Different elements of the fossil record disappear at different rates: Bone is lost at greater rates than terrestrial sediments, and that’s especially the case for the continental U.S. and South America, compared to the Arctic. The findings were published in Biology Letters last week.
When it comes to the fossil record, older things are generally less common than younger things. This progressive, time-dependent loss of geologic deposits is called taphonomic loss. And to make sure abundance is measured as actual abundance in the fossil record for a particular time period (relative to the abundance of geologic deposits of the same age), researchers turn to what’s called taphonomic correction.
To create models of taphonomic loss, University of Wyoming’s Todd Surovell and Spencer Pelton compiled hundreds of radiocarbon dates on bones of extinct Pleistocene fauna from South America, the contiguous U.S., and eastern Beringia (near the Bering Strait between Russia and Alaska) that date back to between 13,000 and 40,000 years.
The duo found that bone is lost at greater rates than terrestrial sediments overall – but only for South America and the non-arctic regions of the U.S. Bone in eastern Beringia was lost at approximately the same rate as terrestrial sediments, thanks to the excellent preservation effects of permafrost. “Considerably more bone has been lost over time in regions farther south – in fact, at a faster rate than the sediments in which they were deposited have eroded," Surovell says in a statement. "That means researchers must adjust for those differences as they estimate the numbers of these animals, many of which are now extinct, across the Americas."
For the 10,000-year period from 25,000 to 15,000 years ago, their eastern Beringia bone model indicated an approximately 47 percent loss of material, while for the South America and contiguous U.S. bones, their models found a 93 to 99 percent loss. That means, 100 fossils dating back 25,000 years from Alaska would be equivalent in abundance to about 189 fossils dating back 15,000 years; for South America and farther south in the U.S., 100 25,000-year-old fossils are equivalent to more than 3,000 fossils at 15,000 years before present.