From the official release announcement - Become the apex predator with Prehistoric Skins:
"Nothing can stop them. Well, besides asteroids… and tar pits… and the ice age.
Teach your enemies a lesson on extinction with Prehistoric Cho’Gath, Prehistoric Anivia, and Prehistoric Renekton, now available in the depths of the primordial jungle and the League store for 750 RP (or you can try cloning real dinosaurs with amber-fossilized mosquitoes. Although we don’t recommend it)."Click on each of the skins loading screen slice to jump to preview screenshots and videos:
Prehistoric Anivia and Cho'Gath share this orientation of the shared Prehistoric splash art.
To fit snug on his champion page, Prehistoric Renekton uses a flipped version of the shared splash.