36

She's right. Could a T. rex hide behind one of those massive sequoias? You have no idea. Everything is so quiet. Have all its prey fled? You shiver despite the heat. But wait. "Lots of dinosaurs have three toes."

"This big?" Brett shakes her head.

"Yes, this big. Think of all the fossils we've seen in museums back home." You scrutinize the print more closely. Relief floods through you. "T. rex has claws at the tips of slender toes. Look here—fat toes—no claw marks."

Brett's not terribly convinced, so you pull out a laminated chart of dinosaur footprints, which are slightly different than the drawings downloaded in your cell phone app. You point to the T. rex example. It's decidedly unlike whatever stomped through this mud. Nonetheless, you wonder how exactly you can tell if it prowled these woods ten minutes ago or ten hours or ten days.

Your friend waves a dismissive hand at your chart. "Nobody's one hundred percent certain that's what a Tyrannosaurus footprint looks like."

"Fair point. But we know a T. rex print has to have claws, and this dinosaur doesn't."

"So what do you want to do?"