“And you think this is true of the dinosaurs because…”
“It’s rather obvious,” Levine said. “Just look at the behavior. When the two herds were alone, each clustered tightly among themselves. But when they’re together, the parasaurs spread out, abandoning their former herd arrangement, to form an outer ring around the apatosaurs. Just as you see them now. That can only mean that individual paras are going to be protected by the apatosaur herd. And vice versa. It can only be a mutual predator defense.”
As they watched, one of the parasaurs lifted its head, and stared across the river. It honked mournfully, a long musical sound. All the other parasaurs looked up and stared, too. The apatosaurs continued to drink at the river, although one or two adults raised their long necks.
In the midday heat, insects buzzed around them, Thorne said, “So where are the predators?”
“Right there,” Malcolm said, pointing toward a stand of trees on the other side of the river, not far from the water.
Thorne looked, and saw nothing.
“Don’t you see them?”
“No.”
“Keep looking. They’re small, lizard-like animals. Dark brown. Raptors,” he said.
Thorne shrugged. He still saw nothing. Standing beside him, Levine began to eat a power bar. Preoccupied with holding the binoculars, he dropped the wrapper on the floor of the hide. Bits of paper fluttered to the ground below.
“How are those things?” Arby said.
“Okay. A little sugary.”
“Got any more?” he said.
Levine rummaged in his pockets and gave him one. Arby broke it in half, and gave half to Kelly. He began to unwrap his half, carefully folding the paper, putting it neatly in his pocket.
“You realize this is all highly significant,” Malcolm said. “For the question of extinction. Already it’s obvious that the extinction of the dinosaurs is a far more complex problem than anyone has recognized.”
“It is?” Arby said.
“Well, consider,” Malcolm said. “All extinction theories are based on the fossil record. But the fossil record doesn’t show the sort of behavior we’re seeing here. It doesn’t record the complexity of groups interacting.”
“Because fossils are just bones,” Arby said.
“Right. And bones are not behavior. When you think about it, the fossil record is like a series of photographs: frozen moments from what is really a moving, ongoing reality. Looking at the fossil record is like thumbing through a family photo album. You know that the album isn’t complete. You know life happens between the pictures. But you don’t have any record of what happens in between, you only have the pictures. So you study them, and study them. And pretty soon, you begin to think of the album not as a series of moments, but as reality itself. And you begin to explain everything in terms of the album, and you forget the underlying reality.
“And the tendency,” Malcolm said, “has been to think in terms of physical events. To assume that some external physical event caused the extinctions. A meteor hits the earth, and changes the weather. Or volcanoes erupt, and change the weather. Or a meteor causes the volcanoes to erupt and change the weather. Or vegetation changes, and species starve and become extinct. Or a new disease arises, and species become extinct. Or a new plant arises, and poisons all the dinosaurs. In every case, what is imagined is some external event. But what nobody imagines is that the animals themselves might have changed-not in their bones, but their behavior. Yet when you look at animals like these, and see how intricately their behavior is interrelated, you realize that a change in group behavior could easily lead to extinction.”
“But why would group behavior change?” Thorne said. “If there wasn’t some external catastrophe to force it, why should the behaviour change?”
“Actually,” Malcolm said, “behavior is always changing, all the time. Our planet is a dynamic, active environment. Weather is changing. The land is changing. Continents drift. Oceans rise and fall. Mountains thrust up and erode away. All the organisms on the planet are constantly adapting to those changes. The best organisms are the ones that can adapt most rapidly. That’s why it’s hard to see how a catastrophe that produces a large change could cause extinction, since so much change is occurring all the time, anyway.”