The La Brea tar pits in Los Angeles—actually seeps of smelly asphaltum—are loaded with fossils. New analyses of chemicals inside their ancient teeth give clues as to what they ate and maybe why some of them went extinct.

The scientific literature contains over 100 examples of original biomaterials in fossils.¹ These include a few decades’ worth of reports, using at least a few dozen independent techniques to target specific vertebrate biochemicals—such as the hardy protein collagen.