You are in the floodplains of North America, 150 million years ago.

The air was thick and humid, smelling of damp earth and cycads. You were tracking a small herd of Stegosaurus when the ground began to tremble—not a sharp, sudden quake, but a rhythmic, deep thud that vibrated through the soles of your boots.

Emerging from the mist near the riverbank, a herd of Brontosaurus appeared, more like walking mountains than animals. Three massive adults led the way, their necks—long as ship masts—swaying slowly as they stripped leaves from the tops of trees that no other herbivore could reach. Their skin was rough and grey-brownish to green, blending with the jungle, but the sheer scale of them was impossible to hide.

One of them paused, its remarkably small head turned slowly toward your hiding spot. You held your breath, frozen. The eye was dark and indifferent, seemingly aware of you but finding you utterly harmless. As it continued grazing, its immense tail, nearly 50 feet long, lashed lazily, shattering a small, petrified tree stump.