Bear Gulch Limestone

Fossil Sites
 

Bear Gulch Limestone Fossil Lagerstätte


Geologic Time: Mississippian epoch of the Carboniferous, some 318 million years ago


Heath Shale Formation

 

Bear Gulch Limestone - Heath Shale Formation

The Bear Gulch Limestone in Montana is fossiliferous strata dating to the Mississippian epoch of the Carboniferous period, at some 318 million years ago. The site meets the stringent criteria for a Lagerstatte, with a diverse Mississippian biota of vertebrate and invertebrate fossils. The site is most famous for its diverse fishes that includes members of Orders Chondrichthyes (cartilaginous fishes), Actinopterygii (ray-fin fishes) and Sarcopterygii (lobe-fined fishes).

Sediment studies suggest that fossil formation occurred in mudflats and lagoons having fresh to brackish waters. The fossils comprise diverse fishes and less abundant invertebrates, sometimes preserved in exquisite detail consistent with inhibited decay in a silty and oxygen-starved bottom. The limestone is some 30 meters thick and covers about 25 square miles, and is posited to have been deposited during periodic episodes of heavy siltation that buried deceased members of the diverse ecosystem.

Bear Gulch Fossils

Male Echinochimaera meltoni Fish Fossil
Female Echinochimaera meltoni Fish Fossi
 
Discoserra pectinodon
Lepidasterella montanensis Starfish Fossil