More than 300 million years ago, much of what is now Arkansas lay beneath a shallow sea.
Today, that ancient seafloor has made the region one of the most remarkable places in the world for shark fossils.
In northwestern Arkansas, rock layers known as the Fayetteville Shale have preserved dozens of rare shark skeletons from the distant past, earning the area the nickname “Sharkansas.”
Most shark fossils found around the world consist only of teeth. Unlike bones, shark skeletons are made mostly of cartilage, the same flexible material found in human noses and ears.
Cartilage usually decays quickly after an animal dies, so it rarely survives long enough to become fossilized.
That is why the Arkansas fossils are so extraordinary: they preserve entire three-dimensional shark skeletons, including delicate structures that almost never fossilize.
A new study published in the journal Geobios explains how this unusual preservation happened. Scientists discovered that the ancient seafloor where these sharks settled had extremely low oxygen levels and highly acidic conditions.
This harsh environment slowed the activity of bacteria that would normally break down soft tissues. As a result, the cartilage remained intact long enough to fossilize instead of disappearing.
At the same time, the acidic conditions dissolved bones and shells more easily than cartilage. This unusual chemistry explains why the area contains many shark fossils but very few remains of bony fish, even though those fish were common in ancient oceans. The conditions essentially favored sharks over other species in the fossil record.
Researchers from several institutions, including Cal Poly Humboldt and the American Museum of Natural History, studied the fossils and surrounding rock using advanced techniques such as X-ray scans and chemical analysis. By reconstructing the ancient environment, they were able to understand how these fossils formed in such remarkable detail.
The Fayetteville Shale has become one of the most important sites for studying early shark evolution. Some of the species discovered there, including Ozarcus mapesae and others, have helped scientists learn how modern fish evolved. Because the fossils are preserved in three dimensions rather than flattened, researchers can examine features like the skull, inner ear, and brain cavity — parts of the anatomy that are usually lost in other fossil sites.
Scientists believe that understanding the conditions that created “Sharkansas” could help them find other locations around the world where cartilage fossils might be preserved. Such discoveries would offer new insights into the early history of sharks and their relatives.
Even today, researchers continue to uncover new specimens from museum collections gathered in the region, showing that this ancient seafloor still has more secrets to reveal. What was once a quiet seabed has become a window into a distant era, helping scientists piece together the story of life in Earth’s ancient oceans.
