As a graduate student, Mark became interested in the statistical basis of phylogenetic reconstruction. His work has focused on models and algorithms for Bayesian and maximum likelihood tree inference. In addition to developing and testing inference methods, members of the Holder lab contribute to a large number of open-source software packages for phylogenetics (for example NCL, Phycas, DendroPy, GARLI, beagle, SATé, and GELL).