Prehistoric Whale

Zygorhiza kochii is Mississippi's official state fossil, designated in 1981. It was an archaeocete — one of the ancient lineage of primitive whales that still retained small hind limb vestiges inherited from their land-dwelling ancestors. During the Late Eocene, much of present-day Mississippi lay beneath a warm, shallow sea, and Zygorhiza was one of its top predators.

Zygorhiza kochii reached up to 20 feet in length and had a long, low skull with large triangular teeth serrated for gripping fish. Unlike modern whales, it had a flexible spine and tiny vestigial hind limbs — small bony remnants of the legs its ancestors used on land. Its body was elongated and likely moved with an eel-like undulation rather than the up-and-down motion of living whales.

Zygorhiza was smaller than its relative Basilosaurus but hunted the same warm Eocene waters. It ate fish, sharks, and possibly other marine mammals. The lineage died out at the end of the Eocene, about 34 million years ago, as ocean temperatures dropped and more advanced whale groups took over.

Zygorhiza kochii fossils have been known from Mississippi since the 19th century, when collectors working the exposed clay beds of eastern Mississippi recovered vertebrae and skull fragments. The species name kochii honors Albert Koch, a fossil collector who excavated archaeocete remains from the Gulf Coast region in the 1840s.

Mississippi designated Zygorhiza kochii as its official state fossil in 1981. The choice reflected the state's Eocene marine heritage — a period when the Gulf of Mexico extended far inland and Mississippi was the seafloor rather than dry land.

Most Zygorhiza kochii fossils in Mississippi come from the Yazoo Clay, a Late Eocene marine formation that outcrops across a band of eastern Mississippi counties including Clarke, Lauderdale, and Kemper. Road cuts, stream banks, and eroded hillsides in this region regularly expose whale vertebrae and teeth.

The Mississippi Museum of Natural Science in Jackson displays mounted skeletal material and is the best public site to see the state fossil. Additional specimens are held in university collections across the Gulf Coast region.