Search

Identifying ecomorphological convergence examples is a central focus in evolutionary biology. In xenarthrans, slow arboreality independently arose at least three times, in the two genera of 'tree sloths', Bradypus and Choloepus, and the silky anteater, Cyclopes. This specialized locomotor ecology is expectedly reflected by distinctive morpho-functional convergences. Cyclopes, although sharing several ecological features with 'tree sloths', do not fully mirror the latter in their outstandingly similar suspensory slow arboreal locomotion. We hypothesized that the morphology of Cyclopes is closer to 'tree sloths' than to anteaters, but yet distinct, entailing that slow arboreal xenarthrans evolved through 'incomplete' convergence. In a multivariate trait space, slow arboreal xenarthrans are hence expected to depart from their sister taxa evolving toward the same area, but not showing extensive phenotypical overlap, due to the distinct position of Cyclopes. Conversely, a pattern of 'complete' convergence (i.e., widely overlapping morphologies) is hypothesized for 'tree sloths'. Through phylogenetic comparative methods, we quantified humeral and femoral convergence in slow arboreal xenarthrans, including a sample of extant and extinct non-slow arboreal xenarthrans. Through 3D geometric morphometrics, cross-sectional properties (CSP) and trabecular architecture, we integratively quantified external shape, diaphyseal anatomy and internal epiphyseal structure. Several traits converged in slow arboreal xenarthrans, especially those pertaining to CSP. Phylomorphospaces and quantitative convergence analyses substantiated the expected patterns of 'incomplete' and 'complete' convergence for slow arboreal xenarthrans and 'tree sloths', respectively. This work, highlighting previously unidentified convergence patterns, emphasizes the value of an integrative multi-pronged quantitative approach to cope with complex mechanisms underlying ecomorphological convergence. [ABSTRACT FROM AUTHOR]

Convergent evolution is a major topic in evolutionary biology. Low bone cortical compactness (CC, a measure of porosity of cortical bone) in the extant genera of "tree sloths," has been linked to their convergent slow arboreal ecology. This proposed relationship of low CC with a slow arboreal lifestyle suggests potential convergent evolution of this trait in other slow arboreal mammals. Femoral and humeral CC were analyzed in "tree sloths," lorisids, koala, and extinct palaeopropithecids and Megaladapis, in comparison to closely related but ecologically distinct taxa, in a phylogenetic framework. Low CC in "tree sloths" is unparalleled by any analyzed clade and the high CC in extinct sloths suggests the recent convergence of low CC in "tree sloths." A tendency for low CC was found in Palaeopropithecus and Megaladapis. However, lorisids and the koala yielded unexpected CC patterns, preventing the recognition of a straightforward convergence of low CC in slow arboreal mammals. This study uncovers a complex relationship between CC and convergent evolution of slow arboreality, highlighting the multifactorial specificity of bone microstructure. [ABSTRACT FROM AUTHOR]