Though commonly mistaken for Archeopteryx, the difference between the two theropods is the microraptors blinding speed, and ability to leap up into the air and orbit the player until stunning them and dismounting them from any creature they're on. Keep an eye on the bushes and trees, they can be anywhere in the redwoods forest.
They seem to only be aggressive when you are on your mount. Dismount before approaching or else you will find your self thrown off and Stunned. Walking forward and backwards quickly allows you to "hula hoop" an attacking Micro, giving you time to dismount and avoid the stun.
My tribe mate got stunned by one these while he was peacefully getting ripped to shreds by 1 thyacoleo, a swarm of bugs and a pack of terror birds. Guess which one caused his death? The microraptor because it stung him and he couldn't fight back.
If you hear one scrwam or you just hear battle music flare up out of nowhere, dismount IMMEDIATELY. They can only stun you while you're on your mount so if you get off before it reaches you it won't stun you when they hit. Its much better to be off your mount for a bit during a battle rather than being stunned AND dismounted in the middle of a battle.