(Photo courtesy of NHMLAC)

Just after a heavy rain, the skies clear over a vast green field. A wild horse emerges from the tree line, passing a giant sloth grazing in the grass. The ground begins to shake. A herd of mammoths marches across the basin. Concealed in the nearby brush, a saber-toothed cat’s eyes dart from creature to creature – carefully selecting its next meal. At its feet, a toad hops into a murky puddle.

Welcome to Ice Age Los Angeles.

The period of Earth’s history from approximately 2.6 million to 11,000 years ago may seem unimaginably distant, but one L.A. institution continues to shape our understanding of the Pleistocene Epoch, or the most recent Ice Age, by digging deep into the past – literally.

For decades, the La Brea Tar Pits – an active fossil site, research institute and museum in the heart of Los Angeles – has brought the Ice Age to life through interactive fossil displays, educational tours and groundbreaking discoveries.

Tens of thousands of years ago, some of those horses, sloths, mammoths and saber-toothed cats became trapped in the sticky natural asphalt deposits in the middle of the L.A. basin. As they sank lower into the pits and decayed over time, asphalt seeped into the tiny pores within their bones, naturally preserving their skeletal remains for future generations of humans to discover.

By the early 1900s, excavations were well underway and scientists had begun researching the remarkable discoveries. A museum opened on the site in 1977, putting the fossils on public display for the first time. Today, the La Brea Tar Pits is home to millions (yes, millions) of these specimens, either prominently displayed – like the towering Columbian Mammoth bones in the George C. Page Museum – or carefully labeled and stored in seemingly endless rows of filing cabinets resembling the “Raiders of the Lost Ark” warehouse. Many Angelenos have fond memories of encountering these wild beasts on a field trip to the Tar Pits as schoolchildren, but few are aware of just how vital this site is to our understanding of the planet, both past and present.

“Most people who live in L.A. don’t know that they have one of the most important fossil sites in the world in the middle of their city,” said Dr. Emily Lindsey, curator and excavation site director of the Samuel Oschin Center for Global Ice Age Research at the La Brea Tar Pits.

Lindsey’s research examines what fossils can reveal about the climate and ecosystems of the Pleistocene Epoch, including why so many species went extinct. By studying how animals responded to periods of dramatic environmental change in the distant past, researchers can produce data that may help scientists anticipate how species will respond to climate change today.

“If we can understand when things were living here and when their range shifted and how that lines up with climate dynamics, that can actually be really informative data for people like land managers, policymakers and conservation scientists who are trying to predict how species are going to be impacted by the very significant climate change, anthropogenic climate change, that’s happening today,” she said.

Earlier this year, Lindsey and her colleague Dr. J. Alberto Cruz, a research associate at the La Brea Tar Pits and researcher for Mexico’s SECIHTI-Centro de Investigacion Paleontologica Quinametzin, Instituto Nacional de Antropología y Historia, published a groundbreaking discovery in the Journal of Vertebrate Paleontology. The study revealed something seemingly small that had been hiding in the Tar Pits collection for decades, yet had much larger implications for climate science.

Cruz, the study’s lead author, was reviewing the research center’s assortment of tiny reptile and amphibian bones first excavated in the 1920s, when he noticed one specimen that stood out – a spadefoot toad with an unusual shape. At first, Cruz thought it may have been sick or injured.

“I’m really more of a paleoecologist, paleogeographer, not a taxonomist,” said Cruz, explaining that his research usually focuses on studying the interaction between ancient creatures and their environments, rather than finding and naming new species. “I reviewed and reviewed a lot of specimens until I was convinced. I thought, ‘Oh my gosh, this is a new species.’”

Lindsey described the painstaking effort to rule out any other possibility, including but not limited to comparing it to the existing species in the Tar Pits’ own collection.

“He looked through all of the modern amphibian corresponding bones in the Natural History Museum here in L.A., and nothing matched,” Lindsey said. “He went up to the University of California, Berkeley, the Museum of Vertebrate Zoology. Up there is a massive collection, especially from California. He looked through all of that. It didn’t match anything, and so that’s when he realized that this was a new species.”

A tiny fossil revealed a new species of toad at the La Brea Tar Pits. (Photo courtesy of NHMLAC)

The now-extinct toad, Spea labreae, is the first new species named at the Tar Pits since a then-unknown bird species was unearthed in the 1990s, Lindsey said.

“This is a toad that was hopping around here in L.A. during the Ice Age, and it’s just completely gone from the planet today,” Lindsey said. “Amphibian bones are so tiny and fragile that they rarely preserve. They’re largely overlooked in fossil deposits. So there’s probably more that we just don’t know about yet.”

Lindsey explained that it’s incredibly difficult to determine when exactly this toad was likely hopping around. The fragility of the toad’s tiny bones makes radiocarbon dating practically impossible without destroying the holotype, or the specimen used to formally define the new species.

However, the newly discovered toad can still reveal remarkable insights into the end of the Pleistocene, a period typically associated with the extinction of megafauna – mammoths, giant ground sloths, mastodons and other enormous creatures. Beginning around 13,000 years ago, Southern California experienced a period of significant warming and drying, followed by centuries of intense wildfires and dramatic ecological upheaval. The changes coincided with the disappearance of the Tar Pits’ large animals, though scientists continue to study the roles that humans may have played in their extinction. Discoveries like Spea labreae help researchers understand how much smaller creatures may also have been impacted by the dramatically shifting landscape.

“The most significant thing that this fossil tells us is that there were small things that were impacted by the changes that were happening at the end of the Ice Age too,” Lindsey said. “It was a very size-selective extinction. Most of what we know that went extinct are the big mammals and, to a lesser extent, the big birds. But this is only the second extinct Ice Age amphibian that’s ever been found in North America.”

Lindsey said the discovery is particularly revealing given the amphibian’s unique adaptations. Spadefoot toads get their name from sharp hind feet that allow them to burrow into the soil before emerging in the right climate conditions.

“They have a pretty good talent for surviving times of hardship,” she said. “It looks like the habitat was so dramatically transformed, and also just experiencing this very high level of disturbance for so long that even a toad that’s maybe used to weathering seasonal variations in climate and hydrologic conditions just couldn’t make it through that multi-century period of environmental upheaval.”

The study also identified the first record of the Mexican burrowing toad at La Brea. Unlike Spea labreae, the species did not go extinct – but it no longer lives anywhere near Los Angeles. Today, the Mexican burrowing toad, or Rhinophrynus, is found thousands of miles away in southern Mexico, suggesting this species may have responded to a changing climate by dramatically shifting its range.

“There’s a lot of significant biogeographic shifts that are turning up as we’re going through our record, where we’re finding records of species that didn’t go extinct, but don’t live here in L.A. or maybe even in California or in this case even in the United States today,” Lindsey said. “Understanding that is really important because different species are going to respond differently to climate change, and these are probably largely climate-mediated shifts.”

The recent discovery of Spea labreae demonstrates just one of the millions of possibilities hiding within the La Brea Tar Pits. When asked if the collection of fossils may be home to more undiscovered animal species, Lindsey replied with confidence.

“I’d bet money on it,” she said.

The discovery comes as the La Brea Tar Pits campus undergoes the most significant transformation since its inception, an extensive $236 million modernization project ahead of the 2028 Olympic Games. The museum will remain closed for approximately two years, while each fossil, from mammoth tusks to amphibian vertebrae, is carefully packed up and transferred to secure off-site facilities where research will continue.

Lindsey emphasized that researchers will also keep digging at the Tar Pits while the renovation is underway, and visitors to the surrounding park can still catch a glimpse of scientists unearthing bones that reveal as much about the distant past as they do about our present day. The reimagined museum, Lindsey said, will further emphasize the modern-day implications of the discoveries being made at the Tar Pits, just like the spadefoot toad.

“Many people don’t even know that we’re actually a real scientific site, I think partly because people associate L.A. with all these imagined experiences – we have Hollywood, we have Disneyland, we have Universal Studios, we have tons of art museums,” Lindsey said. “La Brea is such a bizarre site … so people don’t understand that this is actually an incredibly important scientific resource. It’s probably one of the top five most important fossil sites of any age, anywhere on Earth, and it just happens to be in the middle of our city.”