Counterpoint: tiny terrestrial mammals becoming whales.
Whales came onto land, said fuck this and walked right back into the sea. It is widely regarded as a good decision in whale culture.
More importantly, actual evolution doesn’t change the individual. The “evolution” in Pokémon and Digimon should be called “development”.
Yo, I have chickens. The idea of a chicken the size of a pony is terrifying enough. One the size of a t-rex is nightmare inducing.
I love ours, they’re pets that get spolied and coddled. But they are vicious. Our rooster caught a little bluebird, stomped it and ate its head. Took all of thiry seconds. Our hen goes after bugs and just beats them until they’re tender and juicy before swallowing.
They would 100% eat us given a chance. Like, at the size they are now, you would not want to fall into a coma long enough for them to get hungry.