"Well, not any more," Levine said, "because the evolutionary arms race continued, Eventually, antelopes learned that they could only browse for a short time. Once the trees started to produce more tannin, they had to stop eating it. And the browsers developed new strategies. For example, when a giraffe eats an acacia tree, it then avoids all the trees downwind. Instead, it moves on to another tree that is some distance away. So the animals have adapted to this defense, too."
"In evolutionary theory, this is called the Red Queen phenomenon," Malcolm said. "Because in Alice in Wonderland the Red Queen tells Alice she has to run as fast as she can just to stay where she is. That's the way evolutionary spirals seem. All the organisms are evolving at a furious pace just to stay in the same balance. To stay where they are."
Arby said, "And this is common? Even with plants?"
"Oh yes," Levine said. "In their own way, plants are extremely active. Oak trees, for example, produce tannin and phenol as a defense when caterpillars attack them. A whole grove of trees is alerted as soon as one tree is infested. It's a way to protect the entire grove - a kind of cooperation among trees, you might say."
Arby nodded, and looked out from the high hide at the apatosaurs, still by the river below. "So," Arby said, "is that why the dinosaurs haven't eaten all the trees off this island? Because those big apatosaurs must eat a lot of plants. They have long necks to eat the high leaves. But the trees hardly look touched."
"Very good," Levine said, nodding, "I noticed that myself."
"Is that because of these plant defenses?"
"Well, it might be," Levine said. "But I think there is a very simple explanation for why the trees are preserved."
"What's that?"
"Just look," Levine said. "It's right before your eyes."
Arby picked up the binoculars and stared at the herds. "What's the simple explanation?"
"Among paleontologists," Levine said, "there's been an interminable debate about why sauropods have long necks. Those animals you see have necks twenty feet long. The traditional belief has been that sauropods evolved long necks to eat high foliage that could not be, reached by smaller animals."
"So?" Arby said. "What's the debate?"
"Most animals on this planet have short necks," Levine said, "because a long neck is, well, a pain in the neck. It causes all sorts of problems. Structural problems: how to arrange muscles and ligaments to support a long neck. Behavioral problems: nerve impulses must travel a long way from the brain to the body. Swallowing problems: food has to go a long way from the mouth to the stomach. Breathing problems: air has to be pulled down a long windpipe. Cardiac problems: blood has to be pumped way up to the head, or the animal faints, In evolutionary terms, all this is very difficult to do."
"But giraffes do it," Arby said.
"Yes, they do. Although giraffe necks are nowhere near this long. Giraffes have evolved large hearts, and very thick fascia around the neck. In effect, the neck of a giraffe is like a blood-pressure cuff, going all the way up."
"Do dinosaurs have the same cuff?"
"We don't know. We assume apatosaurs have huge hearts, perhaps three hundred pounds or more. But there is another possible solution to the problem of pumping blood in a long neck."
"Yes?"
"You're looking at it right now," Levine said.
Arby clapped his hands. "They don't raise their necks!"
"Correct," Levine said. "At least, not very often, or for long periods. Of course, right now the animals are drinking, so their necks are down, but my guess is that if we watch them for an extended period we'll find they don't spend much time with their necks raised high."
"And that's why they don't eat the leaves on the trees!"
"Right."
Kelly frowned. "But if their long necks aren't used for eating, then why did they evolve them in the first place?"
Levine smiled. "There must be a good reason," he said. "I believe it has to do with defense."
"Defense? Long necks?" Arby stared. "I don't get it."
"Keep looking," Levine said. "It's really rather obvious."
Arbv peered through binoculars. He said to Kelly, "I hate it when he tells us it's obvious."
"I know," she said, with a sigh.
Arby glanced over at Thorne, and caught his eye. Thorne made a V with his fingers, and then pushed one finger, tilting it over. The movement forced the second finger to shift, too. So the two fingers were connected…
If it was a clue, he didn't get it. He didn't get it. He frowned.
Thorne mouthed: "Bridge."
Arby looked, and watched the whip-like tails swing back and forth over the younger animals. "I get it!" Arby said. "They use their tails for defense. And they need long necks to counterbalance the long tails. It's like a suspension bridge!"
Levine squinted at Arby. "You did that very fast," he said.
Thorne turned away, hiding a smile.
"But I'm right…" Arby said.
"Yes," Levine said, "your view is essentially correct. Long necks exist because the long tails exist. It's a different Situation in theropods, which stand on two legs. But in quadrupeds, there needs to be a counterbalance for the long tail, or the animal would simply tip over."
Malcolm said, "Actually, there is something much more puzzling about this apatosaur herd."
Oh?" Levine said. "What's that?"