Abstract
Most of life is extinct, so incorporating some fossil evidence into analyses of macroevolution is typically seen as necessary to understand the diversification of life and patterns of morphological evolution. Here we test the effects of inclusion of fossils in a study of the body size evolution of afrotherian mammals, a clade that includes the elephants, sea cows and elephant shrews. We find that the inclusion of fossil tips has little impact on analyses of body mass evolution; from a small ancestral size (approx. 100 g), there is a shift in rate and an increase in mass leading to the larger-bodied Paenungulata and Tubulidentata, regardless of whether fossils are included or excluded from analyses. For Afrotheria, the inclusion of fossils and morphological character data affect phylogenetic topology, but these differences have little impact upon patterns of body mass evolution and these body mass evolutionary patterns are consistent with the fossil record. The largest differences between our analyses result from the evolutionary model, not the addition of fossils. For some clades, extant-only analyses may be reliable to reconstruct body mass evolution, but the addition of fossils and careful model selection is likely to increase confidence and accuracy of reconstructed macroevolutionary patterns.
Highlights
Body mass evolution of Mammalia has received considerable attention in the literature [1,2,3,4,5,6,7,8,9,10,11]
A number of studies have argued that fossils are vital to understand patterns of body mass evolution [6,8,9,10], but results from analyses in Afrotheria are consistent if fossil tips are included or excluded from phylogenies
At least morphological character data, do have large impacts on the topology of Afrotherian phylogeny. These differences in topology do not have a large impact on analyses of body mass evolution in this study, but instead show how different data types and fossil inclusion can change our interpretations of evolution
Summary
Body mass evolution of Mammalia has received considerable attention in the literature [1,2,3,4,5,6,7,8,9,10,11]. We find the inclusion or exclusion of fossil tips has little impact on analyses of body mass macroevolution: with all phylogenies there is a relatively small ancestral body size for Afrotheria, and a branch-based shift in rate leading to Paenungulata and Tubulidentata. Tip dates for fossils were set as uniform distributions, with dates taken from the FossilWorks [43] portal, which accesses data in the Paleobiology Database [44] (see electronic supplementary material, S6). The fossilized birth–death model relaxes the assumption of a uniform prior between the timing of nodes and incorporates estimates of speciation, extinction and fossil sampling rates into the tree prior. Body mass data for extant species were predominantly taken from published estimates (see electronic supplementary material, S12). The values incorporate estimates for Late Cretaceous mammals from the fossil record (approximately 80 g [1]) as well as larger estimates for ancestral Afrotheria from genomic studies (approximately 0.5–30 kg; e.g. [4])
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