Phanerosteon phonax Paleozoic Paleoniscoid Fish Fossil

from Bear Gulch Heath Shale Formation

Phanerosteon phonax

Actinoptergyii, Paleonisciformes, Carbovelidae

Geological Time: Mississippian (~320 m.y.a.)

Size: Fish fossil: 105 mm long Matrix: 270 mm by 185 mm

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

Phanerosteon phonaxDescription: 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 very well-preserved example of a Paleoniscoid fish known as Phanerosteon. The paleoniscoids were the first ray-finned fish, a feature readily seen here. Phanerosteon was scaleless in the anterior, with scales present primarily on the caudal peduncle. Some 40 or more families appeared during the Carboniferous and Permian Periods.

Also see: Paleozoic Fish Fossils


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