Long before highways cut across the Ozarks and rice fields spread across the Delta, the ground beneath Arkansas was part of a vast ocean floor. At different moments in deep time, that seafloor hosted everything from early shark relatives in the Carboniferous to the predators that left behind a 90-million-year record of teeth and bones. Today, that layered history is turning a landlocked state into “Sharkansas,” a place where eroding hillsides and roadcuts quietly expose one of the richest shark fossil stories in North America.
What makes this story remarkable is not just that sharks once swam where cattle now graze, but that some of their remains are preserved in three dimensions, with delicate gill structures and cartilage intact. That kind of anatomical fidelity is rare for sharks, whose skeletons are mostly cartilage, and it is forcing scientists to rethink how and where key steps in shark evolution unfolded.
From inland sea to “Sharkansas”
The nickname “Sharkansas” grew out of a simple, startling fact: the rocks under modern Arkansas record an ancient seafloor that, about 90-million-year ago, was crowded with sharks and their relatives. As that Cretaceous seabed hardened into limestone and shale, it locked away teeth and skeletal fragments that now spill out of creek banks and quarries, revealing just how thoroughly this inland sea was patrolled by predators. Those scattered finds, multiplied across the state, turned a quirky local moniker into a shorthand for a serious paleontological trove.
That Cretaceous story is only one layer in a much deeper stack. Beneath younger marine sediments lie older formations that captured earlier oceans and earlier shark lineages, so the same landscape that yields 90-million-year teeth also produces fossils from far more ancient intervals. It is this vertical time capsule, rather than a single moment in geologic history, that justifies treating Arkansas as a long running shark habitat rather than a brief anomaly, a point underscored by the density of fossils tied to those changing seas.
Carboniferous time capsules in the Fayetteville Shale
If the 90-million-year teeth explain the nickname, the real scientific fireworks are happening in rocks that are far older. The Fayetteville Shale, which underlies parts of northern and western Arkansas, dates to the Late Mississippian, in the early Carboniferous period, roughly 323 million years ago. In that interval, this part of the continent sat under a quieter, deeper marine setting, where fine muds settled over dead animals and quickly sealed them off from scavengers and oxygen.
Those conditions turned the Fayetteville Shale into a three dimensional archive of early shark anatomy, preserving cartilage, skull elements and even gill structures that almost never survive. Researchers who have worked this unit describe it as a shark fossil hotspot, not because it is packed with giant jaws, but because it captures the fragile parts that show how those jaws were built.
Ozarcus and the architecture of shark jaws
One of the most influential specimens from this Carboniferous seafloor is Ozarcus mapesae, a small shark relative whose skull was entombed in the Fayetteville Shale. When paleontologists prepared the fossil, they found that the head was preserved in three dimensions, with the entire gill skeleton still in place. That level of detail allowed them to trace how the gill arches connect to the jaws, something that is usually reconstructed from flattened impressions or from distant living analogues.
The researchers involved in the work emphasized that they “actually got the preservation of all the gill structure skeleton,” a rare stroke of luck that turned Ozarcus into a benchmark for studying early jaw evolution. The specimen, collected by Ohio Uni collaborators and later analyzed with modern imaging, showed that some features of shark gill arches are closer to bony fishes than previously thought, complicating simple stories about how jaws separated from gill supports. Coverage of the Ozarcus work highlighted how a single Arkansas fossil could reshape diagrams in textbooks worldwide.
Cosmoselachus and the surprise of shark gill covers
Ozarcus is no longer alone. Earlier this year, a team led by California State Polytechnic University researchers described Cosmoselachus mehlingi, another shark-like animal from the Fayetteville Shale. Like Ozarcus, Cosmoselachus is preserved in three dimensions, but it carries an anatomical twist: long pieces of cartilage that form a kind of gill cover. In living fishes, full gill covers are associated with bony groups like teleosts, while modern sharks have exposed gill slits, so finding a partial cover in a shark relative hints at a more experimental phase in early jawed vertebrates.
One researcher noted that Cosmoselachus has “mostly shark-like features, but with long pieces of cartilage that form a gill cover, which is only seen in ratfish,” linking it to a small group of modern chimaeras that bridge sharks and bony fishes. The same comments stressed that the Fayetteville Shale “preserves far more of the skeleton than we usually see,” crediting the unit’s fine sediments and low oxygen for the exceptional fidelity. Reports on Cosmoselachus underline how this single formation is yielding not just more fossils, but stranger and more informative ones.
The formal description of Cosmoselachus mehlingi, based on material from Arkansas and neighboring regions, reinforces that point. The team from California State Polytechnic University and other institutions emphasized that the same beds that hold these shark-like skeletons also contain exquisitely preserved invertebrate and plant fossils, a sign that the entire ecosystem was captured in a low energy, low oxygen setting. That broader context, detailed in the technical account of Cosmoselachus mehlingi, suggests that the same environmental factors that protected shark cartilage also froze entire food webs in place.
Why Arkansas keeps punching above its weight
It would be easy to treat these finds as lucky accidents, but the pattern points to something more systematic. Arkansas sits at a geological crossroads, where shallow Cretaceous seas, deeper Carboniferous basins and later uplift all intersect, so roadcuts and riverbanks slice through multiple marine layers at once. That makes it unusually likely that a farmer, a road crew or a weekend fossil hunter will stumble across a new specimen, especially in the northwestern part of the state where the Fayetteville Shale comes close to the surface.
Professional paleontologists have started to lean into that advantage, describing Arkansas as a place that “should be renamed Sharkansas” because of the sheer quality of its 3D shark fossils. One expert singled out a particular specimen as “so spectacular, even though it does not look like much at first glance,” a reminder that a nondescript gray rock can hide a fully articulated skull. Local coverage of these 3D shark fossils has, in turn, encouraged more residents to look twice at the stones in their own backyards.
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*This article was researched with the help of AI, with human editors creating the final content.
