Allenypterus montanus

Taxa: Allenypterus montanus

Geology: Heath formation-Bear Gulch 

Age: Mississippian-Carboniferous

Locality: Fergus County, Montana

 Allenypterus montanus

Allenypterus montanus was a small, unusual coelacanth from the Late Carboniferous of what is now Montana, living about 318–324 million years ago in tropical bay or estuarine waters. It had a distinctive deep, tear-drop or tadpole-like body, with a strongly elongated ribbon-like upper tail region and reduced fins, giving it a slow-swimming, maneuverable profile rather than the classic robust coelacanth look. Fossils suggest it reached only about 15 cm long, and preserved gut contents indicate it likely fed on small soft-bodied prey while moving through calm waters

 Bear Gulch Limestone

The Bear Gulch Limestone is a Late Mississippian limestone lens in central Montana, about 324 million years old, famous as a **lagerstätte** because it preserves marine life in exceptional detail. It formed in a shallow tropical bay in the Central Montana Trough and consists of fine-grained, laminated carbonate sediments deposited in short pulses, likely driven by seasonal storms and density flows that rapidly buried organisms in low-oxygen mud. As a result, it preserves a diverse Carboniferous ecosystem with fishes, invertebrates, algae, and even soft-tissue details such as gut contents and delicate body outlines, making it one of the most important fossil sites for studying Paleozoic marine life.