THE EFFECTS OF GEOGRAPHIC BINNING ON PHYLOGENETIC ANCESTRAL RANGE RECONSTRUCTIONS: EXAMPLES FROM THE LATE CRETACEOUS OF NORTH AMERICA

Ancestral range reconstructions have become an integral part of studying the evolutionary biogeography of various clades. Several methods have been devised to investigate geographic range evolution using parsimony, maximum likelihood, or a combination of both. Those methods use the distributions of terminal taxa to reconstruct ancestral ranges along interior branches of a phylogeny. Those reconstructions are powerful tools for understanding the evolutionary biogeography of a clade and how the resultant patterns may relate to broader dynamics within the earth system. However, the effects of using different resolutions of geographic bins have not been explored. The paleogeographic ranges of fossil taxa may be binned by the basin(s), region, or continent in which they inhabited. When investigating a clade’s historical biogeography, are the reconstructed patterns different when the taxa are geographically binned at different resolutions? Using dispersal-extinction-cladogenesis analysis, I reconstructed the ancestral ranges of four Late Cretaceous terrestrial vertebrate clades (Baenidae, Tyrannosauroidea, Chasmosaurinae, and Centrosaurinae). Taxa found in Upper Cretaceous basins across western North America (Laramidia) offer an excellent study system because individual depocenters are distinguishable and there is a clear regional break between northern and southern Laramidian basins. I altered the resolution at which terminal taxa of these clades were geographically binned: first by sedimentary basin and then regionally. I found that three of the four phylogenies analyzed produced congruent results when regional and basin-scale areas were specified. The greatest amount of variation between analyses resulted from how the phylogenies were temporally calibrated (i.e. minimized branch lengths vs. averaged branch lengths). These findings indicate a need to vary branch lengths used for maximum likelihood analyses and subsample throughout the stratigraphic ranges of taxa to gain insights into multiple hypotheses of a clade’s geographic range evolution. My analyses also show key similarities and differences in the paleobiogeography of these four clades that may be indicative of physical and/or biological processes impacting vertebrate distributions during the Cretaceous.