La Brea Tar Pits is an active paleontological research site in urban Los Angeles. Hancock Park was formed around a group of tar pits where natural asphalt (also called asphaltum, bitumen, or pitch; brea in Spanish) has seeped up from the ground for tens of thousands of years. Over many centuries, the bones of trapped animals have been preserved. The George C. Page Museum is dedicated to researching the tar pits and displaying specimens from the animals that died there. La Brea Tar Pits is a registered National Natural Landmark.
Illustration of several species getting mired in the tar pits
Tar pits are composed of heavy oil fractions called gilsonite, which seeps from the Earth as oil. Crude oil seeps up along the 6th Street Fault from the Salt Lake Oil Field, which underlies much of the Fairfax District north of Hancock Park.[2] The oil reaches the surface and forms pools, becoming asphalt as the lighter fractions of the petroleum biodegrade or evaporate.[3] The asphalt then normally hardens into stubby mounds. The pools and mounds can be seen in several areas of the park.
This seepage has been happening for tens of thousands of years, during which the asphalt sometimes formed a deposit thick enough to trap animals. The deposit would become covered over with water, dust, or leaves. Animals would wander in, become trapped, and die. Predators would enter to eat the trapped animals and would also become stuck. As the bones of a dead animal sink, the asphalt soaks into them, turning them dark-brown or black in color. Lighter fractions of petroleum evaporate from the asphalt, leaving a more solid substance, which then encases the bones. Dramatic fossils of large mammals have been extricated but the asphalt also preserves microfossils: wood and plant remnants, rodent bones, insects, mollusks, dust, seeds, leaves, and pollen grains.[4] Examples of some of these are on display in the George C. Page Museum. Radiometric dating of preserved wood and bones has given an age of 38,000 years for the oldest known material from the La Brea seeps.
History
The Tar Pits in 1910. Oil derricks can be seen in the background.
The Native American Chumash and Tongva people living in the area built boats unlike any others in North America. Pulling fallen Northern California redwood trunks and pieces of driftwood from the Santa Barbara Channel, their ancestors learned to seal the cracks between the boards of the large wooden plank canoes by using the natural resource of tar. This innovative form of transportation allowed access up and down the coastline and to the Channel Islands. The Portolá expedition, a group of Spanish explorers led by Gaspar de Portolá, made the first written record of the tar pits in 1769. Father Juan Crespí wrote,
While crossing the basin, the scouts reported having seen some geysers of tar issuing from the ground like springs; it boils up molten, and the water runs to one side and the tar to the other. The scouts reported that they had come across many of these springs and had seen large swamps of them, enough, they said, to caulk many vessels. We were not so lucky ourselves as to see these tar geysers, much though we wished it; as it was some distance out of the way we were to take, the Governor [Portolá] did not want us to go past them. We christened them Los Volcanes de Brea [the Tar Volcanoes].[5]
Harrison Rogers, who accompanied Jedediah Smith on his 1826 expedition to California, was shown a piece of the solidified asphalt while at Mission San Gabriel, and noted in his journal, "The Citizens of the Country make great use of it to pitch the roofs of their houses".[6]
The La Brea Tar Pits and Hancock Park are situated within what was once the Mexican land grant of Rancho La Brea. For some years, tar-covered bones were found on the Rancho La Brea property, but were not initially recognized as fossils because the ranch had lost various animals–including horses, cattle, dogs, and even camels–whose bones closely resemble several of the fossil species. The original Rancho La Brea land grant stipulated that the tar pits be open to the public for the use of the local Pueblo. Initially, they mistook the bones in the pits for the remains of pronghorn (Antilocapra americana) or cattle that had become mired.
Early excavation (c.1913– c.1915)
In 1886, the first excavation for land pitch in the village of La Brea was undertaken by Messrs Turnbull, Stewart & co..[7]
Union Oil geologist W. W. Orcutt is credited, in 1901, with first recognizing that fossilized prehistoric animal bones were preserved in pools of asphalt on the Hancock Ranch. In commemoration of Orcutt's initial discovery, paleontologists named the La Brea coyote (Canis latrans orcutti) in his honor.[8]
Contemporary excavations of the bones started in 1913–1915. In the 1940s and 1950s, public excitement was generated by the preparation of previously recovered large mammal bones.[9] A subsequent study demonstrated the fossil vertebrate material was well preserved, with little evidence of bacterial degradation of bone protein.[10] They are believed to be some 10–20,000 years old, dating from the last glacial period.[11]
Excavation of "Project 23" and newly uncovered pits
2011 VOA report about the new discoveries in the pits
On February 18, 2009, George C. Page Museum announced the 2006 discovery of 16 fossil deposits that had been removed from the ground during the construction of an underground parking garage for the Los Angeles County Museum of Art next to the tar pits.[12] Among the finds are remains of a saber-toothed cat, dire wolves, bison, horses, a giant ground sloth, turtles, snails, clams, millipedes, fish, gophers, and an American lion.[12][13] Also discovered is a nearly intact mammoth skeleton, nicknamed Zed; the only pieces missing are a rear leg, a vertebra, and the top of its skull, which was sheared off by construction equipment in preparation to build the parking structure.[13][14][15]
These fossils were packaged in boxes at the construction site and moved to a compound behind Pit 91, on Page Museum property, so that construction could continue. Twenty-three large accumulations of tar and specimens were taken to the Page Museum. These deposits are worked on under the name "Project 23". As work for the public transit D Line is extended, museum researchers know more tar pits will be uncovered, for example near the intersection of Wilshire and Curson.[12] In an exploratory subway dig in 2014 on the Miracle Mile, prehistoric objects unearthed included geoducks, sand dollars, and a 10-foot limb (3.0m) from a pine tree, of a type now found in Central California's woodlands.[16]
George C. Page Museum
The La Brea Tar Pits Museum in Hancock Park
In 1913, George Allan Hancock, the owner of Rancho La Brea, granted the Natural History Museum of Los Angeles County exclusive excavation rights at the Tar Pits for two years. In those two years, the museum was able to extract 750,000 specimens at 96 sites, guaranteeing that a large collection of fossils would remain consolidated and available to the community.[17] Then in 1924, Hancock donated 23 acres (9.3ha) to LA County with the stipulation that the county provide for the preservation of the park and the exhibition of fossils found there.[17]
The George C. Page Museum of La Brea Discoveries, part of the Natural History Museum of Los Angeles County, was built next to the tar pits in Hancock Park on Wilshire Boulevard. Construction began in 1975, and the museum opened to the public in 1977.[18] The area is part of urban Los Angeles in the Miracle Mile District.
The museum tells the story of the tar pits and presents specimens excavated from them. Visitors can walk around the park and see the tar pits. On the grounds of the park are life-sized models of prehistoric animals in or near the tar pits. Of more than 100 pits, only Pit 91 is still regularly excavated by researchers and can be seen at the Pit 91 viewing station. In addition to Pit 91, the one other ongoing excavation is called "Project 23". Paleontologists supervise and direct the work of volunteers at both sites.[19]
In respect of it being the 'richest paleontological site on Earth for terrestrial fossils of late Quaternary age', the International Union of Geological Sciences (IUGS) included the 'Late Quaternary asphalt seeps and paleontological site of La Brea Tar Pits' in its assemblage of 100 'geological heritage sites' around the world in a listing published in October 2022. The organisation defines an IUGS Geological Heritage Site as 'a key place with geological elements and/or processes of international scientific relevance, used as a reference, and/or with a substantial contribution to the development of geological sciences through history.'[21]
The park is known for producing myriad mammalfossils dating from the last glacial period. While mammal fossils generate significant interest, other fossils, including fossilized insects and plants, and even pollen grains, are also valued. These fossils help define a picture of what is thought to have been a cooler, moister climate in the Los Angeles basin during the glacial age. Microfossils are retrieved from the matrix of asphalt and sandy clay by washing with a solvent to remove the petroleum, then picking through the remains under a high-powered lens.
Historically, the majority of the mammals excavated from the La Brea deposits had been large carnivores, supporting a hypothesized "carnivore trap" in which large herbivores entrapped in asphalt attracted predators and scavengers which then became entrapped while trying to steal a quick meal. However, new research with an eye towards microfossils has revealed a stunning diversity and abundance of many types of mammals. According to palentologist Thomas Halliday, "Rancho La Brea Tar Pits... where big herbivores typically get stuck in tar which naturally seeps from the ground, and as a result, you get huge concentrations of just specifically herbivores. You get a herbivorous sample of the ecosystem and very few carnivores, except those that are trying to scavenge on the already dead carcasses that have just got stuck in the tar."[22][23][24][25][26]
Bacteria
Methane gas escapes from the tar pits, causing bubbles that make the asphalt appear to boil. Asphalt and methane appear under surrounding buildings and require special operations for removal to prevent the weakening of building foundations. In 2007, researchers from UC Riverside discovered that the bubbles were caused by hardy forms of bacteria embedded in the natural asphalt. After consuming petroleum, the bacteria release methane. Around 200 to 300 species of bacteria were newly discovered here.[27]
Human presence
Only one human has been found, a partial skeleton of the La Brea Woman[28] dated to around 10,000 calendar years (about 9,000 radiocarbon years) BP,[29] who was 17 to 25 years old at death[30] and found associated with remains of a domestic dog, so was interpreted to have been ceremonially interred.[31] In 2016, however, the dog was determined to be much younger in date.[32]
Also, some even older fossils showed possible tool marks, indicating humans active in the area at the time. Bones of saber-toothed cats from La Brea showing signs of "artificial" cut marks at oblique angles to the long axis of each bone were radiocarbon dated to 15,200 ± 800 B.P. (uncalibrated).[33]
If these cuts are in fact tool marks resultant from butchering activities, then this material would provide the earliest solid evidence for human association with the Los Angeles Basin. Yet it is also possible that there was some residual contamination of the material as a result of saturation by asphaltum, influencing the radiocarbon dates.[34]
Gallery
Tar and wild flower run within La Brea campus (2014)
Skeleton of a Columbian mammoth from the tar pits, displayed in the George C. Page Museum
Smilodon is a genus of the extinct machairodont subfamily of the felids. It is one of the best known saber-toothed predators and most famous prehistoric mammals. Although commonly known as the saber-toothed tiger, it was not closely related to the tiger or other modern cats. Smilodon lived in the Americas during the Pleistocene epoch. The genus was named in 1842 based on fossils from Brazil; the generic name means "scalpel" or "two-edged knife" combined with "tooth". Three species are recognized today: S. gracilis, S. fatalis, and S. populator. The two latter species were probably descended from S. gracilis, which itself probably evolved from Megantereon. The hundreds of individuals obtained from the La Brea Tar Pits in Los Angeles constitute the largest collection of Smilodon fossils.
Tar pits, sometimes referred to as asphalt pits, are large asphalt deposits. They form in the presence of oil, which is created when decayed organic matter is subjected to pressure underground. If this crude oil seeps upward via fractures, conduits, or porous sedimentary rock layers, it may pool up at the surface. The lighter components of the crude oil evaporate into the atmosphere, leaving behind a black, sticky asphalt. Tar pits are often excavated because they contain large fossil collections.
The dire wolf is an extinct canine. It is one of the most famous prehistoric carnivores in North America, along with its extinct competitor Smilodon. The dire wolf lived in the Americas and eastern Asia during the Late Pleistocene and Early Holocene epochs. The species was named in 1858, four years after the first specimen had been found. Two subspecies are recognized: Aenocyon dirus guildayi and Aenocyon dirus dirus. The largest collection of its fossils has been obtained from the Rancho La Brea Tar Pits in Los Angeles.
The Natural History Museum of Los Angeles County is the largest natural and historical museum in the western United States. Its collections include nearly 35 million specimens and artifacts and cover 4.5 billion years of history. This large collection is comprised not only of specimens for exhibition, but also of vast research collections housed on and offsite.
Gymnogyps is a genus of New World vultures in the family Cathartidae. There are five known species in the genus, with only one being extant, the California condor.
Rancho La Brea was a 4,439-acre (17.96 km2) Mexican land grant in present-day Los Angeles County, California, given in 1828 to Antonio Jose Rocha and Nemisio Dominguez by José Antonio Carrillo, the alcalde of Los Angeles. Rancho La Brea consisted of one square league of land of what is now Wilshire's Miracle Mile, Hollywood, and parts of West Hollywood. The grant included the famous La Brea Tar Pits.
Hancock Park is a city park in the Miracle Mile section of the Mid-Wilshire neighborhood in Los Angeles, California.
Teratornis was a genus of huge North American birds of prey—the best-known of the teratorns—of which, two species are known to have existed: Teratornis merriami and Teratornis woodburnensis. A large number of fossil and subfossil bones, representing more than 100 individuals, have been found in locations in California, Oregon, southern Nevada, Arizona, and Florida, though most are from the Californian La Brea Tar Pits. All remains except one Early Pleistocene partial skeleton from the Leisey Shell Pit near Charlotte Harbor, Florida date from the Late Pleistocene, with the youngest remains dating from the Pleistocene–Holocene boundary.
The McKittrick Tar Pits are a series of natural asphalt lakes situated in the western part of Kern County in southern California. The pits are the most extensive asphalt lakes in the state.
The Carpinteria Tar Pits are a series of natural asphalt lakes situated in the southern part of Santa Barbara County in southern California, USA.
La Brea Woman is a human whose remains were found in the La Brea Tar Pits in Los Angeles, California. The remains, first discovered in the pits in 1914, are the partial skeleton of a woman. At around 18–25 years of age at death, she has been dated at 10,220–10,250 years BP. These are the only human remains to have ever been discovered at the La Brea Tar Pits.
Grus pagei is an extinct crane reported from the upper Pleistocene asphalt deposits of Rancho La Brea, Los Angeles, California. It is one of three cranes present at Rancho La Brea, the others being the living whooping crane and sandhill crane. It is the smallest of the three cranes, and it had a relatively longer, more slender skull than the living cranes. At least 11 individuals are represented by 42 fossil bones. Described by Kenneth E. Campbell Jr. in 1995, it was named after the philanthropist responsible for the museum at the tar pits, George C. Page.
William Warren Orcutt was a petroleum geologist who is considered a pioneer in the development of oil production in California, and the use of geology in the oil industry. He is also known for his contributions to paleontology, which brought the fossils of the La Brea Tar Pits to the attention of the scientific community.
The Binagadi asphalt lake are a cluster of tar pits in urban Baku, Azerbaijan. Asphaltum or tar has seeped up from the ground in this area for tens of thousands of years. The tar is often covered with dust, leaves, or water. Over many centuries, animals that were trapped in the tar were preserved as bones.
Paleontology in California refers to paleontologist research occurring within or conducted by people from the U.S. state of California. California contains rocks of almost every age from the Precambrian to the Recent. Precambrian fossils are present but rare in California.
Paleontology in the United States refers to paleontological research occurring within or conducted by people from the United States. Paleontologists have found that at the start of the Paleozoic era, what is now "North" America was actually in the southern hemisphere. Marine life flourished in the country's many seas. Later the seas were largely replaced by swamps, home to amphibians and early reptiles. When the continents had assembled into Pangaea drier conditions prevailed. The evolutionary precursors to mammals dominated the country until a mass extinction event ended their reign.
Hildegarde Howard was an American pioneer in paleornithology, mentored by the famous ornithologist, Joseph Grinnell, at the Museum of Vertebrate Zoology (MVZ) and in avian paleontology. She was well known for her discoveries in the La Brea Tar Pits, among them the Rancho La Brea eagles. She also discovered and described Pleistocene flightless waterfowl at the prehistoric Ballona wetlands of coastal Los Angeles County at Playa del Rey. In 1953, Howard became the third woman to be awarded the Brewster Medal. She was also the first woman president of the Southern California Academy of Sciences. Hildegarde, throughout her career wrote 150 papers.
A list of prehistoric and extinct species whose fossils have been found in the La Brea Tar Pits, located in present-day Hancock Park, a city park on the Miracle Mile section of the Mid-Wilshire district in Los Angeles, California.
Capromeryx was a genus of dwarf pronghorns (Antilocapridae) that originated in North America during the Pliocene about 5 million years ago. The closest living relative and only surviving member of the family is the North American pronghorn.
References
↑ "Hancock Park". Office of Historic Preservation, California State Parks. Retrieved October 7, 2012.
↑ Khilyuk, Leonid F.; Chilingar, George V. (2000). Gas migration: events preceding earthquakes. Gulf Professional Publishing. p.389. ISBN0-88415-430-0.
↑ Smith, J. S., & Brooks, G. R. (1977). The Southwest expedition of Jedediah S. Smith: His personal account of the journey to California, 1826–1827. Glendale, Calif: A. H. Clark, p. 239. ISBN0-8706-2123-8
↑ Mineral Resources of the United States. (1894). United States: U.S. Government Printing Office.
↑ Page Museum. "About the museum". Page Museum web site. The Natural History Museum of Los Angeles County Foundation. Retrieved January 25, 2016.
↑ Page Museum. "Page Museum—La Brea Tar Pits". Page Museum web site. The Natural History Museum of Los Angeles County Foundation. Retrieved December 15, 2006.
↑ J.C. Merriam (1914) Preliminary report on the discovery of human remains in an asphalt deposit at Rancho La Brea, Science 40: 197–203
↑ F.R. O'Keefe, E.V. Fet, and J.M. Harris (2009) Compilation, calibration, and synthesis of faunal and floral radiocarbon dates, Rancho La Brea, California, Contributions in Science 518: 1–16
↑ G.E. Kennedy (1989) A note on the ontogenetic age of the Rancho La Brea hominid, Los Angeles, California, Bulletin, Southern California Academy of Sciences 88(3): 123–26
↑ R.L. Reynolds (1985) Domestic dog associated with human remains at Rancho La Brea, Bulletin, Southern California Academy of Sciences 84(2): 76–85
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