Scientists Discover New Ice Age Toad Species Hidden in La Brea Tar Pits

A previously unknown species of Ice Age spadefoot toad has been identified from fossils excavated at California’s famous La Brea Tar Pits, making it only the second extinct Ice Age amphibian ever discovered in North America.

The fossils, originally unearthed in 1929 and stored in museum collections for decades, were recognized as a new species during a recent review of the collection. Named Spea labreae, the toad was described Aug. 4 in the Journal of Vertebrate Paleontology.

The discovery adds a small but scientifically important animal to a fossil site best known for mammoths, saber-toothed cats and dire wolves. Researchers say amphibians are especially valuable because they are highly sensitive to changes in temperature and rainfall. That means fossils like Spea labreae can help scientists reconstruct what Southern California’s environment looked like during the last Ice Age and better understand how ecosystems responded to past climate change.

Tiny fossils reveal a new Ice Age species

The discovery began when lead author Dr. J. Alberto Cruz reviewed the La Brea Tar Pits’ largely unstudied amphibian and reptile collection. Among fossils collected nearly a century ago, he found two small bones, each about 1 centimeter long, belonging to the lower spine and hip region of a spadefoot toad.

After comparing the fossils with about 80 modern amphibian specimens housed at the Natural History Museum of Los Angeles County and the University of California, Berkeley, Cruz concluded they belonged to an entirely new species.

“I’m really more of a paleoecologist and paleogeographer, not a taxonomist,” Cruz said in a statement from the Natural History Museum of Los Angeles County. “I reviewed and reviewed a lot of specimens until I was convinced. I thought, ‘Oh my gosh, this is a new species.’ This material is originally from the 1950s, but when you study it again, you can find gold in these specimens.”

Study co-author Dr. Emily Lindsey, curator and excavation site director at the Samuel Oschin Center for Global Ice Age Research, said the finding highlights how much remains to be learned from existing museum collections.

“It’s a great example of how we’re still finding new things at La Brea Tar Pits, even after a century of ongoing excavation and research,” Lindsey said. “There’s definitely more to come.”

Why amphibians are important climate clues

Unlike large mammals that can roam over vast distances, frogs and toads usually stay close to water and rarely travel far from where they hatch. Because they are highly sensitive to temperature and moisture, scientists use their fossils to understand ancient local climates.

“If you change the environment, you change the vegetation; the climate is warmer or colder, it affects these animals directly,” Cruz said.

The study also identified the first fossil evidence that the Mexican burrowing toad (Rhinophrynus dorsalis) once lived in what is now the southwestern United States. Today, the species survives only in parts of Mexico, Central America and extreme southern Texas, with its closest known populations roughly 2,500 kilometers (1,550 miles) south of Los Angeles.

Researchers say the presence of that species suggests Southern California was once much wetter than it is today, supporting habitats that no longer exist in the region.

A rare window into the Ice Age

Amphibian fossils are uncommon because their small, fragile skeletons rarely survive long enough to fossilize. The sticky asphalt at La Brea Tar Pits preserved these delicate bones by protecting them from decay, scavengers, and weathering, making the site one of the few places where such discoveries are possible.

“Due to their fragile skeletons, amphibians like frogs, toads, and salamanders rarely make it into fossil records outside of asphaltic sites like the Tar Pits,” Cruz and Lindsey said in a joint statement. “The discovery of a new species is an extraordinary find at the Tar Pits.”

Outside experts say the discovery also highlights how overlooked small fossils can reshape scientists’ understanding of prehistoric ecosystems.

“The fossil record of frogs and toads goes back to 200 million years, and most of what we know is isolated and broken bones,” David Blackburn, associate director of research and collections at the Florida Museum of Natural History, told CNN. “It is surprising that relatively few frog fossils have been previously recovered from La Brea, and I’m confident more will turn up.”

Researchers believe continued study of La Brea’s collections could reveal additional overlooked species while providing new insights into how ancient amphibians responded to natural climate shifts, knowledge that could help scientists better understand how today’s amphibians may cope with ongoing human-driven climate change.