This is the best phylogeny that can be drawn for the artiodactyls as of June 1998. The tree is based on a review of about 300 recent scientific publications. Colored bars represent independent genetic markers that definitively partition artiodactyls.
Gray boxes show unresolved nodes where conflicting trees are still prevalent in the literature.
Species shown in red are suggested strategic candidates for prion gene sequencing. These sequences, if completed, would vastly improve our ability to reconstruct ancient phylogenetic nodes, our understanding of what constitutes the wild type allele in sheep and cattle, and our understanding of fixed mutational events during the evolution of this protein. In turn, this helps understand which protein domains are tightly conserved and which are random connecting loops of little normal function. For example, the complete absence of change in the pre-repeat region over 100 million years conflicts with a recent study asserting no fixed structural role for this domain. Molecular phylogeny based on aligning single genes gives erratic results, depending on assumptions, methodologies, and weighting schemes.