Oceanside construction project unearths 40-million-year-old prehistoric fossils

Paleontologists have discovered fossilized remains of a massive prehistoric mammal during a routine water infrastructure project in Oceanside, California. The fossils, estimated to be between 40 and 45 million years old, were found approximately 12 to 15 feet below the surface within the Santiago Formation, a sedimentary rock layer dating to the Eocene Epoch.

The discovery was made by principal paleontologist Joseph El Adli, who identified an unusual object protruding from an excavation wall. After a multi-day excavation of several tons of hardened mudstone and sandstone, the team recovered multiple limb bones, ribs, and fragments that appear to belong to a single large animal. The largest specimen is a femur measuring between 2.5 and 3 feet in length.

Experts believe the remains belong to one of two extinct mammal families: the Brontotheriidae, commonly known as ‘thunder beasts,’ or the Amynodontidae, often referred to as ‘swamp rhinos.’ While both were large herbivores, the brontothere is considered a more likely candidate due to its prevalence in the region at that time. The specimens have been transported to a laboratory in Carlsbad for further study and may eventually be transferred to a museum, such as the San Diego Natural History Museum.