Not necessarily. A recent study (can't track down the exact reference to
it - I only glanced across it while looking for something else - someone
help me please.... :S) looked at a close fossil relative to platyrrhines
(New World monkeys) which has been considered nocturnal because of its large
orbits. CAT scans of the braincase showed, however, that the olfactory bulbs
in this beastie were fairly small, despite a sense of smell being usually
well-developed in nocturnal mammals. The authors concluded that the animal
was more likely to have been diurnal, and the large orbits were a relic from
nocturnal ancestors (which it definitely had).
Caution - I don't think the living douroucouli (Aotus), the only
nocturnal monkey, has much of a sense of smell, but this is at least one
feature which indicates that its nocturnal habits are secondarily derived
from a diurnal ancestor.
Cheers,
Christopher Taylor
On 15/5/04 8:22 am, "david peters" <davidrpeters@earthlink.net>
<mailto:davidrpeters@earthlink.net> wrote:
Forgetting all aquatic and juvenile creatures for the moment,
if one comes across a taxon that has (relatively) much larger orbits and
sclerotic rings
than its sister taxa, can we assume that we're dealing with a nocturnal
variation?
Just wondering,
David Peters
St. Louis