Click here for Wild Mass Guessing for the series as a whole.
Petey Piranha was created by the Shroobs.
He's the only Piranha Plant to have Petals on his head, he still has green lips despite Piranha Plants being redesigned to have white lips, and he has arms. Petey was once just a normal Piranha Plant, but was mutated via experiments from the Shroobs. And these experiments gave him a very long lifespan, which is why he hasn't aged between the time the Mario Bros. were babies and the present day. The reason Dino Piranha and Peewee Piranha from the Super Mario Galaxy duology look similar to him is because a few remaining Shroobs would later use DNA samples from Petey on alien dinosaur eggs.
