Orbiculoid Brachiopods with Preserved Natural Shell from Bear Gulch


Brachiopoda, Lingulida, Discinidae

Geological Time: Mississippian

Size: 12 mm – 26 mm across

Fossil Site: Heath Shale Formation, Bear Gulch Limestone, Fergus County, Montana

Orbiculoid Brachiopod FossilsDescription: The Bear Gulch Limestone is a deposit of some 70 square km in extent and 30 m in depth that has been a source of one of the most diverse assemblages of fossil fish with some 110 species having been described over the past 30 years. Most were new to science, and provided a unique view of the marine environment of Mississippian times. Fine preservation of both fish and invertebrates is a hallmark of these deposits, presumably due to an anoxic depositional environment. This is a group of inarticulate brachiopods known as orbiculoids. Notice the preserved original shell on some examples, as well as the growth rings. The depositional environment must have been nonacidic in order for original shell to be preserved as seen here.

click fossil pictures to enlarge

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