Mississippian Bear Gulch Fossil Sponge and Bivalve Association

Arborispongia delicatula

Phylum Porrifera

Aviculopecten sp

Phylum Mollusca, Class Bivalviaa

Geological Time: Mississippian

Size (25.4mm=1 inch): Sponge fossil: 80 mm, Bivalve fossil 25 mm by 20 mm across, Matrix: 75 mm by 140 mm

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

Code: BGF487

Price: Sold


Bear Gulch Fossil Sponge and Bivalve AssociationDescription: 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 plaque shows an arborescent (tree-like) sponge known as Arborispongia in association with a bivalve known as Aviculopecten. Bivalves and brachiopods are often found associated with these sponges; while the shelled part would obviously gain an attachment base, it is not known what benefit, if any, gleaned by the sponge.

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