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| Smilodon Skull at La Brea Tar Pits |
In the heart of Los Angeles, surrounded by traffic, office towers and people carrying coffees of improbable complexity, the Earth is still bubbling.
Dark pools of natural asphalt rise through the ground at Hancock Park, methane breaks at the surface and the air carries the unmistakable scent of petroleum.
Beneath the lawns and walkways lies one of the richest Late Pleistocene fossil deposits on Earth.
Mammoths are here. Dire wolves are here. Sabre-toothed cats, enormous bison, ancient horses, camels, ground sloths, coyotes, birds, beetles, seeds, pollen and the delicate bones of tiny rodents are all here.
Not alive, mercifully, but preserved in extraordinary numbers beneath modern Los Angeles, where natural asphalt seeps have been trapping plants and animals for tens of thousands of years.
The La Brea Tar Pits do not record one terrible day. They contain the accumulated evidence of countless separate accidents repeated across millennia. One animal became trapped, another arrived to investigate and several more approached because the Ice Age had not yet developed adequate warning signage.
FIRST, THEY ARE NOT ACTUALLY TAR PITS
The substance at La Brea is more accurately called natural asphalt, asphaltum or bitumen. Tar is generally produced by heating organic materials such as wood or coal, while asphalt is a naturally occurring petroleum substance. The familiar name has nevertheless stuck, which seems appropriate under the circumstances.
There is also a pleasing redundancy in “La Brea Tar Pits.” La brea means “the tar” in Spanish, making the full name roughly “the Tar Tar Pits.” We could insist upon calling them the La Brea Asphalt Seeps, but that would deprive palaeontology of a perfectly good geological tongue-twister.
Beneath the Los Angeles Basin are thick, oil-rich marine deposits laid down millions of years ago. Petroleum migrated upward through faults and fractures until it reached the surface. There, lighter components evaporated or were degraded by microorganisms, leaving the heavier and remarkably sticky asphalt behind.
This material did not necessarily form the enormous open pools often depicted in paintings and museum dioramas. Asphalt could seep into shallow depressions and spread across the ground, sometimes hidden beneath water, dust, leaves or sediment. To an approaching animal, the surface may have looked like ordinary damp soil or a harmless watering place.
The mistake would become apparent with the first step.
THE MAKING OF A PREDATOR TRAP
An asphalt seep did not need to be deep enough to swallow a mammoth whole. It needed only to be sticky enough to hold a foot. Once a hoof sank into the asphalt, the animal’s attempts to pull free could trap another limb. Struggling pressed the feet deeper, spread asphalt across hair and skin and rapidly exhausted the victim.
Large herbivores such as bison, horses, camels, mammoths and ground sloths occasionally became immobilized in this way. Their distress calls and movements attracted predators and scavengers.
A trapped bison represented a large meal that had already been thoughtfully restrained, and predators approached the opportunity with understandable enthusiasm and insufficient caution.
Dire wolves gathered. Sabre-toothed cats moved closer. Coyotes and scavenging birds arrived. Some fed from firmer ground, while others stepped onto the same deceptive surface and became trapped themselves.
This process is known as the predator-trap hypothesis, and it helps explain the remarkable abundance of carnivores in the La Brea deposits. One struggling herbivore could attract several predators and scavengers, producing a fossil assemblage in which carnivores greatly outnumber herbivores.
Roughly 70 to 80 per cent of the site’s larger mammal specimens are carnivores. That is almost the reverse of what we would expect in a living ecosystem, where herbivores generally outnumber large predators. The Natural History Museums of Los Angeles County notes that this carnivore-heavy composition distinguishes La Brea from most other fossil deposits.
This does not mean Ice Age Los Angeles was carpeted in dire wolves with the occasional bison squeezed between them. It means the asphalt seeps selectively trapped animals attracted to struggling prey. The deposit records not only which species lived in the region, but also how their behaviour influenced their likelihood of preservation.
The fossil record is rarely an impartial census. At La Brea, it is closer to a list of everyone who approached the buffet without first inspecting the floor.
DIRE WOLVES, SABRE-TOOTHED CATS AND ANCIENT COYOTES
Dire wolves were among the most frequently trapped large mammals. Known scientifically as Aenocyon dirus, they were heavily built canids that lived across the Americas during the Late Pleistocene. They had robust jaws and teeth suited to feeding on large prey, although, like living wolves, they probably scavenged when a meal presented itself.
Their abundance at La Brea may provide indirect evidence of social behaviour. If dire wolves hunted or scavenged in groups, one trapped herbivore might attract several pack members. A single incident could therefore add multiple wolves to the deposit. One meal, several hopeful carnivores and a deeply regrettable group decision.
The large collection allows researchers to study dire wolves as a population rather than as a scattering of isolated specimens. Individual animals can be compared for age, body size, tooth wear, injury and disease. Changes in anatomy and diet can also be tracked through time.
The most famous predator at La Brea is Smilodon fatalis, the sabre-toothed cat. If you have seen the skull and teeth of this kitty, you will agree the name is apt.
A fun fact and wee aside, Canada's first Smilodon was found in a drawer in a museum by Dr. Rufus Churcher when he was poking about an old collection in Alberta. A wonderful storyteller with a keen eye, we owe that man a lot.
It was not a tiger, despite the enduring popularity of the name “sabre-toothed tiger.” Smilodon belonged to an extinct branch of the cat family and had a body built quite differently from that of modern lions or tigers.
It possessed enormous upper canine teeth, exceptionally powerful forelimbs, a deep chest and a relatively short tail. Its jaw could open extraordinarily wide, allowing those elongated canines to be used without colliding with the lower jaw. Rather than pursuing prey over long distances, Smilodon was likely an ambush predator. Its muscular forelimbs may have helped restrain large prey while it delivered a carefully positioned bite.
This was important because the famous canine teeth, though formidable, were not indestructible. They were effective weapons but poor candidates for being driven casually into struggling bone. Even the Ice Age’s most dramatic dental arrangement required responsible handling.
La Brea specimens preserve evidence of arthritis, fractures, tooth damage and healing. Some animals survived serious injuries long enough for their bones to repair. This has raised intriguing questions about whether sabre-toothed cats lived socially and whether impaired individuals may have received food or protection from others.
Healing proves survival, but it does not automatically prove social care. An injured animal might have scavenged, selected smaller prey or simply endured. We must distinguish what a bone demonstrates from what it merely suggests. Still, the injuries reveal that these cats had individual histories. They aged, suffered accidents, recovered and continued living in a landscape filled with large prey, competing carnivores and treacherously sticky patches of ground.
Coyotes, Canis latrans, also occur abundantly at La Brea, but unlike dire wolves and sabre-toothed cats, they survived the end-Pleistocene extinction. Their ecological flexibility may have given them an advantage. Coyotes can eat mammals, insects, fruit, carrion and an impressive assortment of whatever else becomes available. They can occupy deserts, grasslands, woodlands, agricultural areas and cities.
Large specialists often thrive when their preferred prey and habitats are stable, but they can struggle when ecosystems change rapidly. Coyotes appear to have regarded climatic upheaval, megafaunal extinction and the eventual construction of Los Angeles as challenges requiring only minor adjustments.
They still live in the city today.
MAMMOTHS, MASTODONS AND CAMELS IN CALIFORNIA
The herbivores preserved at La Brea include ancient bison, horses, camels, deer, pronghorn, mammoths and mastodons. Together, they reveal a Southern California landscape quite different from the one we know today.
Columbian mammoths, Mammuthus columbi, were enormous members of the elephant family. They possessed long, curving tusks and high-crowned ridged teeth suited to processing abrasive vegetation. Their diets varied across environments and could include both grasses and other plants.
American mastodons, Mammut americanum, were shorter and more heavily built, with molar teeth bearing rounded cusps. These teeth were better suited to crushing leaves, twigs and branches. Mammoths and mastodons were related, but they were not interchangeable shaggy elephants wandering through identical habitats.
Their teeth record the difference rather elegantly. Mammoth molars resemble enormous washboards. Mastodon molars carry prominent rounded cusps, which gave the animal its name: “mastodon” refers to the breast-like shape of the tooth projections. Palaeontology occasionally arrives at terminology by routes we might not choose today.
One of the site’s remarkable discoveries is a largely complete Columbian mammoth nicknamed Zed. His remains were uncovered in 2006 during the construction of an underground parking facility beside the Los Angeles County Museum of Art. Zed is a reminder that major palaeontological discoveries do not always require an expedition to a distant desert. Sometimes they require a construction crew, a parking proposal and someone sensible enough to stop digging.
Ancient camels also lived in Ice Age California. The western camel, Camelops hesternus, was a large North American member of the camel family. This seems surprising only because we associate camels with Africa and Asia today. Camels actually evolved in North America and lived on the continent for tens of millions of years. Some migrated into Eurasia across Beringia, while others moved into South America and eventually gave rise to llamas, alpacas, guanacos and vicuñas.
The disappearance of camels from North America is the unusual part. Their presence at La Brea was perfectly ordinary at the time.
PROJECT 23: PALAEONTOLOGY BY WOODEN BOX
When construction near the Tar Pits encountered fossil deposits in 2006, excavating every specimen individually would have delayed work for an extremely long time. Instead, palaeontologists and engineers built large wooden crates around 23 fossil-bearing deposits. The blocks were lifted intact and moved to La Brea Tar Pits, where they could be excavated under controlled conditions.
The operation became known as Project 23.
Along with the boxed deposits came 327 buckets of fossil-rich sediment. The material contains large mammal bones, but also turtles, fish, snails, insects, seeds, leaves, small vertebrates and other remains essential to reconstructing the wider ecosystem. The museum’s Project 23 overview notes that researchers will be processing this enormous collection for years.
Project 23 demonstrates an important reality of modern palaeontology: fossil discovery frequently occurs during construction. Roads, foundations, mines and parking structures expose geological layers that would otherwise remain hidden. When scientific teams and developers work together, these unexpected discoveries can be recovered without sacrificing either the fossils or the project.
It also proves that if you place 23 enormous crates of asphalt-soaked Ice Age sediment in front of palaeontologists, they will be happily occupied for the foreseeable future.
THE TINY FOSSILS THAT RECONSTRUCT A LANDSCAPE
Mammoths and sabre-toothed cats attract attention, but some of La Brea’s most informative fossils are less than a centimetre long.
The asphalt and surrounding sediments preserve insects, spiders, seeds, leaves, pollen, molluscs, fish, frogs, lizards, bird bones, rodent teeth and tiny skeletal fragments. These remains are recovered from the excavated sediment, or matrix, which is carefully processed and examined under microscopes.
Staff and volunteers sort through it grain by grain. It is patient, meticulous work requiring steady hands and an ability to become sincerely delighted by something resembling a burnt sesame seed.
Microfossils allow researchers to reconstruct details that large mammal bones cannot provide. Pollen and seeds identify ancient vegetation. Beetles and other insects can indicate temperature, moisture and local habitat. Frogs and salamanders reveal the presence of freshwater or damp environments. Rodents can be sensitive indicators of particular ecological conditions.
The La Brea Fossil Lab emphasizes the importance of these small fossils for understanding environmental and climatic change during the Late Pleistocene.
Large mammals tell us who occupied the landscape. Microfossils tell us what the landscape was like.
Ice Age Los Angeles was not buried beneath a continental glacier. The region was generally cooler and wetter than it is today, with streams, grasslands, scrub and woodlands of oak and juniper. Mammoths, bison, horses and camels moved through these habitats while predators followed them.
It was recognizably Southern California, but with more water, fewer freeways and a substantial increase in large mammals capable of overturning your vehicle.
HOW ASPHALT PRESERVED THE FOSSILS
When animals became trapped, their bodies decayed and their bones sank into asphalt-rich sediment. Petroleum entered the pores of the bones, staining them dark brown or black and helping protect them from weathering and some forms of microbial destruction.
The asphalt also preserved delicate biological materials rarely retained at other fossil sites. These include bone collagen, plant cellulose and chitin from insect exoskeletons. Such materials can be used for radiocarbon dating, stable-isotope analysis and other forms of biochemical research.
La Brea is an exceptional Late Quaternary fossil deposit created by petroleum seepage over approximately the past 60,000 years. Its geoheritage profile notes that the site preserves millions of fossils representing hundreds of species.
The preservative, however, is also a contaminant. Petroleum contains ancient carbon that can distort radiocarbon dates. Researchers must therefore remove the asphalt carefully and isolate original organic material from the fossil.
The substance that protected the bone for tens of thousands of years must be persuaded to leave before the bone will surrender its age.
La Brea likes to keep its secrets sticky.
DATING EXTINCTION
Specialized methods for removing petroleum contamination have allowed researchers to obtain increasingly reliable radiocarbon dates from La Brea specimens.
In a major study of Ice Age extinction, scientists produced approximately 170 new dates for coyotes, horses, camels, bison, sabre-toothed cats, giant ground sloths, American lions and dire wolves. These dates helped establish when each species disappeared from Southern California.
The results suggest that the regional extinction did not occur in one sudden event. Large mammals vanished as the climate warmed, drought intensified, vegetation changed and fire activity increased. Human populations were also becoming established in the region, adding another ecological influence.
These pressures interacted. A warming climate altered habitats. Drought dried vegetation. Fire transformed plant communities. Large herbivores lost forage, while predators lost prey. Species able to change their diets or behaviour had an advantage over those dependent on a narrower range of conditions.
The Natural History Museums of Los Angeles County describes La Brea as an exceptional record because some species are represented by hundreds or thousands of individuals. This makes it possible to study not simply their existence, but their decline and disappearance through time.
The Tar Pits preserve extinct animals, but more importantly, they preserve the approach of extinction.
GIANT GROUND SLOTHS AND OTHER UNEXPECTED RESIDENTS
Among the more impressive herbivores at La Brea was Harlan’s ground sloth, Paramylodon harlani. Unlike modern tree sloths, it lived on the ground and possessed a heavily built body, powerful limbs and long claws. Small bony plates called osteoderms were embedded within its skin, providing an additional layer of protection.
It may have used its claws to pull down vegetation, dig for roots or defend itself from predators. When standing partly upright and supported by its tail, it could reach vegetation well above the ground.
Modern sloths give the impression that they would apologize for occupying your chair. Giant ground sloths look as though they might take the chair, the dining table and the adjacent shrubbery.
The deposits also preserve American lions, short-faced bears, pronghorn, peccaries and native horses, alongside reptiles, amphibians and an extraordinary diversity of birds. Asphalt is particularly effective at preserving delicate hollow bird bones, which are easily destroyed at other sites. As a result, La Brea holds one of the world’s largest fossil bird collections.
The birds are not merely background characters. Eagles, vultures, owls, ravens, waterbirds and songbirds occupied different parts of the ecosystem. Their remains help reconstruct habitats and food webs, while changes in bird communities can reflect broader environmental change.
ASPHALT AS A CULTURAL RESOURCE
The La Brea landscape has a human history as well as a palaeontological one. Indigenous peoples knew and used natural asphalt long before scientific excavation or commercial extraction began.
Tongva and Chumash peoples used asphalt to waterproof baskets and canoes, improve tools and create decorative objects. The material was also traded across the region. Educational material from La Brea Tar Pits recognizes this long history of Indigenous knowledge and use.
The asphalt was therefore not simply a dangerous geological substance. In knowledgeable hands, it was a valuable technology.
Commercial mining and extraction followed much later. Asphalt from Rancho La Brea was used for roofing and road construction before the area became protected for its fossils.
The site cannot be understood only as a trap for Ice Age animals. It is a cultural landscape where people observed, understood and worked with a distinctive natural resource for thousands of years.
A COLLECTION OF MILLIONS
Scientific excavation at La Brea began in earnest in 1913, although fossil bones had been encountered earlier. More than 100 excavations have since been conducted.
At the collection’s last comprehensive census in 1992, it already contained more than 3.5 million specimens. That number includes everything from large mammal bones to insects, seeds and tiny vertebrate remains. The La Brea collections include more than 60 mammal species, along with birds, reptiles, amphibians, fishes, molluscs, arthropods and plants.
The site remains scientifically active. Asphalt continues to seep, methane continues to bubble and fossil-bearing deposits continue to be excavated. La Brea is not a completed quarry whose discoveries are safely finished and catalogued. It is an active research site in the middle of a major city.
Beneath the lawns, streets and buildings, the Ice Age is still present.
A FOSSIL RECORD WITH A TRAP BUILT INTO IT
La Brea offers a particularly useful lesson in how fossil deposits must be interpreted.
The asphalt did not collect organisms fairly. Large animals were more likely to become immobilized than very small ones. Carnivores and scavengers were disproportionately drawn to trapped herbivores. Birds, insects and plants entered the deposits through different pathways. Individual seeps may also have accumulated remains over hundreds or thousands of years rather than during a single event.
We cannot simply count the fossils and assume the resulting proportions mirror the living community. More dire wolf bones do not prove that dire wolves vastly outnumbered bison across the landscape.
They may demonstrate that dire wolves were social, attracted to distressed prey and willing to step onto suspicious ground when meat was involved.
Understanding how remains accumulated is the work of taphonomy—the study of everything that happens between an organism’s death and its discovery as a fossil.
La Brea is both a window and a filter. It reveals the Ice Age, but it reveals it through asphalt.
THE STICKY ARCHIVE OF LOS ANGELES
There is something wonderfully improbable about La Brea. A city famous for reinvention sits above an archive of extinction. Traffic moves along Wilshire Boulevard while methane rises from petroleum formed by ancient marine organisms.
People walk through Hancock Park above the remains of mammoths, dire wolves and sabre-toothed cats. The past is not somewhere else. It is directly beneath the picnic blanket. Oh, how I would love to dig a little but they frown on that sort of thing in parks. Shame. Yes, we can see wonderful examples in the museum, but it is sheer pleasure to excavate yourself.
The Tar Pits preserve death in overwhelming abundance, but their scientific value lies in what they reveal about life. Their fossils tell us what animals ate, how they were injured, which plants grew around them and how ecosystems responded as the climate changed. Tiny seeds document shifting vegetation. Tooth enamel preserves chemical evidence of diet. Bones record growth, disease and survival.
Even the strange abundance of carnivores tells a story. One trapped herbivore could attract several predators. One tempting meal could produce fossils studied tens of thousands of years later.
The asphalt waited. The animals approached, encouraged by hunger and betrayed by optimism.
And the Earth kept every receipt.
Image Credit: Asset id: 2278428163. Prehistoric bones and the skull of saber-tooth cat, Smilodon fatalis, in a block of resin at the La Brea Tar Pits, Los Angeles, California
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