Fossil of Extinct Leatherback Reveals Clues About Their Evolutionary Past

by · January 11, 2026

Leatherback sea turtles (Dermochelys coriacea) have seven dorsal ridges on their upper shells (carapaces) as seen in this nesting female. But millions of years ago, a ridgeless leatherback existed. Photo by Florida’s FWC.

Paleontologists have identified a ~ 32 million-year-old fossil found in Alabama in 2023 as a new extinct ridgeless leatherback species. The specimen was named Ueloca colemanorum and is one of the most complete leatherback fossils ever found.

Unlike hard-shelled sea turtles, leatherback carapaces are composed of irregularly shaped small bones (ossicles) held together by connective tissue which allows the carapace to flex during their deep dives. When a leatherback dies, the connective tissue decays and usually the ossicles separate and fall away. So, an intact fossilized leatherback shell is a rarity. In fact, less than 20 of them have been discovered worldwide.

What Did the Ridgeless Leatherback Look Like?

See an artist’s depiction of Ueloca colemanorum in The State of the World’s Sea Turtles (SWOT) article “Researchers Discover a New Species of Extinct Leatherback Sea Turtle”. The article includes a photo of the fossil, a graphic depiction of the carapace’s ossicles, and the updated leatherback family evolutionary tree.

Why Was Ueloca colemanorum Categorized as a New Species?

Paleontologist Dr. Andrew Gentry is the lead author of the research paper on Ueloca colemanorum and the Senior Education and Research Manager of the Learning Campus at Gulf State Park. He and a team of scientists first determined that the fossil was a leatherback sea turtle. Then, they compared its traits to those of all known extinct and living leatherbacks. In the October 2025 SWOT article, Dr. Gentry said that the new fossil had “a combination of features not found in any previously known species of leatherback sea turtle.” So, they named the new group of ridgeless leatherbacks Uelocini.

When Did Ueloca colemanorum Live?

This ridgeless leatherback lived during the first part of the Oligocene epoch between 32 and 33 million years ago. Both ridged (the Dermochelyini) and ridgeless leatherbacks existed during this time. Fossils of both ridged and ridgeless leatherbacks from the Oligocene had ossicles that were smaller and lighter when compared to older, 40-million-year-old specimens. This means that over time, both types of leatherbacks evolved carapaces that were more flexible to withstand the extreme pressures of deep dives.

Why Did Ueloca colemanorum Become Extinct?

According to Dr. Gentry, they don’t know exactly what caused ridgeless leatherbacks to go extinct and additional research is required. But studies have shown that the dorsal ridges of present-day leatherbacks help reduce drag while they swim and help them ascend after deep dives. These “hydrodynamic benefits” save them energy and make their foraging more efficient. Per Dr. Gentry, these benefits may have given them enough of an advantage to help them survive until today.

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