| الملخص: |
An anterior position of the foramen magnum is often cited as a correlate of bipedal posture in hominids. Other investigators (Biegert 1963) have suggested that it more accurately reflects increased encephalization. The present study examines this problem in bats, which most commonly employ an inverted but orthograde posture during rest but all which participate in active flight. The position of the foramen magnum was evaluated using Bolk’s Basal Index (1909). A mean Basal Index was obtained for ten species of bat belonging to the pteropodidae subfamily, and twenty belonging to the Phyllostomidae subfamily. Measures of brain volume and were obtained from Baron (1996) and used to create two different indices of neural organization: An Encephalization Quotient (Brian volume/Body volume) and Neocortical Quotient (Neocortex volume/Telencephalon volume). A strong negative correlation was found between Neocortical Quotient and Basal Index in both Pteropodidae (r= -.717) and Phyllostomidae (r= -.566), as predicted by Biegert’s hypothesis. A linear model shows an interaction between subfamily and Neocortical quotient (r2 = .828). Since substantial variation in locomotor pattern and/or posture does not obtain within this group of bats, this confounding variable can be excluded. These data provide strong evidence that the position of the foramen magnum may be used as a potential indicator of neural reorganization (in particular, expansion of the neocortex), but not as an indicator of posture. |
