"Ga-Matoran must be very friendly sorts. If I saw something that size flying toward me, claws ready to grab, I don't know that I would be welcoming it with open arms. Unfortunately, the Visorak don't care if a creature is 'friendly' or not - they want them all in their web - so I will do the best I can to snare these things for their own protection"
Their fins allow them to move in water and gave them the ability to fly. Proto Drakes captured prey by using the claws on their fins and tail. They actually got their name for their habit in bathing in Ta-Metru vats. Onu-Matoran have theorized that these Rahi do this to remove parasites that attached themselves to the Drake's body. Some Proto Drakes live around The Pit, in the area known as Razor Whale's Teeth and hunted Takea sharks.
Following the collapse of the Matoran Universe, all its inhabitants evacuated onto Spherus Magna, with the Proto Drakes likely being rescued from the robot at some point afterwards.