There used to be a persistent legend about elephants. The story went that when an elephant got old, one day it would leave the herd and make its way by instinct to the elephant graveyard—a hidden place, carpeted with the tusks and bones of generations of elephants—and lie down there and breathe its last. All the famous African expeditions of the 1800s had it on their To-Do lists: "find elephant graveyard." None ever found one.
Universal Graveyards: Lagerstätten
Paleontologists dream of finding something like the elephant graveyard—a place where fossils of everything that lived there are perfectly preserved in complete detail, even fragile things like insects, even microscopic life. It would be like a clear window into the world of the deep past, without the frustrations of dealing with isolated fragments, the way most fossil sites are. Luckily a few of those "universal graveyards" really exist, and as a class they are called lagerstätten.
Lagerstätten is a German word that means "resting places," only recently borrowed by geologists. A lagerstatte is a spectacular rarity, and a few dozen of them are scattered through the Earth's geologic record like gems.
You've probably heard of some lagerstätten. One is the Tar Pits of Rancho La Brea, in Los Angeles, where sabertooth cats and many other recently extinct creatures are fossilized by the hundreds. Another is the Burgess Shale in the Canadian Rockies. Europe has several, including the Solnhofen Limestone where the famous dinosaur-bird Archaeopteryx was first found in all its feathered glory. And Australia has the extremely old and strange Precambrian fossils of the Ediacara Hills. All of these and more are represented on the Web, and I've built a growing list that brings them together.
Lagerstätten You Can Visit
Lagerstätten are a truly nonrenewable scientific resource, and they tend to come under government protection. The Burgess Shale, for instance, is strictly supervised by the Canadian national park system. The amazing rhino beds of Nebraska, where whole herds of Miocene mammals were buried by volcanic ash, are fenced inside Ashfall Fossil Beds State Historical Park. And the 525-million-year-old fossils of Chengjiang, with their exquisitely preserved internal details, are being placed under institutional control.
Others are more open. The English city of Dudley, site of the historic Rochester Shale and its beautiful "Dudley-bug" fossils from the Silurian Period, has campaigned to be named a geologic World Heritage Site. And in a rare exception to the small size of lagerstätten, the widespread Green River Formation in the Rocky Mountains is big enough for both the Fossil Butte National Monument and commercial dig-your-own fossil mines. You can buy a pretty Eocene-age Green River fossil fish at almost any rock show, with every rib of every fin preserved in the cream-colored claystone from the former lake bed.
The amount of detail in lagerstätten fossils is hard to believe. Fortunately Yale University has put some online, where you can zoom in on extreme close-ups of Permian dragonfly wings from Kansas or the baffling arthropod Waptia fieldensis from the Burgess Shale.
Making Sense of Lagerstätten
Lagerstätten are formed by unusually intense versions of common fossil-making processes. In one scenario, organisms die in a place where they are quickly covered and oxygen kept out. This may be enough in younger lagerstätten like the tar pits of La Brea. In others, mineralized fluids come equally quickly, and gently replace the organic remains, with the slow help of anaerobic organisms. Phosphates, pyrite and silica are the main minerals that take part.
Other lagerstätten preserve their fossils as thin, exquisitely detailed carbon films. The Green River beds are an example of this type. And the Ediacaran fossils appear to have a connection to the mats of microbes that once covered much of the seafloor in that low-oxygen world.
Lagerstätten are so special they can lure scientists into dangerous speculation, as if these luckily preserved bits of prehistory represented the whole world. For instance, the Chengjiang fossils show a diversity that is greater than anything found in more recent geologic history. But no way can biologist Paul Chien, who has studied them closely, claim that the Chengjiang fossils show creation by God and disprove evolution à la Darwin (here's his tendentious attempt, a 50-page PDF from the Discovery Institute). A single locality simply cannot support such a far-reaching conclusion. But that's science for you—it doesn't advance without a great many ideas being thrown up and tested against the evidence. Those ideas are usually imperfect . . . like the overwhelming majority of the world's fossils.
PS: A weird fossil critter from the Mazon Creek lagerstatte, the Tully Monster, has become the state fossil of Illinois.