You are in the outback deserts of Australia, 50,000 years ago.

The sun was barely skimming the edge of the Pleistocene acacia scrub when you smelled them—a musky, heavy scent, like damp fur and crushed eucalyptus. You froze behind a thicket.

They weren't moving like the kangaroos you knew; there was no bounding, just a deliberate, rhythmic, bipedal swagger, almost human-like.

A small herd of Procoptodon was feeding near the dry riverbed. There were five of them, towering nearly seven feet tall, their short, flat, "running-into-a-wall" faces scanning the horizon. The largest one proped itself up on its enormous, single-toed hind foot and stiff tail, stretching upward to browse on the high branches that were far out of reach for any modern creature. They didn't look like monsters, but they felt like gods of the scrub. The sun caught the dusty, dense fur on their shoulders, and you could see the single, long claw on each of their hands as they pulled leafy branches toward their mouths.

One of the Procoptodons stopped chewing, its eyes, uniquely forward-facing, locked in your direction…