Rare Bear Gulch Fossil Mantis Shrimp Precursor

"Part and Counterpart"

Perimecturus rapax

Subphylum Crustacea, Class Malacostraca, Subclass Hoplocarida, Order Palaeostomatopoda, Family Perimecturidae

Geological Time: Mississippian

Size: Fossil is 73 mm long

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

Perimecturus rapaxDescription: 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 proto mantis known as Perimecturus rapax. The genus is also known from the older Visean deposits of Scotland (~340 million years ago). The modern Mantis Shrimps are rapacious carnivores (the source of the species name) that employ a slash and grab lifestyle. Presumably this taxon shared that same modus operandi. This is a part/counterpart example of a relatively rare taxon that composes~5% of arthropods from Bear Gulch.


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