Well, I think only two species are possible since you saw this squirrel near the Osa Peninsula. I'm quite sure it's Microsciurus alfari based on the coloration, a not that bushy tail and the ears. I don't think it's a Red-tailed Squirrel. The local subspecies of the Variegated Squirrel, S. v.melania, is a melanistic form. Deppe's and Montane Squirrel doesn't inhabit the southern Pacific region.
