A single fossilized rib uncovered in a Yazoo County creek bank has been identified as belonging to Zygorhiza, a large toothed whale from the late Eocene (about 38–34 million years ago). Zygorhiza measured roughly 15–18 feet and weighed around 5,000–7,000 pounds; its serrated, arrowhead-shaped rear teeth indicate it could tear large prey. The discovery reflects that central Mississippi was once part of the Jackson Sea, and scientists say rapid climate cooling and continental changes at the end of the Eocene likely contributed to the extinction of these whales.
Small Creekbank Find Reveals Fossil Rib of a Ferocious Eocene Whale in Mississippi
A single fossilized rib uncovered in a Yazoo County creek bank has been identified as belonging to Zygorhiza, a large toothed whale from the late Eocene (about 38–34 million years ago). Zygorhiza measured roughly 15–18 feet and weighed around 5,000–7,000 pounds; its serrated, arrowhead-shaped rear teeth indicate it could tear large prey. The discovery reflects that central Mississippi was once part of the Jackson Sea, and scientists say rapid climate cooling and continental changes at the end of the Eocene likely contributed to the extinction of these whales.
04:41 PM, 11/11/2025Science
Fossil rib of Eocene whale discovered in Yazoo County
What started as a small sliver of bone protruding from a creek bank turned into an unexpected paleontological discovery: a fossilized rib from a large, toothed whale that lived during the late Eocene Epoch and went extinct roughly 34 million years ago.
Discovery. Robbie Ellwanger, a fish and mussel biologist with the Mississippi Museum of Natural Science, was conducting fieldwork in late October when he noticed the fragment. "I was just walking along and saw it sticking out of the bank," Ellwanger said. He dug around the bone and uncovered an intact rib, though additional bones from the same animal were not found.
"It was cool. I haven't found a full rib like that before... It's always exciting when we find any kind of fossilized material." — Robbie Ellwanger
Identification. Museum paleontologist George Phillips quickly identified the rib as belonging to Zygorhiza, a member of the extinct basilosaurid (zeuglodont) whales. These animals lived between about 38 and 34 million years ago. Adult Zygorhiza reached roughly 15–18 feet in length and weighed an estimated 5,000–7,000 pounds.
Why a whale in central Mississippi? The find reflects ancient geography: during parts of the Cretaceous and into the Eocene, the Mississippi River Valley was inundated by an arm of the Gulf of Mexico. Phillips explained that the region known as the "Jackson Sea" once extended inland, placing the shoreline somewhere between present-day Clarksdale and Memphis when Zygorhiza lived there.
How they lived and hunted. Though smaller than some relatives, Zygorhiza were formidable predators. James Starnes, associate state geologist, noted that relatives such as Cynthiacetus maxwelli could reach about 30 feet and Basilosaurus around 70 feet. Zygorhiza were likely faster and more agile than these larger cousins. Their front teeth were peg-like for grasping, while posterior teeth were arrowhead-shaped with pronounced serrations—adaptations for slicing and tearing larger prey.
Starnes added, "These were not cute little dolphins out there. These were quite ferocious animals." If Zygorhiza hunted cooperatively like modern dolphins and orcas, encounters with packs would have been particularly dangerous for other marine animals.
Extinction. Zygorhiza and other basilosaurids persisted for millions of years but disappeared at the close of the Eocene. There is no single agreed cause for their extinction; however, global cooling and the emergence of polar ice sheets altered oceanic circulation and habitats. Continental drift and shifting coastlines likely also played major roles, and their disappearance appears abrupt in geological terms.
Context and source. The discovery highlights both the fossil potential of Yazoo County and the deep-time changes that transformed the Gulf coastline. The find was reported by the Mississippi Clarion Ledger and confirmed by museum scientists.