Figure 8.

Comparison of the modeled relative rates of brain development for a metatherian (marsupial) and a eutherian (placental) mammal of similar adult brain sizes. The marsupial species is the Polyprodonta dunnart, the marsupial mouse, and the placental mammal is a rodent, the common mouse M. musculus. The x-axis is the event scale, and the y-axis shows the predicted PC day of the occurrence of each event in both species. In this graph, the y-axis is a linear, not a log scale, so that the differences in duration can be better appreciated in this case where brain sizes are comparable. The elevated points near the dunnart line represent the effect of the non-glires interaction term delaying cortical neurogenesis with respect to the mouse. The dunnart takes nearly twice as long to reach 80% of its adult brain size compared with the laboratory mouse, with later developmental events disproportionately protracted compared with early events.