December 21. Saber-toothed cat

Smilodon, the famous saber-toothed cat, was not a tiger nor even closely related to tigers. They were felids, cats in general, but they branched off from the families that include all modern cats pretty early in the development of the feline families. They probably diverged sometime during the Miocene, more than 10 million years ago. 

Smilodon and dire wolves (drawing by Robert Horsfall, 1913)

Smilodon’s scientific name doesn’t mean “smiling tooth,” but rather comes from the Greek meaning “carving-knife tooth,” and they did certainly have huge sharp canine teeth up to 11 inches long. The animal was about the size of a lion, and was probably the last in a lineage of similar carnivorous animals. It lived during the glacial period, the Pleistocene Epoch, from about 2.5 million years ago until 10,000 years ago. We’ll talk a bit more about the Pleistocene extinction of the saber-toothed cat and other large animals in a few days. Smilodon is the state fossil of California.

Lots of Smilodon fossils have been found in the famous La Brea Tar Pits in Los Angeles, along with a hugely diverse fauna. The presumption is that animals were attracted to the tar mistaking it for water or simply crossed it inadvertently, and became trapped. The asphalt, the tar, in the tar pits, is basically a heavy oil, a natural seep that has been active for many thousands of years. Oil, migrating from depth, has reached the surface. The material is less fluid than most oil, but more fluid than, say, the tar sands of Alberta. It’s not really a surprise that we’d find oil through the spectrum of possibilities, from highly liquid to completely solid, as in oil shale. There is a real oil field at depth at the La Brea site, the Salt Lake Oil Field, where oil is trapped in Miocene and Pliocene sediments in anticlines and fault blocks. The buoyant oil continued to migrate upward along one fault to reach the surface and form the tar pits. The material is heavy and viscous because the volatile portions have evaporated at the surface, leaving the tar behind. Brea is Spanish for tar.

The oldest fossils in the La Brea Tar Pits date to about 38,000 years ago – and many of them are extinct. The assemblage is huge, and includes extinct bison species, llamas, cheetahs, bats, sloths, mastodons, more than 100 bird species, snakes, insects, and plants. It is truly a lagerstätte, one of those amazing places where fossils are preserved in extraordinary detail.

—Richard I. Gibson

Drawing of tar pits by Robert Bruce Horsfall, 1913 (public domain)