Functional morphology and paleoecology of Pilosa (Xenarthra, Mammalia) based on a two‐dimensional geometric Morphometrics study of the Humerus

Abstract

The relationship between humerus shape and the modes of exploring substrate among extinct and extant Pilosa (especially anteaters and ground sloths) were investigated here. We used geometric morphometrics and discriminant analyses to relate morphological patterns and their possible ecological categories. Our results suggest that plesiomorphic taxa such as Nothrotheriidae, most Megalonychidae and basal Megatheriidae tend to have more slender humerus, associated to generalist habitus (climbing, swimming and digging activities), and while Mylodontidae developed specialized digging habitus. Additionally, we inferred ground sloths which inhabited the Brazilian territory during the Quaternary likely occupied at least four different niches. Mammals display morphofunctional adaptations on the limbs which are reflected on their modes of substrate exploration. Herein, we analyzed the humerus morphology of ground sloths and anteaters. Our results suggest that most of the Pleistocene Mylodonts were fossorial taxa, while most of the Santacrucian sloths plus extant anteaters were semiarboreal or semiaquatic taxa. The Pleistocene Megatheriidae should be ambulatory.

Locomotory Adaptations in 3D Humerus Geometry of Xenarthra: Testing for Convergence

“…The rate of shape evolution in fossorial Xenarthrans is significantly smaller than in other species. Such fossorial habitus characterizes most Cingulata and is possibly plesiomorphic to the group (Vizcaíno and Milne, 2002;Milne et al, 2009;Marshall, 2018), although it is surprisingly present among giant ground sloths like Glossotherium (Bargo et al, 2000;Vizcaíno et al, 2001;de Oliveira and Santos, 2018). Conversely, arboreal species evolved at faster rates than in any other Xenarthra.…”

“…Other specialized diggers can be found also among Pilosa. Glossotherium robustum was demonstrated to be a specialized digger (Bargo et al, 2000;Vizcaíno et al, 2001;de Oliveira and Santos, 2018). On the contrary, other ground sloths were best adapted to a terrestrial lifestyle (Bargo et al, 2000;Vizcaíno et al, 2001;de Oliveira and Santos, 2018).…”

“…Glossotherium robustum was demonstrated to be a specialized digger (Bargo et al, 2000;Vizcaíno et al, 2001;de Oliveira and Santos, 2018). On the contrary, other ground sloths were best adapted to a terrestrial lifestyle (Bargo et al, 2000;Vizcaíno et al, 2001;de Oliveira and Santos, 2018). Extant sloths (Bradypus and Choloepus) are known as tree sloths for their strictly arboreal lifestyle (Montgomery, 1985;Chiarello, 2008;Toledo et al, 2012), as well as the anteaters (White, 2010), but the latter are capable of above branch locomotion (Nyakatura, 2011).…”

“…The humerus is a loadbearing postcranial element in quadrupedal mammals (Bertram and Biewener, 1992) and correlates quite strongly with body mass, locomotory, and habitat adaptations (Gingerich, 1990;Egi, 2001;Elton, 2002;Polly, 2007;Walmsley et al, 2012;Meloro et al, 2013;Elton et al, 2016;Botton-Divet et al, 2017). In Xenarthrans, the broad locomotory diversity well correlates with humerus functional morphology (Fariña and Vizcaíno, 1997;Toledo et al, 2012;de Oliveira and Santos, 2018).…”

Phylogenetic, Allometric, and Ecological Factors Affecting Morphological Variation in the Scapula and Humerus of Spiny Rats (Rodentia: Echimyidae)

“…It is important to consider that the phylogenetic component of morphological variation does not necessarily carry adaptive traits and may be the result of neutral evolution (Duret 2008;Kern and Hahn 2018). In addition, body size and/or bone structure size may also explain some variation in shape, because of evolutionarily conserved allometric constraints or structural rearrangements required to support body weight (Milne et al 2009;Campione and Evans 2012;Walmsley et al 2012;de Oliveira and Santos 2018). Therefore, attempts to identify locomotor adaptations should not disregard the possible existence of phylogenetic structuring and allometric effects on morphological variation.…”