Very dangerous, very annoying. Also kinda cute. This is the compy, or compsognathus. It is a pack dino, which means it gets a pack bonus if there are other compies around. They are very small, which means if you attack one, others could quickly stream out of the small berry plants. However, they are relatively slow and quite low on health, so if many threaten you, don't bother fighting them. 1. Because it's a bad idea for new/low lvl players. 2. Because they barely give any hide or meat
A single Compy is never an issue. Due to there curious nature of humans they'll walk right up to you and observe you without hostility. But after they see you they will send out a call to nearby Campus beckoning them. Once another Compy is close enough to get a pack bonus they loose there neutral mentality and the pack mind takes over and they become hostile to beware of multiple Compys.
Although their small stats may make you heavily underestimate them, don't be fooled. These little guys rely on confusing you, and are very small and hard to hit. In high leveled groups with lots of members, they can be extremely deadly early game. For dealing with the annoying groups, just use a torch. If you cannot beat them, and they are overpowering you, I can help. A strategy I've found works is probing (default key X) under a large creature with a neutral temperature, preferably a herbivore with a large hitbox on its body and attacks (a Triceratops would be perfect). This may result in you being hit, but the Trike will kill off all the Compies, giving you time to run, or collect their spoils.