Figure 10. Distribution of oil droplet types within vertebrates. Taxa in black are not known to have any members with oil droplets in their photoreceptors. Those in cyan have members with photoreceptors with oil droplets which do not appear to have any color when viewed with a light microscope. Those in red have members with colored oil droplets such as those depicted for the turtle in Figure 9B. The homology of oil droplets and their pigments is presumed here, so conclusions which might be drawn from this figure (e.g., pigmentation in oil droplets arose only once and was subsequently lost in mammalian and amphibian lineages) should be accepted with caution. However, the presence of pigmented oil droplets in nearly all major reptilian taxa does suggest that such droplets are basal to at least that group. The dashed green line suggests an alternative branching for Chelonians as recently suggested by Hedges and Poling (1999). This figure is meant to show the branching pattern only; no significance should be accorded the relative lengths of the branches. (Adapted from Robinson 1994).