''Coriops'' is an extinct genus of freshwater osteoglossomorph fish, possibly a hiodontiform, with a single species (''C. amnicolus'') known from the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

of western North America.

Taxonomy

Sepkoski's compendium of marine fossil genera has it classified as an

eel Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 20 families, 164 genera, and about 1000 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...

, but it has also been previously classified in the Elopiformes and the

Osteoglossomorpha Osteoglossomorpha is a group of bony fish in the Teleostei. Notable members A notable member is the arapaima (''Arapaima gigas''), the largest freshwater fish in South America and one of the largest bony fishes alive. Other notable members inclu ...

. More recent studies have affirmed it as being an osteoglossomorph, and have suggested that it may be a relative of the extant mooneyes (Hiodontidae). An indeterminate hiodontid specimen (found alongside the '' Raptorex'' holotype) from the

Nemegt Formation The Nemegt Formation (also known as Nemegtskaya Svita) is a geological formation in the Gobi Desert of Mongolia, dating to the Late Cretaceous. The formation consists of river channel sediments and contains fossils of fish, turtles, crocodilians ...

Mongolia Mongolia is a landlocked country in East Asia, bordered by Russia to the north and China to the south and southeast. It covers an area of , with a population of 3.5 million, making it the world's List of countries and dependencies by po ...

was found to share close similarities with both '' Hiodon'' and ''Coriops''.

Distribution

Fossils of an indeterminate ''Coriops'' species are known as early as the

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

of the

Naturita Formation The Naturita Formation is a classification used in western Colorado and eastern Utah for a Cretaceous Period sedimentary geologic formation. This name was "applied to the upper or carbonaceous part of Dakota Group" by R.G. Young in 1960, namin ...

in Grand Staircase-Escalante National Monument in

Utah Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a border with Arizona, Colorado, and New Mexico. It also borders Wyoming to the northea ...

, USA. Fossils of the species ''C. amnicolus'' become more common across a large area of North America around the

Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...

, where they are known from the

Kaiparowits Formation The Kaiparowits Formation is a sedimentary geological formation, rock formation found in the Kaiparowits Plateau in Grand Staircase–Escalante National Monument, in the southern part of Utah in the western United States. It is over 2800 feet (8 ...

of Utah, the Mesa Verde Formation of

Wyoming Wyoming ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States, Western United States. It borders Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho t ...

, and the

Dinosaur Park Formation The Dinosaur Park Formation is the uppermost member of the Belly River Group (also known as the Judith River Group), a major geologic unit in southern Alberta. It was deposited during the Campanian stage of the Late Cretaceous, between about 7 ...

& Belly River Group in

Alberta Alberta is a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...

, Canada. During the

Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...

, remains of ''C. amnicolus'' are abundant and widespread in the

Hell Creek Formation The Hell Creek Formation is an intensively studied division of mostly Upper Cretaceous and some lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The Formation (stratigraphy), formation s ...

of Montana, the Dakotas, & Wyoming. ''Coriops'' vertebrae were previously thought to have been identified from a

Late Paleocene The Thanetian is, in the International Commission on Stratigraphy, ICS Geologic timescale, the latest age (geology), age or uppermost stage (stratigraphy), stratigraphic stage of the Paleocene epoch (geology), Epoch or series (stratigraphy), Serie ...

-aged locality of the

Ravenscrag Formation The Ravenscrag Formation is a stratigraphic unit of early Paleocene Geochronology, age in the Western Canadian Sedimentary Basin, Western Canada Sedimentary Basin. It was named for the settlement of Ravenscrag, Saskatchewan, and was first describ ...

Saskatchewan Saskatchewan is a Provinces and territories of Canada, province in Western Canada. It is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and to the south by the ...

, Canada, which would indicate that it survived the

Cretaceous–Paleogene extinction event The Cretaceous–Paleogene (K–Pg) extinction event, also known as the K–T extinction, was the extinction event, mass extinction of three-quarters of the plant and animal species on Earth approximately 66 million years ago. The event cau ...

that killed the

dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

. However, a re-analysis of these vertebra found them to instead more likely belong to the osteoglossomorph '' Lopadichthys'', previously described from the Paleocene of Canada. The wide distribution of ''Coriops'' in the North American interior, its disappearance and reappearance in southern regions such as Utah, and its general higher abundance in high latitude formations over lower latitude ones, suggests that it may have been a northernly-distributed species whose range repeatedly expanded south during cooler climactic intervals.

References

Osteoglossomorpha Prehistoric ray-finned fish genera Late Cretaceous bony fish Late Cretaceous fish of North America Paleocene fish Cenomanian genus first appearances Campanian genera Maastrichtian genus extinctions Hell Creek fauna Fossils of Wyoming Fossils of Montana Fossils of the United States Fossils of Canada Fossil taxa described in 1969 {{Cretaceous-fish-stub

Taxonomy

Distribution

See also

References