Welcome to KaW forums! I see this is your first post, and you are asking a good question. Unfortunately, none of the players can answer your question specifically. You'd probably get a better answer by sending an email to support@athinkingape.com. But generally, the answer to your question is someone hired by A Thinking Ape, the creators of this game.
I am pretty sure that the sea monster for TFO and what not was a community entry. Other than that most probably came from the developers.