Troodons are the most dangerous creatures in Ark for humans. At daytime, they can be seen alone, wile at night they stand together and their eyes glow. They can knock a human out in no time, making them even more dangerous. They drain your tames stamina really quick. However, they can be easily killed by ranged weapons.
At lvl 72 with flak armor on, a lvl 5 Troodon knocked me out with one attack at night. Last thing I saw was those glowing eyes before passing out. My Guess is that they attack vital organs. Luckily my Doedicarus was up for a game of baseball and launched that little devil out into the stands.