La Brea Tar Pits' Tiniest Fossils Provide a Key to Lost Worlds
If you're not looking carefully, you might miss the fossils entirely. About the size of a matchstick head, the asphalt-permeated vertebrae, seed pods and insect parts don't carry the same grand sense of drama as a mastodon femur or a sabercat tooth. And yet, despite the fact that Los Angeles' La Brea Tar Pits became famous for its outstanding collection of Ice Age megafauna, it's the tiniest fossils that are offering us the clearest view to what prehistoric SoCal was like during the time that dire wolves roamed the grasslands and giant sloths browsed among the trees. Called microfossils, the more miniscule remnants of the past are having the biggest influence on how we understand ancient L.A.
People have known about the tar pits for centuries. The Chumash and Tongva people utilized the natural asphalt oozing out of the ground to seal their boats and baskets, among other uses, and European colonizers would later use the tar on the roofs of their homes. Naturally, it was hard to ignore the chocolate brown bones found amongst the tar, but these were often interpreted as the remains of pronghorn, cattle or various wild animals that had become stuck and perished. It wasn't until 1901 that naturalists began to realize that many of the bones in the tar belonged to species that vanished long ago. And when paleontologists started to dig in, they uncovered the richest fossil treasure trove on the entire planet.
Beginning about 1913, early scientific excavations of La Brea turned up a startling number of Ice Age organisms. There were mammoths and mastodons, sabertoothed cats and dire wolves, giant sloths and enormous camels, their tar-stained bones jumbled together. At the time, paleontologists wanted the biggest and strangest creatures they could find. "Little care was given to preserving less-than-perfect bones," Lindsey says, and experts dug wantonly with picks and shovels in spots of "poor bone quality" as they searched for better fossils. The paleontologists of the time were thinking about specimens for a museum and charismatic animals to study, which meant that they often didn't take precise notes or collect anything smaller than a coyote from the pits.
The bones extricated from the pits began to form the beginnings of a huge fossil collection of what would be dubbed the George C. Page Museum in 1977, an on-site museum where excavation, preparation and display of La Brea's unique fossils could continue. Naturally, the museum proudly displayed some of the biggest and most impressive creatures of Pleistocene California — everything from the reconstructed skeletons inside to the bas relief depiction of Ice Age La Brea around the museum emphasized the great beasts of the tar pits. But even as those animals began to draw visitors, there was a change going on at La Brea.
La Brea is not a single pit, but many, each with its own name. In 1969, not long before the George C. Page Museum was opened, La Brea paleontologists started a new project in Pit 91. "We started taking precise measurements on all the fossils excavated," Lindsey says, building a database of how the fossils were situated within the pits. More than that, experts began to appreciate the wealth of fossil material at the small scale – from lizard jaws to snail shells. Uncovering these fossils required a more delicate approach. "We started using dental picks instead of trowels and shovels," Lindsey says, with every effort made to find all the fossils – not just the likes of Smilodon and Megatherium. If paleontologists were to understand the whole story of La Brea, they would have to think smaller.
"The thing about the big sexy animals is that they had really broad ecological tolerances and geographic ranges," says La Brea Assistant Curator Emily Lindsey. In one 2021 study, for example, paleontologists found that woolly mammoths could roam over 300 miles in a matter of months. The big and impressive animals were not exclusively tied to La Brea even as they ultimately became buried there. But small organisms are often much more closely associated with the local environment. "Particular species of plants, insects, lizards, songbirds and rodents can be much more ecologically sensitive," she adds, and therefore were more responsive to changes in climate and vegetation. The small species are like biological markers, indicators for details that we might entirely miss otherwise.
Even the tiniest fragments of prehistoric insects can tell us a great deal. In 2017, entomologist Anna Holden and colleagues published a study on beetle pieces found in La Brea. The fossils in the study were radiocarbon dated to get an estimate of their age, forming a nearly continuous sample from about 50,000 to 4,000 years ago. Because the beetle species in the sample are still alive and can be taken as environmental indicators of particular climates, the researchers were able to reconstruct La Brea's climate through time. Perhaps strangely for a time called the Ice Age, the researchers found, La Brea's ancient climate was very similar to the dry and warm climate of modern L.A. And that's hardly all, Lindsey notes. "We have tons of turtle remains at our site, and some of the deposits have rainbow trout and freshwater mollusks," she says. These creatures didn't just wander in from some other place, but indicate that there were slow-moving streams at La Brea that hosted some very familiar species.
In fact, it may be that the small or overlooked organisms of La Brea might be able to tell us something about the fate of those towering, sharp-toothed and ferocious animals that often draw visitors to the fossil site's museum. To this day, paleontologists debate why many of the Ice Age megafauna disappeared. "Despite 70 years of intense focus, the Pleistocene extinction event remains poorly understood," Lindsey says. Some experts propose that hunting by humans was the primary trigger for ecosystem collapse. Others think rapid changes to the global climate as the world went from cold and dry to warmer and wetter had something to do with it. Then again, both explanations might turn out to be correct in some circumstances — made all the more complicated by the fact that we don't understand why creatures like coyotes, black bears and gray wolves were able to survive while similar species perished.
The nature of the fossil record makes it difficult to draw out the big picture. Most Ice Age fossil sites around North America, and the world, contain a much smaller sample of the local species over timeframes that are difficult to compare. But the record at La Brea is nearly continuous over the course of more than 50,000 years, documenting how the environment shifted and how organisms responded. During some particularly harsh and dry years, for example, it seems that the sabertoothed cat Smilodon gnawed more bones than other times — hinting that there was less food and the normally flesh-focused cats had to make the most of every meal. "The La Brea tar pits is one of the best opportunities to really look at extinction dynamics because we have so many fossils," Lindsey says, a vast fossil library down to the tiniest fragments.
There are certainly more discoveries to come, not only through analysis but through excavations of the tar-soaked sediment. In 2006, the neighboring Los Angeles County Museum of Art started to build a new parking garage — and they quickly hit an impressive pocket of fossils. It would take decades to excavate everything in situ, so paleontologists packaged up massive chunks in wooden tree boxes to move behind La Brea and continue uncovering fossils at a more comfortable pace. Dubbed Project 23, the endeavor is still continuing 16 years later. Every dire wolf jaw, every songbird bone, every snail shell that's freed from the sticky layers of La Brea is another part of the story, an Ice Age epic that we are only just now beginning to envision.
