Filling gaps in the primate record
The researchers were hunting fossils dating to the late Paleocene and early Eocene epochs, about 55 million to 50 million years ago, when the Rocky Mountains were first rising and the climate was significantly warmer and wetter on average than today. Back then a large freshwater lake dominated the dig region, with streams flowing to it from the surrounding mountains. The area was home to crocodiles, turtles, lizards, fish and lots of mammals, including very primitive rodents, horses and bats as well as primates similar to modern lemurs, tarsiers, lorises and galagos.
Today, the area is mostly dry sagebrush scarred and pocked with gullies, buttes and dunes. Pronghorn antelope run alongside cars and groups of elk occasionally dash in front of them. Roaming stallions greet campers in the morning with thunderous snorts, and falcons occasionally dive at the visitors to keep them away from nests. The area seems mercifully free of venomous snakes, but thunderstorms can destroy tents and clog trails with slippery mud that can trap a truck.
Scientists have worked in this desert since 1994 and have unearthed roughly 10,000 mammalian fossils from the 100 localities now known. Even so, "this basin has been a blank mark on the map for a long time when it comes to ancient primates," remarks paleontologist Brett Nachman of the University of Texas at Austin. Many more mammalian fossils are needed.
Anemone's neural network pointed out several places to search. Initially, these proved fruitless—the scientists unearthed many fossils at the first recommended sites, but not the kind they wanted. The researchers had the neural network search for fossils in areas that past geologic surveys declared were in the Wasatch Formation—former lakeshore and riverside areas where they expected to unearth primate fossils. But on arrival at the first dozen or so sites, it was clear the original surveys were in error. Instead, those locations were actually in the Green River Formation—former lakebed areas with many aquatic fossils but few mammal bones.
On the next-to-last day of field work this past summer, however, the researchers looked at three more suggested sites, ones they were sure were located in the Wasatch Formation. After hiking for about an hour across the seemingly flat desert, they came across boulder-strewn hollows where they uncovered a cache of mammalian fossils, including teeth from the extinct five-toed horse Hyracotherium.
"This is the first successful test of an artificial neural network to find fossils," Anemone says. "It led us right through the sagebrush."
Intriguingly, these three sites were depressions in the soil that were all but invisible from a distance on the ground, unlike the hills the researchers normally inspect for fossils. "We would never have found these sites without the neural network—they're so out of the way and hidden," Anemone says. "I was worried about whether the neural network would work," he adds. "It sure felt good pulling those fossils out."
Beyond the black box
Fleagle cautioned that neural networks are essentially black boxes—one could never be sure how the systems arrive at their findings. "It would be good to know what features the algorithm is actually using to identify the fossil areas," he says. "Are they the same features that a geologist could also identify from a map or in the field?"
As a result, scientists see the neural networks only as stepping-stones to a more analytical approach to fossil hunting. In fact, Anemone and his colleagues are now directly scanning how fossil sites appear in visible and infrared light in the hope they can predict for themselves how these locations might differ from other areas. Besides the Great Divide Basin, they hope to conduct such research in Africa, possibly helping to look for fossils of monkeys or even early hominids.