Recommended fossil calibrators for time-scaled molecular phylogenies of Afrotheria

A phylogenetic framework provides the necessary evolutionary context for
studies of comparative anatomy, life history, behavior, biogeography,
systematics, and conservation. Time-scaled phylogenetic analyses require
researchers to include calibration ages which are used to fit a model that
transforms tree branch lengths into units of time. The inclusion of
multiple calibration ages (if they are available) is a best practice that
brings all the available evidence to bear on the temporal model. While
selecting the appropriate ages of calibrating fossil taxa is obviously
important, perhaps more relevant is where those calibrations are applied
in the tree. A misattributed fossil calibrator (e.g., using a stem-taxon
to set a minimum age on a tipward crown-node) can severely distort the
results. Our aim is to provide a summary of fossil calibrators that can be
used in molecular phylogenetic assessments of Afrotheria. The literature
that documents these fossils, and discusses their ages and affiliations,
is somewhat scattered. Included in this contribution are the oldest
extinct species that are (in our opinion) securely attributable to stem
lineages of afrotherian clades. Each informs a minimum age for the
adjacent rootward tree node. We then assemble a large DNA supermatrix that
includes 32 genes and 39 afrotherian genera – including recently extinct
elephants and sea-cows. A time-scaled phylogenetic estimate is derived
from this dataset with explicit inclusion of fossil taxa in the analysis.