The implication (at least according to the source novel) is that the park has been breeding live dinosaurs for approximately 5 years by the time the events of Jurassic Park take place.
A single large dino takes approximately 2-4 years to grow and mature.
“And how long to grow?”
“Dinosaurs mature rapidly, attaining full size in two to four years. So we now have a number of adult specimens in the park.”
They discuss the length of time it would take a hadrosaur to become full-sized.
Morris laughed, too. “A baby hadrosaur. That'd be something to see. How big were they?”
“About so,” Grant said, holding his hands six inches apart. “Squirrelsize.”
“And how long before they become full-grown?”
“Three years,” Grant said. “Give or take.”
Five years ago Hammond hired a bunch of dinosaur consultants to advise on the habitat, food and breeding of juvenile dinosaurs, suggesting that their breakthrough came at that time.
“Thirty thousand dollars a year,” Grant said, nodding. “For the last
“Because,” Morris said, “over the last five years, Hammond has
purchased enormous quantities of amber in America, Europe, and Asia,
including many pieces of museum-quality jewelry. The foundation has
spent seventeen million dollars on amber. They now possess the largest
privately held stock of this material in the world.”
“So Gennaro telephoned you in 1984. What happened then?”
“Well,” Grant said. “You see our operation here. Fifty thousand would support two full summers of digging. I told him I'd do what I could.”
“So you agreed to prepare a paper for him.”
“On the dietary habits of juvenile dinosaurs?”
“You met Gennaro?”
“No. Just on the phone.”
“Did Gennaro say why he wanted this information?”
“Yes,” Grant said. “He was planning a museum for children, and he wanted to feature baby dinosaurs. He said he was hiring a number of academic consultants, and named them. There were paleontologists like me, and a mathematician from Texas named Ian Malcolm, and a couple of ecologists. A systems analyst. Good group.”
Morris nodded, making notes. “So you accepted the consultancy?”
“Yes. I agreed to send him a summary of our work: what we knew about the habits of the duckbilled hadrosaurs we'd found.”
“What kind of information did you send?” Morris asked.
“Everything: nesting behavior, territorial ranges, feeding behavior, social behavior. Everything.”
“And how did Gennaro respond?”
“He kept calling and calling. Sometimes in the middle of the night. Would the dinosaurs eat this? Would they eat that? Should the exhibit include this? I could never understand why he was so worked up. I mean, I think dinosaurs are important, too, but not that important. They've been dead sixty-five million years. You'd think his calls could wait until morning.”