IS PHYLOGENETIC PALEOBIOLOGY SCALABLE? A META-ANALYTIC PHYLOGENY OF CETACEANS AND IMPLICATIONS FOR MODELS OF BODY SIZE EVOLUTION (Invited Presentation)

Quantitative paleobiologists have long recognized the need for a phylogenetic perspective when testing hypotheses about tempo and mode in morphological evolution. The recent development of probabilistic models for inferring time-scaled phylogenies of fossil taxa and of flexible methods for modeling morphological evolution mean that phylogenetic tests of macroevolutionary questions are now more accessible than ever to paleobiologists. Yet, despite considerable promise and potential, phylogenetic paleobiology remains hampered by the critical issue of taxon sampling; phylogenetic methods are data-hungry, and require large trees for reliable model fitting and parameter estimation, which will always present a challenge for morphological phylogenetics. As a result, testing hypotheses about the evolution of morphological diversity in higher level clades, a key objective of quantitative paleobiology, has remained somewhat out of reach.

We here explore an approach to circumvent this barrier by using phylogenetic meta-analysis. Though based on supertree approaches, the analytic pipeline that we employ accommodates phylogenetic uncertainty inherent in both source studies and the resulting meta-analysis, facilitating macroevolutionary model fitting over a distribution of plausible phylogenetic scenarios. Furthermore, the use of weak or strong taxonomic scaffolds can increase taxonomic coverage relative to species sampled in source studies, potentially yielding “completely sampled” trees of fossil taxa.

Applying this approach to the mammalian infraorder Cetacea (whales, dolphins and relatives) yields phylogenies ranging in size from ~450 to ~650 taxa. Although analysis of an original character-taxon matrix remains ideal, our meta-trees are adequate replacements in macroevolutionary research. Despite slight differences in the relationships among extant taxa, data, simulated on a molecular phylogeny yield similar estimates of phylogenetic signal and model parameter estimates when fitted to our meta-tree topologies. More importantly, the breadth of sampling accomplished here allows us to generate novel and important insights into the tempo and mode of cetacean size evolution that cannot be obtained from molecular studies or from analyses based on isolated sub-clades.