Bones of the Earth

He held one hand on the trackball, so he could scroll through the program as he talked. "One hundred forty million years ago, an Apatosaurus -- what used to known as Brontosaurus, before the taxon was reattributed -- is out for a stroll along the shores of a shallow lake. See how steady the apatosaur's prints are, how placidly it ambles along. It is not yet aware that it's being hunted."

Griffin gravely folded his hands as Leyster scrolled down the trackway. They were enormous hands, even for a man of his bulk, and strangely expressive.

"Now look at these smaller sets of prints here and here, coming out of the forest and following along to either side of the apatosaur's prints. These belong to a hunting pair of Allosaurus fragilis. Killer dinosaurs twelve meters long, with enormous sharp claws on their hands and feet, and teeth as large as daggers but with a serrated edge. They move more swiftly than their prey, but they're not running yet -- they're stalking. Notice how they've already positioned themselves so they can come up on it from either side.

"Here, the apatosaur becomes aware of its danger. Perhaps the wind shifts and it smells the allosaurs. Maybe the creatures scream as they attack. We'll never know. Whatever alerted it left no trace in the fossil record.

"It runs.

"See how the distance between strides increases. And see how back here, the same thing happens to the allosaur tracks. They've gone into an all-out sprint. They're charging, much like a lion charges its prey. Only, their prey is as big as a mountain and they themselves are so large and fierce they could eat lions for breakfast.

"Now look, see how there's a little skip here in the one allosaur's tracks, and an identical one here in the other's. They're matching strides with the apatosaur. For the rest of the chase, they're all three running in lockstep. The allosaurs are in position..."