Osteological evidence for the evolution of activity pattern and visual acuity in primates

Area of Science:

• Primate paleontology
• Comparative anatomy
• Evolution of vision

Background:

• Orbit size correlates with activity patterns in primates, with nocturnal species having larger orbits.
• Optic foramen size relates to retinal summation and visual acuity, with diurnal haplorhines showing larger foramina and higher acuity.

Purpose of the Study:

• To investigate the relationship between orbit size, optic foramen size, and visual adaptations in living primates.
• To infer the activity patterns, retinal anatomy, and visual acuity of fossil primates using osteological variables.

Main Methods:

• Comparative analysis of orbit and optic foramen sizes in extant primate species.
• Measurement and comparison of these osteological variables in fossil primate taxa.

Main Results:

• Nocturnal primates have larger orbits than diurnal species; nocturnal haplorhines exhibit extreme orbital hypertrophy.
• Diurnal haplorhines possess larger optic foramina, less retinal summation, and higher visual acuity.
• Fossil primates like omomyiforms and adapiforms were classified as likely nocturnal or diurnal based on orbit size.

Conclusions:

• Orbit and optic foramen sizes are reliable indicators of activity patterns and visual capabilities in fossil primates.
• Specific fossil taxa were inferred to have nocturnal (e.g., Plesiopithecus, Microchoerus) or diurnal (e.g., Leptadapis, Adapis) adaptations.
• Fossil primates generally lacked the extremely high visual acuity characteristic of extant diurnal haplorhines.