The Moai Statue is an archaic naturally spawning structure that can be found uncommonly on beaches. It was added in Build 7.3, the 'Dinosaur Renaissance' update. They are very large, at 15 blocks tall and 5 blocks long, but can sometimes spawn with up to half their body buried in sand. They also sometimes spawn with a clay hat.
It is based off the real-life Polynesian statues on Easter Island carved between 1250 and 1500 CE, and still exist today.