Crustacea, Class Malacostraca, Subclass Hoplocarida, Order Palaeostomatopoda,
is 73 mm long
Heath Shale Formation, Bear Gulch Limestone, Fergus County, Montana
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.