Lileep
The Sea Lily Pokémon
Type: Rock/Grass
Official Registration #: 345
Entry: This ancient pokémon thrived at the bottom of prehistoric oceans by anchoring itself to a rock and ensnaring prey with its flower-like tentacles. It became extinct over 100 million years ago, largely due to the fact that being a stationary marine pokémon in a region where one active legendary can evaporate the ocean by taking a leisurely stroll through the general vicinity was perhaps a bad evolutionary idea.

Cradily
The Barnacle Pokémon
Type: Rock/Grass
Official Registration #: 346
Entry: The evolved form of lileep, by battle experience. As a step up from its preevolved form, cradily developed both the ability to walk and the ability to do so on land. Although one would think this would enable it to survive past the Cretaceous Era, cradily’s extinction was largely due to two major issues. First, its body, which was heavy enough to anchor it to the ocean floor, was not very well-equipped for chasing down prey. Second and more importantly, it has been scientifically proven that it’s rather difficult to survive when your children die in a mass extinction.