Cyclurus (Ancient Greek for "rounded tail") is an extinct genus of freshwater Amiidae Actinopterygii known from the Late Cretaceous to the Rupelian across much of the Northern Hemisphere.
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
Thanetian and becoming particularly successful and speciose in Europe. By the Late Eocene, it was one of the last two surviving
Halecomorphi 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 (Alfred Romer & Fritiof 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 Adolph Reuss, 1844 - middle-late Eocene of the Czech Republic (Kutschlin)
-
† C. oligocenicus Winkler, 1880 - early Oligocene (Rupelian) of Germany (Sieblos)
-
† C. orientalis Meemann 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 Louis Agassiz, 1844 - late Paleocene of France (Puy de Dôme of Menat Formation). Named for Achille Valenciennes.
|left]]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
Nomen dubium 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
Amiidae 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
Percoidei 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.
