From Bulbanews, your community Pokémon newspaper.
'''Sugimori:''' I worried about it for a while, and I eventually went to go see the sea otters at the aquarium. I happened to catch the sea lion show while I was there, and I became aware of the sea lion's power. "Well, let's try blending a sea otter and a sea lion," I thought. I came up with the idea of making the shell on Mijumaru's stomach into a sword (katana) and using it to fight, and that's how I completed Mijumaru and its evolution."|Pokémon Pia|cat=notatall}}
The information provided seems to indicate that the starters' evolutions leaked previously were fake.