Reticycloceras Fossil Orthocone Nautiloid

Reticycloceras sp

Class Cephalopoda, Subclass Nautiloidea, Order Nautilida, Family Pseudorthoceratidae

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

Size: Fossil is 74 mm long

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

Description: 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 specimen is a an orthocone nautilod known as Reticycloceras. The orthocones derive their name from their essentially straight shell; some from the Ordovician and Silurian reached lengths of 3 meters. The dark spot on the one side is most likely remains of the ink sac.

Reticycloceras Mississippian Bear Gulch Fossil Orthocone Nautiloid

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