“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 to leap.”

He was paying no attention at all to his auditor now, caught up once again in the drama of the fossil. Life pursued by death. It was an experience common to all creatures, but somehow it always came as a surprise when it actually happened.

“Could the apatosaur outrun them? It’s possible. If it could get up to speed quickly enough. But something that big simply can’t accelerate as fast as the allosaurs can. So it has to turn—here, where the three tracks converge—and fight.”

He double-clicked the trackball’s right button to zoom up so that they could see a larger area in the screen.

“This is where things get interesting. Look how confused the trackway is—all these trampled places, all this churned-up mud. That’s what makes this fossil unique. It’s the actual record of the fight itself. Look at those footprints—hundreds of them!—where the apatosaur is struggling with its attackers. See how deep these paired footprints are? I haven’t worked out the ergonomics yet, but it’s possible the brute actually rears up on its hind legs and then falls forward again, trying to crush its tormentors. If it can only take advantage of its immense weight, it can still win the battle.