Juvenile Iniopterygian “Flying Shark” Fossil from Bear Gulch
Part and Counterpart

Inioppterygii indet.

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

Size (25.4 mm = 1 inch): Fish fossil: 22 mm long; Matrix: 250 mm by 175 mm and 185 mm by 145 mm pair

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

Inioppterygii Shark FossilDescription: 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 member of the little-known and poorly understood Iniopterygii. Most have yet to be described. They are collectively characterized by large pectoral fins mounted high on the body and denticulated bony plates on the head and jaws. They lived from the Devonian into the Carboniferous. The elongated pectorals had denticles along the leading edge which may have had a role in mating. They are thought to have been able to move their pectorals in a vertical plane,”flying” through the water much like modern-day penguins. Some researchers believe tey were capable of escaping predators by gliding the way the flying fish Exocoetus does today. The closest modern-day relatives of the Iniopterygii are the Chimaeras (Chimaeriformes) also known as ghost sharks or rat fish. This is an excellent part/counterpart example preserved in lateral aspect of a fine juvenile specimen. Note even at such a small size that the prominent pectoral fins are quite evident.

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