New Ice Age spadefoot toad species identified from La Brea Tar Pits fossils

Paleontologists have named a new extinct species of spadefoot toad, Spea labreae, from fossils recovered at the La Brea Tar Pits in Los Angeles. The description, published in the Journal of Vertebrate Paleontology, is based on a single incomplete sacro-urostyle — the fused bone at the base of the spine that connects to the hips — collected decades ago but not closely studied until recently.

Lead author Alberto Cruz, a researcher affiliated with Mexico's Instituto Nacional de Antropología e Historia and the La Brea Tar Pits, identified the species while reviewing the site's understudied amphibian and reptile collections. Cruz compared the fossil to 80 modern spadefoot specimens held at the Natural History Museum of Los Angeles County and the Museum of Vertebrate Zoology at the University of California, Berkeley, confirming distinct morphological differences.

Spea labreae is only the second extinct Pleistocene amphibian ever documented in North America, following a tree frog from Florida. Amphibians rarely fossilize outside asphaltic deposits like the Tar Pits because their skeletons are fragile, making this find unusual. Cruz noted that the specimen was originally collected in the 1950s, illustrating how re-examination of existing collections can yield new species.

Because amphibians have limited mobility and high sensitivity to temperature and moisture, they serve as precise indicators of past local climate conditions. The presence of S. labreae, alongside the first fossil record of the Mexican burrowing toad (Rhinophrynus) in the southwestern United States, signals significant environmental shifts since the last ice age. Modern populations of the Mexican burrowing toad now live roughly 2,500 kilometers south in Mexico.

Emily Lindsey, curator and excavation site director at the Samuel Oschin Center for Global Ice Age Research at La Brea Tar Pits, said the discovery underscores that new findings continue to emerge after a century of excavation. Cruz and colleagues are now investigating other asphaltic sites, such as Talara in Peru, to further document microvertebrate responses to past climate change.

The study acknowledges that many more extinct amphibians and reptiles likely existed but left no fossil trace due to their delicate bones. Researchers caution that the single holotype specimen limits knowledge of the species' full anatomy and variation, and further finds are needed to clarify its ecology and evolutionary relationships.