Los Angeles was once home to a strange and terrifying agglomeration of giant ice age animals, from iconic saber-tooth cats to massive mammoths. At the end of the last ice age, they all mysteriously disappeared. L.A.’s premier fossil site may hold clues to what happened to these animals in its gooey asphalt.
Los Angeles is built on more than just broken dreams of stardom and glittery entertainment. Below the City of Angels are massive, gooey deposits of asphalt (not tar!). This viscous, low-grade form of crude oil is the remnant of ancient microscopic sea creatures, crushed by time and pressure deep within the earth. In 1923, Los Angeles produced nearly a quarter of the world’s oil by tapping into these immense reservoirs. Today, this dark, syrupy substance paves parking lots and roads, but 50,000 years ago, it created a vice-like death trap in the heart of what is now Los Angeles. As a result, we have an oily time capsule that gives us an intimate look at the animals that once ruled ancient Los Angeles, as well as clues into the forces that may have sparked their extinction.
Evidence of asphalt’s penchant to trap animals has been apparent since the first fossil animal bones were discovered at Rancho La Brea in 1875. Located on a posh stretch of Wilshire Boulevard in a public park next to the Los Angeles County Museum of Art, the former oil refinery is now home to the La Brea Tar Pits, one of the premier fossil sites for ice age fossils on the planet. Gooey asphalt still seeps out of the ground here, sometimes in brand new areas. The world’s first complete saber-tooth cat skull was discovered here. Dozens of mammoths have been exhumed from the asphalt, their bones creating a jumbled puzzle dozens of feet into the ground. The treasure trove of fossils in this sticky ice age graveyard vividly brings to life ancient Los Angeles, which would be unrecognizable to Angelenos today.
Instead of thousands of miles of paved streets and palm trees, primeval L.A. would have resembled the untamed plains of the Serengeti, only with a larger and stranger cast of characters. Huge herds of Columbian mammoths, each one weighing as much as five of the cars stalled in L.A.’s rush hour traffic, thundered across the savannah with a horde of animals you would never find here today, like camels, wild horses, hulking bison and elephant-like mastodons. 12-foot tall bears, mega-lions and packs of dire wolves terrorized these giant herbivores as condors and giant teraton birds (whose name literally means “giant bird” in Greek) with 11-foot wingspans soared overhead. The most famous creature here was the stocky Smilodon fatalis, or saber-tooth cat, who’s terrifying fangs help earn its distinction of California state fossil. Perhaps the strangest creatures here were the giant ground sloths who lethargically moved from tree to tree, using their immense claws to grab the top branches. The Harlan’s ground sloth, the largest species found in the Tar Pits, weighed a ton and a half!
Ancient Angelenos at the Page Museum (from left to right): Smilodon fatalis, dire wolf skulls, Columbian mammoth, American lion, and Harlan ground sloth.
Piecing Together Ancient L.A. with Clues from the ‘Tar’
Although these animals were gigantic, commonly referred to as megafauna (‘large animals’), they were far from safe around Rancho La Brea. The underground asphalt has been seeping towards the surface for millions of years, occasionally breaking through and creating a glistening puddle of molasses-like asphalt. This oil was often hidden by rainwater or fallen leaves, creating the perfect megafauna trap. Many of the immense animals roaming ancient Los Angeles would take a wrong step and become fatally ensnared in the bubbling asphalt. The more their giant bodies struggled, the more trapped they became, eventually starving as they sank into the oily depths of the earth. The fossil remains of predators are much more prevalent here as a dire wolf or saber-tooth cat seemed to crave a bite of a trapped bison leg or a hairy ground sloth rump stuck in tar. Over 4,000 dire wolves and counting have been pulled from this ‘predator death trap.’
Today, this ice age cemetery has produced 3.5 million plant and animal fossils from a hundred different individual tar pits that help paleontologists like Dr. Emily Lindsey and Dr. Regan Dunn, both associate curators at the La Brea Tar Pits, reconstruct L.A.’s ancient past. They work at the Page Museum, an onsite museum where the fossils removed from the tar pits are studied, stored and eventually exhibited to the public in all of their stained-black glory.
Although discoveries of large animals like mammoths and ground sloths captivate the public and stir up images of Los Angeles’ wild past, much smaller and seemingly mundane fossils act as an incredibly detailed diary of ice age Los Angeles, providing intimate clues about past climates. Dr. Dunn researches Rancho La Brea’s incredibly well-preserved fossil plants to reconstruct how ancient Los Angeles looked. “The [fossil] plants tie everything together and provide the context within each of these animals are making their living here.” The types of plant fossils, whether a preserved leaf, piece of wood or even a pinecone, tells scientists like Dunn what plants existed in certain areas, recreating what the overall habitat looked like when mammoths roamed L.A. The fossil remnants of a 27,000 year old California sycamore trees, for example, confirms there were streams and rivers at Rancho La Brea since the trees today only grow along the banks of permanent water sources.
Large fossilized tree trunks, mostly from long-living juniper trees, also help Dunn piece together the annual weather patterns tens of thousands of years ago. “Each year [junipers] make a ring and the size of that ring is dependent on how the growing conditions were that year.” A wetter year will produce bigger rings because the tree was able to stockpile more biomass thanks to the increased precipitation. By dating these tree fossils and then comparing the growth rates of each fossil, Dunn can learn a lot about “what the precipitation and temperature were like during the ice age [in Los Angeles].” The asphalt at La Brea even preserves pollen from the ice age, offering paleobotanists like Dunn one more tool to recreate ice age Los Angeles. From all these fossil clues, scientists at the Page Museum can determine how Los Angeles’ climate has changed over the past 50,000 years.
The Pleistocene garden outside the Page Museum displays several species of plants that once covered ice age Los Angeles. The garden occasionally gets a visit from a fellow remnant from that bygone era – a rabbit.
And how it has changed! When herds of Columbian mammoths roamed near the deadly tar pits some 40,000 years ago, Los Angeles was cooler and wet, creating a much lusher environment. Although this was during the last ice age, when ice sheets covered large swaths of the world including much of North America, Los Angeles was ice free. Instead of a frozen tundra, a variety of grasses and shrubs, with pockets of redwood and evergreen forests, flourished where languid ground sloths fed.
The Great Megafauna Extinction Debate
Similar to how the climate has changed in the last 40,000 years, so to have the inhabitants of Los Angeles. Many species, like coyotes, mountain lions and the recently extinct California grizzly bear, all survived along with smaller animals like rabbits and frogs into modern times. But gone are the mammoths, saber-tooth cats and ground sloths and most of the other large animals in La Brea’s asphalt pits. And scientists have not been able to pinpoint why these large animals all disappeared around the end of the Pleistocene epoch.
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“[The disappearance of the megafauna] has been one of the biggest debates in paleontology for the last sixty years.”
According to Dr. Lindsey, who has also examined fossils from contemporary asphalt pits in South America, this extinction was the most important extinction event since the dinosaurs were wiped out by an asteroid some 65 million years ago. “Very recently, everywhere except Africa [had] about 2/3 of its big animals go away, which had a huge impact [on global ecosystems].” In some places, almost all large animals went extinct. Australia and Southeast Asia, for example, lost 97 percent of their animals 110 pounds or bigger in a 10,000 year span from 50,000 to 40,000 years ago. The reason for this global loss of large animals “has been one of the biggest debates in both paleontology and archaeology for the last sixty years” according to Lindsey.
Australia’s megafauna extinction
Australia is known today for its collection of bizarre and dangerous animals, like koalas, kangaroos and a deadly collection of snakes. But if you were to travel back some 50,000 years, you would meet a host of monstrous beasts. There were wombats the size of rhinos, giant killer lizards some 25-feet long and tortoises the size of small cars. But the strangest, and possibly deadliest, was the marsupial lion Thylacoleo (left, at the Australian Museum in Sydney) that used its dagger-like claws and bolt cutter-like bite to dispose of the giant kangaroos of the day, often by dropping out of a tree. Like the disappearance of L.A.’s megafauna, the reason for the loss of these giants is not quite known but is probably some combination of Australia becoming more arid and the arrival of humans more than 50,000 years ago.
Lindsey explains there are two historical schools of thought on what caused the disappearance of the world’s megafauna. One school looks at how climate change at the end of the last ice age was causing the upheaval of many of the world’s ecosystems as the earth warmed. According to Lindsey, paleontologists can point to several examples, like the giant Irish elk in Europe, of species struggling when “their habitats are becoming climatically or ecologically intolerable.” The other school takes a more sweeping approach, looking at the spread of humans around the globe. In many cases, like in Australia, most of the large animals disappear within a few thousand years of the arrival of humans. The giant moa of New Zealand is another example of a megafauna that succumbed to human hunting. In the Americas, Lindsey says, the extinction was particularly swift. “When humans arrive in the Americas, within 5,000 years in North America, most of the large animals go away.”
Lindsey says she does not fall into either of these camps when it comes to the disappearance of the species found in the La Brea Tar Pits. She takes the point of view of a growing third group that looks at endangered megafauna today, like Africa’s rhinos and India’s tigers, and sees that the threats facing these species are extremely complex. “Large animals today are threatened by a variety of factors, like humans and climate change and habitat fragmentation and any number of intersecting processes,” Lindsey says. Today, she points out, most of Africa’s large mammals are protected on game reserves and in national parks. But when climate change makes these areas inhospitable, these animals are essentially trapped in these protected swaths of land because they cannot migrate out due to the human-modified landscape. In other words, climate change and human factors are essentially teaming up to cause megafaunal extinction today, which Lindsey believes supports the extinction theory of many species at La Brea 11,000 years ago. “Climate change is already impacting and fragmenting populations and then onto this landscape of weakened populations arrives this novel predator [humans] to naive fauna, creating a one-two punch.” The drawn out process of climate change causing extinction was often exacerbated by the arrival of spear-hurling humans that wiped out populations that were already struggling.
Art inspired by the Pits (clockwise): a comparison of the skulls of three cats found at La Brea; a re-imagination of the California state flag with the largest bear in the state’s history, the short-faced bear, which could run up to 30 miles an hour in short spurts!; Smilodon, the state fossil of California; and a few of the thousands of dire wolf remains buried in tar.
At the Tar Pits, Lindsey wants to use the sprawling collection of fossils to dig deeper into when specific species went extinct and compare that to the arrival of humans in Southern California. From work she has done in South America with fossils from this time period, Lindsey discovered that some megafaunal species, like ground sloths, not only survived the initial climate change, but also ended up living alongside humans for thousands of years.
Plant fossils and fossilized pollen are intricate clues to solving the climate change portion of the extinction puzzle as they preserve how the local environment has shifted since the end of the ice age. The animal skeletons removed from the tar pits can also offer clues to this shift of climates in California. Lindsey and other paleontologists at the Page Museum are examining fossil remains from four different pits originating in four different time periods from the end of the ice age. They will look to see whether the 5 most common species at the tar pits – dire wolves, saber-tooth cats, coyotes, Western horses and bison – physically transformed over tens of thousands of year in response to a warming climate. And the scientists here will seemingly never run out of fossil material to analyze.
In addition to the 3.5 million specimens already found, a collection of storage containers dot the landscape of Hancock Park, patiently waiting for paleontologists to dig into them. Many of these are from a huge cache of fossils that was unearthed when the Los Angeles County Museum of Art was excavating nearby land for their new parking garage in 2006. This discovery was among the largest this century, containing over 90 species in all, from tiny insects to a nearly complete skeleton of an 18,000 pound Columbian mammoth named Zed. This treasure trove of ice age fossils, dubbed Project 23 for the 23 gigantic crates housing all the bones and asphalt, could help define the roles that both climate change and humans played in the demise of Southern California’s megafauna over the last 50,000 years.
Above: Some of the 23 boxes that contain literal tons of fossil debris dug out from the nearby Los Angeles Museum of Contemporary Art parking lot.
Special thanks to Dr. Regan Dunn and Dr. Emily Lindsey for taking the time to discuss their research with me at the Page Museum.
All artwork and photography done by Jack Tamisiea.
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Sources:
https://www.wired.com/2012/02/la-brea-tar-pits/
https://tarpits.org/research-collections/tar-pits-collections/botany-collections
https://phys.org/news/2017-01-humans-climate-australian-megafauna.html
