Probably one of the best general use non flyer mounts in the game. Fast land and water speed, quick stamina regen, good health, decent damage. Small enough to use in some caves like the southern cave. Absolute terror in the water and it has no oxygen meter. Very easy to tame and can be found in the swamp or around some rivers. High maneuverability on land and in water.
Baryonyx are quick like Allosaurus and do just as much damage (but don't get a pack bonus). They don't use oxygen for swimming and can sprint in the water. Right click in the water does an AoE stun that lasts about 10 sec. Their 'C' is a... Taunt? They also jump and you can fire a weapon from their back.
It's like a small Allo combined with a Kapro, in my opinion. Useful on both land & in the water. Use its secondary attack while swimming to stun, attack, and harvest. Does NOT stun Cnidarias, though, so do not expect to overpower them.