Shark Seas of Sherman: Ancient Oyster Reef Project

When you take people down Post Oak Creek to “pan for shark teeth,” you’re not just running a fun treasure hunt. You’re sliding across the edge of a vanished ocean.

North Texas (including the Sherman area) sits on rocks laid down during the Late Cretaceous, when a warm, shallow sea covered large parts of the region. The creek is one of those rare places where modern erosion peels back the cover and exposes fossil-bearing layers from that ancient seafloor, especially units within the Eagle Ford Group and the Arcadia Park Formation. 

And the “Ancient Oyster Reef” piece is not just a catchy banner. Post Oak Creek is famous for dense oyster shell beds (reef-like shell accumulations) that show up as cemented, flaggy sandstone layers and shell hash. Collectors consistently note oyster-rich beds plus abundant shark teeth weathering out of those same layers. 

Our recent videos have helped shine a spotlight on Post Oak Creek, which has quickly become one of North Texas’ most talked-about fossil-hunting locations. As interest in the creek has grown, so has the conversation about how best to protect it for the future.

The City of Sherman is actively planning a new park along the Post Oak Creek corridor. Public reporting has described this effort as a way to improve safety, manage access, and conserve the creek’s unique natural and historical resources, with land acquisitions included as part of that long-term vision.

At the same time, there is growing state-level conservation interest in the area. The Texas Parks and Wildlife Department (TPWD) is developing new state parks across Texas, reflecting a broader commitment to protecting important natural landscapes. While Post Oak Creek is not yet officially designated as a state park, the increased attention highlights the creek’s value as a place worth preserving.

Together, these efforts point toward a shared goal: protecting Post Oak Creek so future generations can safely explore, learn from, and enjoy one of North Texas’ most remarkable windows into the ancient past.
 

Post Oak Creek isn’t just a fossil conveyor belt. It’s part of the city’s origin tale.

• Sherman was founded in 1846, then moved in 1848 to its current site specifically because the original location lacked reliable wood and water. In other words: water shaped where the city could live.
   
• The Handbook of Texas describes Postoak Creek rising northwest of Sherman and running southeast to Choctaw Creek, crossing prairie soils and vegetation typical of the region. That’s your modern ribbon of green cutting through Blackland Prairie and riparian habitat.
   
• Sherman grew into a major North Texas hub with rail connections and industry; the creek corridors and floodplains around town were part of the lived landscape long before “recreation access points” were a concept.
   

Sherman moved for water. And now, in that same water, we find teeth from a sea that vanished 90 million years ago.

In and around Sherman, Post Oak Creek cuts into Upper Cretaceous marine strata, especially the Eagle Ford Group, including the Arcadia Park Formation/Shale and associated sandier members in the north (notably the Bells Sandstone Member in Grayson County). These sandier layers are famous for producing shells and teeth because sandstones and shell beds weather differently than the surrounding shales, releasing durable fossils into the creek. 

A very practical field note from collectors/geologists in North Texas: the creek bed is often in the Arcadia Park unit while nearby banks may expose the overlying Austin Group, meaning the creek is naturally “mining” the fossil-rich contact zone.

Picture a shallow sea shelf:

• Patchy sand bodies and storm layers.
   
• Thick mats of oysters and shellfish building shell concentrations (reef-like communities).
   
• Predators cruising overhead, plus rays and fish along the bottom.
   

That’s why you get the signature combination: oyster hash everywhere and shark teeth everywhere. 

Sharks shed teeth like living confetti over their lifetimes. Teeth are also built from extremely durable, mineral-rich tissues (enamel-like cap plus dentine), so when the rest of the animal decays, the teeth persist and fossilize readily.

Then geology does a second trick: concentration. In energetic settings (storms, currents), lighter mud winnows away while heavier bits (phosphate teeth, dense bone, shell fragments) collect into lag deposits. Those laggy shell beds are exactly what your guests are sifting in the creek today.

In the Eagle Ford/Arcadia Park context, collectors routinely find a mix of crushers, slicers, scavengers, and needle-toothed fish-eaters. Here’s a solid, teachable field guide framing for Sherman/Post Oak Creek-type material:

Ptychodus

• Broad, ridged, almost “cobblestone” teeth designed for crushing shells.
   
• These are the teeth that make people say, “Wait… that’s a shark tooth?” because they don’t look like daggers.
   
• Ptychodus is widely associated with Late Cretaceous marine deposits like the Eagle Ford, and commonly reported by collectors at Post Oak Creek.
   

Narration idea: “These are the oyster-reef specialists. If the creek is an ancient buffet, Ptychodus brought the nutcracker.”

Commonly discussed Eagle Ford shark taxa include:

• Cretoxyrhina (large predatory lamniform sharks, often described as major apex predators of the time)
   
• Squalicorax (often interpreted as opportunistic/scavenging behavior in many contexts)
   
• Cretalamna and Cretodus (lamniform sharks represented by sharp teeth in Cretaceous marine deposits)
   

These genera are repeatedly listed/illustrated in Eagle Ford collecting resources and reports. 

You’ll also see narrower teeth often attributed to sand-tiger-type lamniforms (examples commonly discussed in Cretaceous marine assemblages include Scapanorhynchus), plus rays and other cartilaginous fish elements mixed into the same beds. 

Microfossil hunters at Post Oak Creek report ray material alongside shark teeth (for example, Ptychotrygon is a ray genus known from Cretaceous deposits and shows up in fossil databases tied to the Eagle Ford Group). 

Here’s a simple “three-act” structure you can deliver while paddling:

• Take only loose finds already in the gravel/sand (no digging banks, no prying bedrock).
   
• Leave big, unusual, or articulated material in place and report it (that’s where science value jumps).
   
• Pack out trash as part of the program identity (the creek as classroom, not quarry).
   
• Safety: foot protection, shuffle steps, watch for glass/metal in urban creek corridors, and be mindful of sudden weather upstream.