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. 2014 Jul 25;8:61. doi: 10.3389/fnint.2014.00061

FIGURE 1.

FIGURE 1

The phyletic relationships of select primates and the sister taxon Dermoptera (the Sunda colugo, Galeopterus variegatus). The distinction between nocturnal (black zone) and diurnal (white zone) activity patterns is strongly associated with variation in retinal ganglion cell (RGC) counts (mm-2), cone densities (mm-2), and rod densities (mm-2) in the area centralis or fovea centralis (data sources: Webb and Kaas, 1976; Perry and Cowey, 1985; Curcio et al., 1990; Wikler and Rakic, 1990; Silveira et al., 1993; Ogden, 1994; Wilder et al., 1996; Hendrickson et al., 2000; Dkhissi-Benyahya et al., 2001; Peichl et al., 2001; Ross, 2004; Tetreault et al., 2004; Finlay et al., 2008; Moritz et al., 2013). Ancestral character states based in part on these values suggest a diurnal ancestry for Tarsius and Aotus; and, by extension, stem anthropoids (e.g., Ross, 2000; Williams et al., 2010). Accordingly, the foveae of Tarsius and Aotus are most likely vestigial traits. A problem with this view is evident in the densities of RGCs, cones, and rods. Relative to Tarsius, the retina of Aotus has advanced further toward a nocturnal phenotype despite a substantially younger vintage of 5–20 million years (see text).