As leaves go, this one certainly does not look like a keeper. The alder leaf is full of holes caused by a marauding insect and is not the sort you would collect and press between the pages of a book, even if it weren't stone — a 48-million-year-old fossil. But it is precisely the ugly, insect-munched holes in the object at hand that fascinate Conrad Labandeira, of the Smithsonian's National Museum of Natural History.
Labandeira is curator of fossil arthropods, which include fossil insects, and he studies insect variety, distribution and activity going back millions of years in the fossil record. Labandeira's brand of science often requires him to collect not only the good specimens, but the bad and, in the case of insect damage, the ugly. In fact, sometimes they're the best.
One of the key places to go to collect insect-nibbled samples of the fossil record is the small town of Republic, east of the Cascade Mountains in Washington State. "All major types of herbivory appear to be present at Republic," says Labandeira, speaking broadly of plant eating. "The fossils go about as far back as we can go in the fossil record and still record insect damage on the standard, or closely related, genera of plants that occur today."
Republic dates back to the Eocene, the epoch when the earliest relatives of many of today's familiar plants took root. What's more, Republic was a crossroads between highlands and lowlands, warm climate and cool, north and south. Plants thrived together there that have not been found together anywhere else. It was also where many modern plant lineages that attract predatory insects made their earliest appearances, placing the Republic flora among the oldest in which modern plant-insect associations can be traced in the fossil record.
That is why, one recent fall, Labandeira and Kirk Johnson, curator of paleontology at the Denver Museum of Natural History, headed out to Republic, joined by Wesley Wehr, affiliate curator of paleobotany at the Burke Museum of Natural History and Culture in Seattle. Together they collected samples from the more than 300 types of leaves, cones, fruits, seeds, flowers and insects to be found there.
Tlick-tlick-tlick, tlick-tlick-tlick. Beneath a candy-striped canopy, more than a dozen people with hammers and chisels work Boot Hill, an unassuming pile of rock and dirt that lies at the north end of Republic. They are "Leaf Whackers," volunteers from Johnson's museum. With others from the Burke, they split open slabs of outcrop as quickly as a shale-prying colleague can deliver them, the layers dried and loosened with a weed burner that looks like a flamethrower. This is the first large-scale, systematic dig at Republic.
Johnson's eyes are locked on a just-delivered rock. "Look at the beautiful angiosperms. That's the fun stuff, this forest coming up out of the ground, hearing the oohs and aahs." He passes the fossil to two Leaf Whackers at a nearby picnic table, who catalogue it on the spot for the Denver Museum's collection. Johnson describes this as the "blitzkrieg method — we bore into the hill, and we get years of data in one week. Bit by bit the various fossils check in. To get this many samples would take one person two years." By the time the five-day dig is up, they will have chipped out and logged more than 1,500 fossils, far more than the minimum number of samples required for an unbiased reconstruction of the Republic flora, the plants represented pretty much in the proportions in which they lived.
Over the past two decades, Wehr has brought legions of other paleontologists to Republic — and taken pieces of Republic to them. Among the more than 3,000 Republic specimens Wehr and his assistants have gathered for museum collections are the first known occurrences of fir, apple, blackberry, holly, horse chestnut and other plants with living relatives.
None of this interest in Republic would have been piqued had not Wehr and Johnson come over the mountains from Seattle in 1977, when Johnson was only 17, to see what they could find. The route they followed from Seattle is an imitation of how geological events literally made Republic what it was. Like many visitors, they came to the town by way of the North Cascades Highway. East of the mountains, the first town Johnson and Wehr hit was Winthrop. One hundred million years ago, Winthrop would have been on the east coast of a big island, the North Cascades subcontinent, which was banging into North America. The land Wehr and Johnson were headed for, the Okanogan subcontinent, where Republic roosts today, had already merged into North America.
As the North Cascades and Okanogan subcontinents collided, what was left of the ocean floor between them was pinched against and beneath the Okanogan. The pressure caused the Okanogan to bulge, raising the elevation perhaps as high as 4,500 feet above sea level.