Page Museum at the La Brea Tar Pits

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ScienceShot: Drowning in Tar, Eaten by Insects

The only thing worse than falling into an oozing pool of asphalt and having your bones ravaged by insects would be if you fell in and no one ever discovered your body. Fortunately for some of prehistory’s most important mammalian species, and for science, that didn’t happen at the famous La Brea Tar Pits in Los Angeles. Thousands of bones of mastodons, saber-toothed cats, bison, camels, ground sloths, and horses have been uncovered in the pits over the years, to the delight of researchers and visiting schoolchildren. Now, scientists report in PLOS ONE that insect damage on the fossil bones can tell scientists a lot about when and how these animals died. The team exposed bones from chickens, pigs, and sheep to beetle species known to feed on rotting carcasses. The tiny jaws of the beetle larvae left telltale traces of chewing on the bones, which were then matched with similar traces found on fossils like this 35,000-foot bone of a prehistoric horse. (From fossil insects found in the tar pits, the team knew that these same insect species were around thousands of years ago.) Because some species of beetles attack bone only when it has already been worked over for many weeks by other insects, the researchers were able to estimate from the types of jaw marks that the animals had floated on the surface of the tar for 17 to 20 weeks before sinking and also that they had probably fallen in during warm months of spring and summer when these particular beetles are active.