Morphological disparity and evolutionary rates of cranial and postcranial characters in sloths (Mammalia, Pilosa, Folivora)

Sloth morphological evolution has been widely studied qualitatively, with comparative anatomy and morpho-functional approaches, or through quantitative assessments of morphological variation using morphometrics. Only recently, however, have folivoran morphological disparity and evolutionary rates begun to be evaluated using discrete character data. Nonetheless, patterns of morphological evolution in separate character partitions have not been investigated, neither the relative influence of, on the one hand, phylogeny, and on the other, dietary and locomotory adaptations of sloths. Here we evaluate those patterns using a phylomorphospace approach, quantifying morphological disparity and evolutionary rates, and investigating possible drivers of morphological evolution for cranial and postcranial characters in Folivora. The evolution of the morphology in those partitions is associated with distinct patterns of disparity among clades and ecological groups, even though the two partitions do not differ substantially in overall evolutionary tempo. Historical processes shaped the morphological evolution of sloths more consistently than ecological ones, although changes in postcranial characters also seem to be associated with locomotory adaptations, in which morphological convergences were much more common. We also discuss important methodological trade-offs in investigations of partitioned datasets mostly composed of fossil taxa.

Methods
DATA

Phylogenetic data (sloths_data.nex & sloths_tree.tre) was obtained from the published study of Casali et al. 2022 (doi.org/10.1093/zoolinnean/zlac092).

Classification of each tip and node into phylogenetic, ecological and convergence hypotheses' groups (sloths_info.csv) was obtained from the literature (see Supplementary Table S2 for a detailed account), or was defined for this study according to the results obtained estimating ancestral states and evaluating phylomorphospace patterns.

The 'ggphylomorpho' R fuction is available in GitHub (https://github.com/wabarr/ggphylomorpho, v.0.2), being modified for this study.

The data files are meant to be opened in the R programming environment with a custom R_script.R file.

SUPPLEMENTARY INFORMATION

Eigenvalues and eigenvectors resulting from Principal Coordinate Analyses are provided as Supplementary Information.