This thing should be the island itself, or rather, the cornerstone of the island. It originally lay dormant underground, with the jungle and hills as its hair. Now 'Shield' has cleverly shaved it bald, naturally it would 'leap up' and hold the barber accountable.
Professor Liu once said that many of the plants and animals on the island are prehistoric species, possibly even from the same era as dinosaurs. They have formed an independent evolutionary circle in this closed environment.
The island is so ancient, so the giant beast serving as the island's foundation should also be a prehistoric creature. Without it, the island would undoubtedly sink into the sea. Such a massive creature couldn't have burrowed under the island later.
As big as the island is, so is it, including the area beneath our feet that was originally sea bottom, which is also part of its body.
