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Large Eocene Mammal Fossils Found During Oceanside Construction

A tentative identification as either a brontothere or an amynodont could reshape understanding of Eocene mammals in coastal Southern California pending further study.

Overview

  • A consulting paleontologist discovered the first fossil fragment on Aug. 31, and crews paused a water‑infrastructure dig while a staged rescue excavation recovered limb bones, ribs, and other fragments.
  • Teams encased the bones in plaster during a multi‑day effort and removed very large elements from about 12 feet below the surface for transport to a laboratory in Carlsbad.
  • Based on limb proportions and the rock layer, scientists have narrowed the animal to two possibilities — a brontothere (a large, hump‑shouldered herbivore) or an amynodont (a semi‑aquatic rhino relative) — but a definitive ID requires skull or teeth.
  • The fossils come from Member C of the Santiago Formation, an Eocene unit known to preserve North American vertebrates, which helped narrow the likely age to roughly 40–45 million years ago.
  • Oceanside is withholding the exact site location for safety and preservation, officials say, and the material will undergo preparation and study in the lab before being transferred to a museum for public curation.