Evolution of body size in sloths and anteaters (Xenarthra, Pilosa): phylogeny, metabolism, diet and substrate preferences

TOLEDO N.; BARGO, M. S.; VIZCAÍNO, S.F.; DE IULIIS G.; PUJOS F.

EARTH AND ENVIRONMENTAL SCIENCE TRANSACTIONS OF THE ROYAL SOCIETY OF EDINBURGH

ROYAL SOC EDINBURGH

Lugar: Edinburgo; Año: 2017 p. 289 - 301

1755-6910

Pilosa include anteaters (Vermilingua) and sloths (Folivora). Modern tree sloths arerepresented by two genera, Bradypus and Choloepus (both around 4?6 kg), whereas the fossil recordis very diverse, with approximately 90 genera ranging in age from the Oligocene to the early Holocene.Fossil sloths include four main clades, Megalonychidae, Megatheriidae, Nothrotheriidae, and Mylodontidae,ranging in size from tens of kilograms to several tons. Modern Vermilingua are representedby three genera, Cyclopes, Tamandua and Myrmecophaga, with a size range from 0.25 kg to about30 kg, and their fossil record is scarce and fragmentary. The dependence of the body size on phylogeneticpattern of Pilosa is analysed here, according to current cladistic hypotheses. Orthonormaldecomposition analysis and Abouheif C-mean were performed. Statistics were significantly differentfrom the null-hypothesis, supporting the hypothesis that body size variation correlates with thephylogenetic pattern. Most of the correlation is concentrated within Vermilingua, and less withinMylodontidae, Megatheriidae, Nothrotheriidae and Megalonychidae. Influence of basal metabolicrate (BMR), dietary habits and substrate preference is discussed. In anteaters, specialised insectivoryis proposed as the primary constraint on body size evolution. In the case of sloths, mylodontids,megatheriids and nothrotheriids show increasing body size through time; whereas megalonychidsretain a wider diversity of sizes. Interplay between BMR and dietary habits appears to be the mainfactor in shaping evolution of sloth body size.