Anthropology

    The natural asphalt deposits at Rancho La Brea, more commonly known as the La Brea Tar Pits, have produced hundreds of thousands of fossils since geological investigations began in 1901. In 1875, Rancho owner Major Henry Hancock noticed that ancient bones were occasionally turned up as customers hauled away brea for their personal use.  More extensive geological investigations from 1913 to 1915 established the archaeological importance of the site, and the area was re-established as Hancock Park in order to preserve the tar pits for an interested public and scientific community. The Page Museum of La Brea Discoveries, established in 1977, displays fossils retrieved from the tar pits and educates visitors on more general principles of geology. 

    The majority of plants and animals preserved as fossils at Rancho La Brea are from the later Pleistocene epoch, approximately 10,000 to 40,000 years ago.  Visitors to the Page Museum are reminded that this period is relatively late in terms of geologic time, coming nearly 65 million years after the extinction of the dinosaurs.  Radiometric dating has been used to establish the age of the fossils recovered.  The most successful method of radiometric dating used at La Brea has measured the reversion to nitrogen of carbon-14, a radioactive isotope whose half-life is 5,370 years. 

    Fossils have been preserved remarkably well at La Brea.  Rapid sedimentation at the site, taking place over thousands of years, kept a great deal of organic material from succumbing to decay.  The asphalt that seeped to the surface through ancient stream channel deposits, creating puddles of tar, is responsible for the wealth of fossils found at the site.  Animals were often trapped in these tar puddles deceptively covered with leaves and a layer of dirt. Once trapped, these animals would lure larger predators and scavengers to the area, leading to further entrapment.  As the bones of trapped animals rotted free from soft tissue they were saturated with asphalt and began to settle in the mire.  Cool winters solidified the tar and allowed layers of sediment to accumulate.  Warm summers allowed asphalt to flow in and reset the animal trap.  While the movement of sediment and asphalt allowed for the high-quality preservation of individual bones, it also served to mix fossils together, making complete skeletons exceedingly rare.  The churning of the asphalt also produces what is known as pit wear, holes and grooves made in bones as they rub together (Harris 13).

    Early excavations focused on recovering large and more spectacular mammals from the mire while the microfossils that could have told scientists a great deal about the Pleistocene climate and flora were largely ignored (Harris 15).  In 1969 a Natural History Museum excavation of Pit 91 endeavored to collect those important microfossils.  Fossils of more than 140 species of plants and 400 species of animals have now been recovered. Many extinct animals have been reconstructed from bones gathered from La Brea, but microfossils have also helped to paint a picture of the ecosystem and climate of the Los Angeles area 40,000 years ago.  Perhaps surprisingly, the Ice Age climate of Los Angeles was much as it is now, only slightly more humid and lacking the extreme heat the area often experiences today.  The remains of La Brea flora, consisting mainly of drought-tolerant scrub brush, have shed a great deal of light on the Pleistocene climate in the region.  Ecological patterns can be surmised from the Chaparral commonly found at the site, as it depends on fire to thrive.  

    The fossils recovered from La Brea show that the glaciers and ice sheets often associated with the Ice Age were not present in this region.  One hundred thousand years ago, Rancho La Brea lay well below the surface of the Pacific Ocean.  The sea retreated as the last age of glaciation began, and stream erosion of the Hollywood Hills made for heavy sedimentation.  Crude oil has been seeping up from the earths surface in the La Brea area for the past 40,000 years.  Biologists and paleontologists have been comparing the fossils of animals found in La Brea with their closest living relatives in order to form a clearer understanding of climatic and environmental changes over millennia.  The fauna of the region are well documented by excavations at La Brea.

    Perhaps the most famous find at La Brea is the skull and partial skeleton of La Brea Woman, the only human remains found in the pits.  Various theories have been proposed to explain the presence of her remains. Her fractured skull has led some to speculate that she was murdered by a blow to the head and her body dumped in a shallow tar pool (Harris 24). Less speculative anatomical studies show that the remains of the 20-25 year-old woman are nearly 9,000 years old, and that she has the worn teeth of someone accustomed to a diet of stone-ground meal.

    Le Brea is also well known for the remains of the Imperial Mammoth and American Mastodons on display at Page Museum, both of which are, of course, extinct.  Reconstructions of Imperial Mammoth skeletons show that the animal could stand nearly 13 feet tall and weigh close to 10,000 pounds.  Evidence of the of history of the mastodon familys migration, lineage, and relationship to its distant relative, the elephant, are also confirmed by La Brea fossils.  Forty-five million years ago, the mastodon family appeared in Africa, though mastodons reached North America only 15 million years ago during the Middle Miocene.  Mammoths, much smaller than mastodons, are more closely related to Indian and African elephants, as similarities in the teeth of the fossils recovered at La Brea show.  Mammoths and elephants migrated from Africa 5 million years ago, though only the mammoth reached the Americas.

    If the Natural History Museum of Los Angeles is to be believed, the saber-toothed cat most vividly captures the imagination of park visitors (Harris 46).  The remains of the fearsome creature have been named the official state fossil of California and are the second most commonly recovered fossil from La Brea.  The dagger-like teeth protruding from the jaw of the saber-toothed cat seem to indicate a gruesome hunting and killing process.  The fossil evidence at sites such as La Brea has led some scientists to conclude, however, that the large canine teeth were used to slash open the underbelly of captured prey, and not actually to kill (Harris 47). The biomechanics of this process can only be understood from well-preserved fossils such as those found at La Brea.  

    The fossil remains of mammoths, mastodons, and saber-toothed cats at La Brea are the mysterious record of a distant extinction event occurring roughly 11,000 years ago, though there is evidence of extinctions as recently as 8,000 years ago.  The reason for the extinctions are a matter of considerable debate (Harris 75).  The presence of humans, and human predation, is a likely contributor to the extinctions.  Climatic shifts are also thought to have first caused the extinction of herbivores and then the large carnivores who preyed on them.  The spectacular preservation of La Brea fossils, in many cases retaining fragments of food in animals teeth, has provided valuable information needed to shed light on the extinction mystery.

    Even after decades of research, the La Brea asphalt deposits continue to provide new discoveries.  In 2009, researchers from  Page Museum launched Project 23, hoping to usher in a new era of research and discovery (Science Daily).  The project uncovered the first complete mammoth found at Rancho La Brea, a creature the scientists nicknamed Zed. Scientists have halted excavations at Pit 91 (mentioned above) to focus on Project 23.  A new exhibit of La Brea fossils is planned for 2010, and researchers continue to learn about changes in Pleistocene flora, fauna, and climate.