It’s not a dinosaur, whale, or giant deep-sea creature its a fungus. Its an underground fungus that most people wouldn’t notice even if it was right beneath their feet. The fungus, Armillaria ostoyae, covers more than 3.4 square miles its around 8.8 square kilometers. It resides in Oregon’s Malheur National Forest and is more than 2,400 years old. It exists as a network of inter joined underground fungus filaments. Every fall its flowers/mushrooms/whatever they’re called rise above the surface in the form of edible honey mushrooms. The most impressive part is the slow growth of just 1 meter per year.
https://owlcation.com/stem/largest-living-thing-on-earth