Time: Mississippian (~320 m.y.a.)
mm = 1 inch): Fish fossil is 129 mm Matrix: 225 mm by 270 mm
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 fish is a palaeoniscoid of the
genus Kalops. There are two known genera, and this one, Kalops
monophrys, is distinguished by larger size, more caudal fin rays,
and larger ganoine ridging to the bones of the head. . The detail
for a specimen nearly a third of a BILLION years old is remarkable.
Note particularly the detail to the skull, vertebral column,
and tail as well as the characteristic scale pattern.
Paleont. 76 (6), 2002, pp 1014-1028.