You find yourself enveloped in a dense, humid mist. Every breath of air you take is so thick that you can practically drink it, and it's heavy with the damp, sulfurous stench of stagnation and decay. Across the rough trail ahead of you, a fallen tree trunk suddenly begins to move in a very unsettling way,

writhing and scuttling across the ground. It's not a down tree at all, but a giant millipede,

the biggest land invertebrate of all time, a prehistoric creature called arthroplura.

It's an easy mistake to make because arthropura is around two and a half

meters long and nearly 60 centimeters wide. And it isn't alone because you've barely had time to

process the size of this enormous bug before another flies right past you, Megynura, a dragonfly

relative about the size of a pigeon, you're standing in the

middle of a late Carboniferous swamp, hugging the shore of a shallow sea around 310 million years ago.

The ground is muddy and wet, and you need to watch your step. Since the rise of the first forest

in the Devonian period, plants have

continued to diversify and cover the continents, raising the oxygen level in the atmosphere

to new heights. With little competition from other animals on land, insects and other

arthropods are living large. And they're not the only things that are. Giant tree-like plants dominate this landscape,

reaching upwards of 50 meters tall. They're mostly lipididendron, sometimes called scale trees,

though they're not quite like any trees you've ever seen before. Their green trunks are made

of living photosynthetic tissue and textured like alligator skin with a pattern of diamond-shaped scales.

These long, scaly green poles branch only at their very top, where they fork to form crowns of narrow spiraling leaves shaped like huge blades of grass.

And surrounding these giants are many other plant species that form a thick and complex

swamp understory.

It's tough to find a path and you try not to trip over exposed roots.

The endless green is broken up only by blue-gray pools of murky swamp water, and the brown fallen trunks,

branches, and foliage of dead plants. And as this plant debris gradually sinks into the watery

...