Fossils preserved in sap offer an astonishingly clear view of the distant past, but they come at a high price. atthew Downen had never done anything like this before. In a hotel room in Santo Domingo, the capital of the Dominican Republic, he watched as a dealer poured a bag of amber fossils onto a white towel spread over a desk. The previous night, at the opening reception for the eighth International Conference on Fossil Insects, Arthropods, and Amber, Downen had gotten a tip from a friend: A guy here had spiders fossilized in amber, and he was looking for someone to take them. Downen, a doctoral student in entomology at the University of Kansas, was initially ecstatic. Spiders for free? He had come to the meeting to present his research on spider diversity in ancient lake beds; more fossilized spiders could expand his findings. When he expressed his enthusiasm, he was quickly introduced to a large, jovial dealer named Jorge, who showed him a smartphone photo of a spider with an unusually long abdomen. “He was like, ‘We’ve got all kinds of amber,’” Downen recalls. Jorge told Downen that if he was interested, he should meet him the next morning at 8—and bring cash. Downen reali...