Fig. 2.

The evolution of morphological placental features in mammals. Parsimony reconstructions of internal nodes are shown for three morphological features (see Materials and Methods for details of reconstruction methodology). Taxon names and branching order are identical in all panels of the figure. Only the Afrotheria + Notolegia tree (i.e., 9) is shown. The data for all tree topologies examined is available as supporting information. (A) The placental interface describes the degree of invasiveness of fetal (i.e., placental) tissue into maternal tissue, with epitheliochorial being least invasive and hemochorial being most invasive. (B) The shape of the contact zone between fetal and uterine tissues. (C) The form of interdigitation between fetal and maternal tissues. Parsimony and Markov model likelihood reconstructions were constructed by using the data file available as supporting information.