Red-crested tree rat
This adorable rodent — only known because of the existence of two specimens captured in Colombia in 1898 — hadn't been seen for over a century and was feared extinct. That is until one simply ambled up to a pair of biologists in May 2011 while they were camping in the field. The creature even stuck around for a photo shoot before wandering back into the dark forest.
Distinctive for a fiery-red patch of fur on its head, the red-crested tree rat is as cute as it gets. One can only hope that it will not disappear again for another 100 years.
It's impossible to say from this single finding how many individuals exist, but given that extensive searches for the animal have turned up nothing until now, it's safe to say that it's extremely rare. Where there's one, there are probably others.