21 December 2015

21. Rancho La Brea

Dire Wolf Skulls
Page Museum
Location: California, USA
Age: Pleistocene-Holocene (55,000 years ago-Recent)

Many Cenozoic lagerstätten have produced more fossils (Fossil Lake, for example) and many have higher quality of preservation (such as Messel), but none is as widely known as the "tar pits" of Rancho La Brea.  Part of the reason for this fame is likely the location of the site, on Wilshire Boulevard in the middle of Los Angeles.  Part of it is due to the unusual method of preservation, in which animals were trapped and eventually buried in asphalt seeps.  The bulk of La Brea's fame, though, is due to the fossils uncovered there, which include megafaunal mainstays - mammoths, sloths, camels, and horses - as well as rarer large mammals, such as tapirs, and a wide variety of small-bodied animals.  The most spectacular fossils from La Brea are its predators, which are found in huge numbers (in the thousands, in the case of especially common species).  Coyotes (originally described as their own species, Canis orcutti, sadly no longer recognized as distinct from the living C. latrans) and dire wolves are particularly abundant, as is Smilodon, the saber-toothed cat that has such wide appeal that it was designated California's state fossil.  Other big predators that show up at Rancho La Brea include the extinct American lion Panthera atrox, the scimitar-toothed cat Homotherium, and the giant short-faced bear Arctodus, as well as still-living predators such as cougars, timber wolves, and black bears.  It's not just mammalian predators that are abundant at the site: a wide variety of raptors have been found here in larger numbers that anywhere else, including familiar taxa such as hawks, eagles, and condors, but also the extinct Teratornis (which besides being impressive in and of itself, has a fantastic name that translates as "Monster Bird").  Why so many predators?  It's long been hypothesized that prey animals trapped in asphalt would have served as lures for carnivorous animals, many of which would have then become trapped themselves, providing ever more carrion to be had.  Recent research (including, at the risk of indulging in self-promotion, some of my own) has supported this hypothesis, further suggesting that the abundance of large and/or social predators at La Brea implies that animals particularly adept at defending carcasses from other scavengers were frequently preserved at the site.  This is just one example of how Rancho La Brea fossils have been used to reconstruct the biology of Pleistocene organisms.  Other long-standing areas of study have been whether or not Smilodon was social (a highly unusual trait among living cats) and, more relevant to the theme I've been following all month, how climate change through the Pleistocene and Holocene have affected the La Brea biota.

Visit: The LA area is home to several of the world's great museums, and even among that distinguished milieu, the George C. Page Museum of La Brea Discoveries in Hancock Park is a standout.  Besides the museum itself, several asphalt pools, excavation sites, and megafaunal statues are on view in the park.
Fossils: Almost every major natural history museum has a few Rancho La Brea specimens.  The Page Museum is the best spot to see them in the LA area, but several specimens are on display at its parent museum, the LA County Museum, as well.
Is there a relevant book full of gorgeous fossil photos that I can gift to a paleontologically-minded friend?: There is!

This post is part of my 2015 Paleontology Advent Calendar, a series of vignettes on lagerstätten - sites of exceptional fossil preservation - that document changes in climate and environments through the Cenozoic.  You can see the other posts here.

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