Cyclurus

''Cyclurus'' (Ancient Greek for "rounded tail") is an extinct genus of freshwater amiid ray-finned fish known from the Late Cretaceous to the Early Oligocene across much of the Northern Hemisphere. It is thought to be the closest relative of the extant bowfins in the genus '' Amia'', although species of ''Cyclurus'' were significantly smaller in size compared to ''Amia''.

Evolution

Remains of ''Cyclurus'' are first known from western North America during the Maastrichtian stage of the Cretaceous with the species ''C. fragosus'', with the genus having presumably diverged from '' Amia'' shortly before. Potential earlier remains are known from the Campanian. Alongside ''Amia'', ''Cyclurus'' survived the Cretaceous-Paleogene extinction event in a refugium in western North America. Shortly afterwards, it saw a dramatic range expansion over the Paleogene, colonizing Europe and Asia by the Late Paleocene and becoming particularly successful and speciose in Europe. By the Late Eocene, it was one of the last two surviving halecomorph genera, alongside ''Amia''. However, alongside most ''Amia'' species aside from those in eastern North America, it became extinct during the Oligocene.

Taxonomy

The following species are known:

* †''C. efremovi'' (Sytchevskaya, 1981) - late Paleocene of Mongolia ( Naran Bulak Formation) (=''Amia efremovi'' Sytchevskaya, 1981). Named for Ivan Yefremov.
* †''C. fragosus'' (Jordan, 1927) - Late Cretaceous (Maastrichtian) of Alberta, Canada (Scollard Formation) and Montana, North Dakota, South Dakota and Wyoming, USA (Hell Creek Formation, Fox Hills Formation) (=''Kindleia fragosa'' Jordan, 1927)
* †''C. gurleyi'' (Romer & Fryxell, 1928) - early Eocene (Ypresian) of Wyoming, USA (Fossil Butte of Green River Formation) (=†''Paramiatus gurleyi'' Romer & Fryxell, 1928)
* †''C. ignotus'' ( Blainville, 1818) - late Eocene (Priabonian) of France (Montmartre) (=†"''Amia''" ''ignota'' Blainville, 1818)
* †''C. macrocephalus'' Reuss, 1844 - middle-late Eocene of the Czech Republic (Kutschlin)
* †''C. oligocenicus'' Winkler, 1880 - early Oligocene (Rupelian) of Germany (Sieblos)
* †''C. orientalis'' Chang, Wang & Wu, 2010 - early-mid Eocene of Hunan, China ( Xiawanpu Formation)
* †''C. kehreri'' (Andreae, 1893) - middle Eocene (Lutetian) of Germany (Messel Formation & Geiseltal Formation) (=''Amia kehreri'' Andreae, 1893)
* †''C. valenciennesi'' Agassiz, 1844 - late Paleocene of France (Puy de Dôme of Menat Formation). Named for Achille Valenciennes.
The species †''C.'' "''lacus''" (Russell, 1928) (=†''Stylomyleodon lacus'' Russell, 1928) from the middle Paleocene of Alberta, †''C.'' "''chinzhalensis''" (Sytchevskaya, 1986) (=†''Amia chinzhalensis'' Sytchevskaya, 1986) from the mid-late Eocene of Kazakhstan, and †''C.'' "''russelli''" (Janot, 1966) (=†"''Amia''" ''russelli'' Janot, 1966) from the late Paleocene of France are considered ''nomina dubia'' due to insufficiently diagnostic remains. The Geiseltal specimens of ''C. kehreri'' differ morphologically from the Messel ones, and may represent a distinct species. Indeterminate ''Cyclurus'' remains are known from the middle Eocene of Jilin, China, the late Paleocene Ravenscrag Formation of Saskatchewan & the Maastrichtian Horseshoe Canyon Formation of Alberta, Canada, and possibly the Campanian-aged Aguja Formation of Texas, USA.

Paleoecology

''C. kehreri'' is the most common fossil fish known from the Messel pit, and in fact the most abundant fossil amiid in the world, with thousands of specimens recovered. Fossils of ''C. kehreri'' are known representing different growth stages. Almost no specimens of ''C. kehreri'' are known with fish bones in their stomach (a specimen with percoid bones in its stomach is thought to have likely scavenged on them), suggesting that unlike other amiids, ''Cyclurus'' likely fed on small invertebrates instead of other fish. However, more recently, two ''C. kehreri'' specimens have been discovered with specimens of the bat ''Palaeochiropteryx'' caught in their mouths, suggesting that they either opportunistically attacked the dying bats or attempted scavenging on them, although these attempts were unsuccessful.

Contrasting with ''C. kehreri'''s abundance, ''C. gurleyi'' is one of the rarest fishes from the Green River Formation, with only 8 specimens known from the hundreds of thousands of fossil fishes excavated.

References

{{Taxonbar, from=Q17628456

†
Prehistoric ray-finned fish genera
Late Cretaceous fish of North America
Late Cretaceous bony fish
Paleogene fish of North America
Paleogene fish of Europe
Paleogene fish of Asia
Maastrichtian genus first appearances
Thanetian genera
Ypresian genera
Lutetian genera
Priabonian genera
Rupelian genus extinctions
Fossils of Canada
Fossils of the United States
Hell Creek fauna
Fossils of France
Fossils of Germany
Fossils of the Czech Republic
Fossils of Kazakhstan
Fossils of Mongolia
Fossils of China
Fossil taxa described in 1844
Taxa named by Louis Agassiz