specific locomotory modes-plantigrade, digitigrade, and unguligrade-resulted in a trimodal rather than unimodal pattern of body size distributions.…”

“…Some researchers have questioned the unimodal, right-skewed distribution that is inherent to the OBS model (Jones and Purvis, 1997;Kozlowski, 1996;Lovegrove and Haines, 2004). Lovegrove and Haines (2004) found that subdividing Afrotropical mammals-including primates-into specific locomotory modes-plantigrade, digitigrade, and unguligrade-resulted in a trimodal rather than unimodal pattern of body size distributions. Among empirical tests of the OBS model, Symonds' (1999) study of insectivores showed no relationship between body mass and life history variables after controlling for phylogeny.…”

Ecological and Phylogenetic Correlates to Body Size in the Indriidae

“…One of the most perplexing problems in primate evolutionary biology is understanding the relationship between body size and various ecological variables (Conroy, 2003;Gaston and Blackburn, 1996;Lovegrove and Haines, 2004). Interspecific allometry (IA) in adult body size is often linked to diet, particularly for folivores (Peters, 1986).…”