Scienmag reports on a new discovery in one of the world’s most famous (and most urban) fossil sites — an Ice Age toad species found in the La Brea tar pits:
Named Spea labreae, the extinct amphibian was identified in the long-studied collections of the La Brea Tar Pits, where its small bones had remained largely overlooked since they were excavated in the 1950s. The discovery adds a rare amphibian to the North American Pleistocene fossil record and offers scientists a new window into the environmental conditions that shaped Los Angeles at the end of the last Ice Age.
The species is described in the Journal of Vertebrate Paleontology by Dr. Alberto Cruz, a paleoecologist and paleogeographer who reviewed the Tar Pits’ understudied reptiles and amphibians while working as a postdoctoral fellow at La Brea Tar Pits. Cruz did not initially suspect that he was looking at an unknown animal. The unusual features of one specimen appeared so distinctive that he first considered whether the toad had suffered an injury or disease during its lifetime. Only after comparing the fossil material repeatedly with modern spadefoot toads did he conclude that the differences represented a previously unrecognized species.
“I’m really more of a paleoecologist, paleogeographer, not a taxonomist,” Cruz said, explaining that the discovery emerged unexpectedly during a broader review of the collection. The fossil material was originally collected decades ago, but detailed anatomical comparisons revealed characteristics that had escaped earlier investigations.
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The extinction of S. labreae therefore suggests that the habitats surrounding Rancho La Brea were reorganized as the Pleistocene ended and Southern California shifted toward the ecological conditions seen today.
The study also reports the first fossil record of the Mexican burrowing toad, Rhinophrynus, from the southwestern United States. Living members of this lineage are absent from modern Los Angeles, and their nearest populations occur nearly 2,500 kilometers away in southern Mexico. Finding evidence of the group in Ice Age Los Angeles indicates that its historical range once extended dramatically farther north. Together, the northward ancient presence of Rhinophrynus and the disappearance of S. labreae describe a complex ecological transition rather than a simple story of warming or cooling.