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
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 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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