Bear Gulch Limestone

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
Caridosuctor populosum Coelacanth Class Sarcopterygii Family Rhabdodermatidae	Rare Harpagofututor volsellorhinus Shark Fossil Class Chondrichthyes Family Chondrenchelyidae	Male Echinochimaera meltoni Fish Fossil Class Chondrichthyes Family Echinochimaeridae	Female Echinochimaera meltoni Fish Fossil Class Chondrichthyes Family Echinochimaeridae
Aenigmacaris cornigerum Shrimp Fossil Class Malacostraca Order Cardoida Family Aenigmacaridae	Discoserra pectinodon Fish Fossil Class Actinoptergyii Family Guildayichthyidae	Lepidasterella montanensis Starfish Fossil Subphylum Asterozoa Class Stelleroidea Family Heliathasteridae