Kalman Rubinson <kr4 at is2.nyu.edu> wrote:
:> The mammal with the largest neocortex when the effect of
:> body mass scaling is removed (that is, neocortical volume
:> devided by bodymass^0.65) is the Echidna.
: This is misleading. A better index of cortical 'size' is the surface area
: of the thin mantle of cortex. Echidna cortex is lissencephalic (smooth
: and not significantly formed into gyri and sulci) and, therefore, it is
: unlikely that the echidna has high ratio of 'cortex' to body mass.
You are confusing monotrmes with marsupials.
The Echidnan neocortex _is_ folded into sulci ang gyri. And the
ratio of neocotical wolume to residual brain wolume is larger than
for any other known mammal, humans included.
The evolutionary transition from monotrmes to marsupial are, among
onther things, charcterised by a massive reduction in neocotrical
surface area and the ratio of neocortical volume to residual
brian volume. Another features that evolved during this transition
are REM sleep and live birth.
Sturla Molden