What type of creatures do they meet?
The protagonists see plenty of plant life. Things like grasses and trees are in abundance. The men also see things like giant mushrooms. Verne tells the reader that each of the organisms found resembled prehistoric plant types. As for creatures from the animal kingdom, the men see a variety of giant insects and dinosaurs. Many of the dinosaurs they saw were of the swimming variety and flying variety.
The other was the mighty Plesiosaurus, a serpent with a cylindrical trunk, with a short stumpy tail, with fins like a bank of oars in a Roman galley.
There was the giant Mastodon, twisting and turning his horrid trunk, with which he crushed the rocks of the shore to powder, while the Megatherium—his back raised like a cat in a passion, his enormous claws stretched out, dug into the earth for food, at the same time that he awoke the sonorous echoes of the whole place with his terrible roar.