Paleozoic Bear Gulch Coiled Cephalopod Fossil

with Preserved Jaws

Anthracoceras sp.

Class Cephalopoda, Order Goniatida, Family Anthracoceratidae

Geological Time: Mississippian (~320 million years ago)

Size: Fossil is 35 mm across; Matrix: 70 mm by 65 mm

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

Fossil Code: BGF154

Price: Sold

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 goniatitic ammonite of the genus Anthracoceras. The Ammonidea have a rich evolutionary history which began in the Upper Silurian/Lower Devonian. The order began an extensive radiation in the Triassic and Jurassic, and became most diverse during the Cretaceous, only to become extinct during the late Cretaceous extinction event which also saw the demise of the non-avian dinosaurs. The Goniatite forms became extinct during the Permian. Specimens from the Mississippian are not often seen, making this example most unusual. The most unusual feature is that the jaws are preserved within the shell of this fine specimen. See my other listing for a coprolite containing numerous jaws.

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