One of the hidden pitfalls of paleontology is the huge stretches of time involved, and the ease with which one can lose track of the vast enormity these simple numbers represent. For example, the five-million-year difference between an animal that lived 105 million years ago and one that lived 100 million years ago sounds too brief to take seriously, but can harbor a deceptively large amount of evolutionary activity.
Take the case of Epidexipteryx, a newly discovered feathered creature, with an elaborate tail, that lived about 100 million years ago. Paleontologists have been quick to identify Epidexipteryx as a "dino-bird," but as one blogger points out, it may in fact have been a "secondarily flightless" bird. In other words, since true birds were on the scene by the early Cretaceous period, there was sufficient time for one branch to "de-evolve" from its avian habits and, well, assume the appearance of a feathered dinosaur!
So what, exactly, was Epidexipteryx? Pending further fossil discoveries, no one can say for sure, though of course you're free to speculate.