Notes

A range of animal and plant specimens that became entrapped and were then preserved in tar pits have been removed and studied so that researchers can learn about the past. The Rancho La Brea tar pits located near Los Angeles in southern California are a collection of pits of sticky asphalt deposits that differ in deposition time from 40,000 – 12,000 YBP. Commencing 40,000 YBP, trapped asphalt has been moved through fissures to the surface by methane pressure, forming seeps that can cover several square meters and be 9–11 metres (30–36 ft) deep.[36] Over 200,000 specimens (mostly fragments) have been recovered from the tar pits,[19] with the remains ranging from saber-toothed cats to squirrels, invertebrates, and plants.[36] The time period represented in the pits includes the Last Glacial Maximum when global temperatures were 8 °C (46 °F) lower than today, the Pleistocene–Holocene transition (Bølling-Allerød interval), the Oldest Dryas cooling, the Younger Dryas cooling from 12,800 – 11,500 YBP, and the American megafaunal extinction event 12,700 YBP when 90 genera of mammals weighing over 44 kilograms (97 lb) became extinct.[37][53]

Isotope analysis can be used to identify some chemical elements, allowing researchers to make inferences about the diet of the species found in the pits. An isotope analysis of bone collagen extracted from La Brea specimens provides evidence that C. dirus, the saber-toothed cat (Smilodon fatalis), and the American lion (Panthera leo atrox) competed for the same prey. Their prey included "Yesterday's camel" (Camelops hesternus), the Pleistocene bison (Bison antiquus), the "dwarf" pronghorn (Capromeryx minor), the western horse (Equus occidentalis), and the "grazing" ground sloth (Paramylodon harlani) native to North American grasslands. The Columbian mammoth (Mammuthus columbi) and the American mastodon (Mammut americanum) were rare at La Brea. The horses remained mixed feeders and the pronghorns mixed browsers, but at the Last Glacial Maximum and its associated shift in vegetation the camels and bison were forced to rely more heavily on conifers.[57]

A study of isotope data of La Brea C. dirus fossils dated 10,000 YBP provides evidence that the horse was at that time an important prey species, and that sloth, mastodon, bison, and camel were less common in the C. dirus diet.[50][59] This indicates that C. dirus was not a prey specialist, and at the close of the late Pleistocene before its extinction it was hunting or scavenging off the most available herbivores.[59]