Fossil Hunters

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Nasion-inion chord (mm)

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Nasion-inion chord (mm)

Figure 8. Orbital frontation versus skull size in felids (A) and herpestids (B) (adult species means—Noble et al., 2000; Ravosa et al., 2000a). In the former, clade frontation decreases significantly with size, while in the latter, no such pattern exists (Table 3). More frontated sister taxa in both families tend to exhibit bony postorbital bars. In felids and basal primates, this is restricted to small sizes due to allometric decreases in relative brain size and thus increased orbital frontation. (Key: same as Fig. 7.)

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Plesiadapiformes

Adapidae

Omomyidae

Tupaiidae

Pteropodidae

Herpestidae

Felidae

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Figure 9. Brain mass(0 33) versus face size in plesiadapiforms, omomyids, adapids, tupaiids, felids, herpestids, and pteropodids (based on adult species means in Stephan and Pirlot, 1970; Stephan et al., 1981; Gittleman, 1986, 1991; Martin, 1990; Ravosa et al., 2000a). Versus the other clades, felids, and omomyids are significantly more encephalized for a given face size, thus suggesting the presence of increased basicra-nial flexion and greater frontation of the orbital apertures (Ravosa, 1991b,c, unpublished; Ross and Ravosa, 1993; Lieberman et al., 2000; Ravosa et al., 2000a,c).

Plesiadapiformes

Adapidae

Omomyidae

Tupaiidae

Pteropodidae

Herpestidae

Felidae

In Palate length (mm)

Figure 9. Brain mass(0 33) versus face size in plesiadapiforms, omomyids, adapids, tupaiids, felids, herpestids, and pteropodids (based on adult species means in Stephan and Pirlot, 1970; Stephan et al., 1981; Gittleman, 1986, 1991; Martin, 1990; Ravosa et al., 2000a). Versus the other clades, felids, and omomyids are significantly more encephalized for a given face size, thus suggesting the presence of increased basicra-nial flexion and greater frontation of the orbital apertures (Ravosa, 1991b,c, unpublished; Ross and Ravosa, 1993; Lieberman et al., 2000; Ravosa et al., 2000a,c).

convergence levels than diurnal sister taxa (Figures 10 and 11; also in a later section). Interestingly, the nocturnal, more frugivorous kinkajou (Potos) has a degree of orbital convergence similar to other nocturnal procyonids (Figure 11). In similar-sized didelphimorphs, four nocturnal faunivores of the genera Philander, Chironectes, and Metachirus—all possess more convergent orbits (mean = 53.5°; range= 50.4-57.8°) than three nocturnal arboreal frugivores of the genus Caluromys (mean=42.4°; range = 42.0-43.0°) (Mann-Whitney U test among species means of 30-38 mm for the nasion-inion chord, p = 0.034). Therefore, as compared to nocturnal frugivores and diurnal faunivores, only nocturnal predators appear to display marked stereoscopic visual acuity and depth perception (cf., Allman, 1977, 1982; Cartmill, 1972, 1974, 1992).

Analyses of ontogenetic series for 12 primate species (six strepsirrhines, six haplorhines) provide additional evidence regarding covariation in orbital orientation (Ravosa, unpublished). On the one hand, all 12 taxa are characterized by size-related decreases in orbital frontation during growth, such that infants are more frontated than adults (Table 4). Furthermore, strepsirrhines uniformly exhibit ontogenetic increases in orbital convergence, but their

□ Omomyidae O Adapidae

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V Lorisidae <^>Galagidae • Tarsiidae ^ Plesiadapiformes Q Tupaiidae ■ Dermoptera A Pteropodidae + Felidae T Herpestidae

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Figure 10. Orbital convergence versus face size in Eocene primates, primate sister taxa, extant primate nocturnal predators and other putative analogs (adult species means - adapted from Ravosa and Savakova, 2004). The first primates (omomyids, adapids) are similar to primate nocturnal predators (cheirogaleids, lorisids, galagids, tarsiids) and felids in exhibiting relatively higher convergence levels. The remaining mammals display more divergent orbits—tupaiids, plesiadapiforms, dermopterans, pteropodids, and herpestids. In contrast to its largely diurnal sister taxa, the herpestid nocturnal faunivore Dologale (arrow) displays a relatively greater degree of orbital convergence. These and other comparisons suggest that the derived presence of forward-facing orbits in basal primates was an adaptation for nocturnal visual predation (cf., Figure 11). Elevated convergence in diurnal adapids (cf., Cartmill, 1974; Martin, 1990) is due to the retention of basal primate (=omomyids-like) levels of convergence coupled with subsequent evolutionary increases in body size.

infants exhibit less convergence than adults (Ravosa and Savakova, 2004). On the other hand, anthropoids are characterized by postnatal increases, decreases, and isometry of orbital convergence (Table 4). Not surprising, strepsirrhines exhibit a common growth pattern, whereby orbital convergence and frontation are negatively correlated, while anthropoids show isometric or positive ontogenetic relations between convergence and frontation. Therefore, it is unlikely that a single explanation can explain both positive and negative correlations between convergence and frontation during ontogeny (Table 4) or across a clade (Table 3).

Another way the two suborders differ is in the relative level of orbital convergence and orbital frontation during postnatal ontogeny (Table 4). Anthropoid infants typically exhibit higher convergence levels than strepsirrhines

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Nasion-inion chord (mm)