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In the latter cause, Horner heads out each day with his fossil hunter's pick in one hand and a cigarette in the other. The hillsides are pocked with deep sinkholes and covered with bentonite, a loose mudstone that gives the sensation of walking on popcorn. When Horner slips, he drives the pick in up to its haft and hangs on as it plows a neat furrow 30 feet down a hillside without catching on anything solid. If this were an Indiana Jones movie, he would smash into something wonderful at the bottom -- the skull of a Pachycephalosaurus, say. In real life, all Horner gets is a banged-up human knee.
Triceratopses can be had cheap hereabouts. Horner picks his way through the litter ("Rib city," he remarks, dismissively) with an eye for the shape of the land as it was in the Cretaceous, when rivers from the Rockies flowed through eastern Montana into a vast central seaway. At one point he kneels and works at some potentially good thing with a car mechanic's gasket scraper, then sweeps off the debris with a whisk broom. A visitor asks what he has found. "I haven't got a clue," he says, wrapping the pieces of bone in toilet paper. "That's why I'm taking it." Elsewhere he stops at an unusual fossil spotted the night before by a graduate student out fishing, who excavated it part way with a daredevil spoon intended for catching bass, not dinosaurs. "It's a metatarsal," Horner says, completing the job. "Ornithomimid. And a darn nice one at that."
One day in 1977, while fossil hunting with his father in Montana's Two Medicine formation, Horner picked up a rock that resembled a squashed turtle. It turned out to be one of the first intact dinosaur eggs ever found in the western hemisphere, and Horner's work at Princeton thus came to focus on one of paleontology's great mysteries: the almost complete absence of juvenile dinosaurs, especially babies, from the fossil record. He went back to Montana the following summer, with the idea of spending his vacation searching for babies in some likely shales, in the company of a beer-drinking, fossil- hunting pal named Bob Makela. They wound up one Sunday morning helping the owner of a rock shop in Bynum identify some of her fossils. Among them was a coffee can full of bones from a recent dig, including a fragment of a thumb- size femur. "You're not going to believe this," Horner remarked to Makela when he picked it up.
The femur and a collection of other bones back at the house were from baby duckbills. The shop owner took the two paleontologists to a ranch near Choteau where she had found the fragments, and during the next few weeks the scientists unearthed an entire nest 6 ft. in diameter, separating out the fossils with a garden hose and a window screen. To nonpaleontologists, Horner writes in his recent book, Digging Dinosaurs (Workman Publishing; $17.95), the fossils resembled "a bunch of black, sticklike rocks -- jumbled and inscrutable, the way much of modern art seems to me." But to Horner, they were the remains of 15 duckbill babies, almost ready to leave the nest. Nearby he also found the adults that had apparently reared their offspring to this stage. From such evidence as the worn teeth and incompletely formed bones of the nestlings, Horner inferred that the parents were sharing food with them and, from their growth rate, that they were warm blooded.