''Amia basiloides'' is an extinct species of giant

bowfin The ruddy bowfin (''Amia calva'') is a ray-finned fish native to North America. Common names include mudfish, mud pike, dogfish, grindle, grinnel, swamp trout, and choupique. It is regarded as a relict, being one of only two surviving species ...

that inhabited western

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

during the

Middle Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek ...

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 ...

, about 5-10 million years after the Cretaceous-Paleogene extinction event. The species name originates from the

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

βασιλεύς (''

basileus ''Basileus'' () is a Greek term and title that has signified various types of monarchs throughout history. In the English language, English-speaking world, it is perhaps most widely understood to mean , referring to either a or an . The title ...

''), meaning "king", referencing its immense size.

Discovery

It is known from a

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

comprising nearly complete skull with a partial skeleton found in the

Fort Union Formation The Fort Union Formation is a geologic unit containing sandstones, shales, and coal beds in Wyoming, Montana, and parts of adjacent states. In the Powder River Basin, it contains important economic deposits of coal, uranium, and coalbed methane. ...

Montana Montana ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Idaho to the west, North Dakota to the east, South Dakota to the southeast, Wyoming to the south, an ...

, USA. This specimen was previously assigned to the species ''Amia uintaensis'', a taxon now considered a ''

nomen vanum This is a list of terms and symbols used in scientific names for organisms, and in describing the names. For proper parts of the names themselves, see List of Latin and Greek words commonly used in systematic names. Many of the abbreviations are ...

''. An isolated vertebra is also known from another Fort Union Formation locality, which appears to represent an individual 20 to 30 percent larger than the holotype individual.

Description

At more than in size, it is one of the largest known member of the

Amiidae The Amiidae are a family of basal ray-finned fishes. The bowfin and the eyespot bowfin ('' Amia ocellicauda'') are the only two species to survive today, although additional species in all four subfamilies of Amiidae are known from Jurassic, Cre ...

, and one of the largest holosteans known to have existed. The only bowfin relative known to rival it in size was the slightly smaller

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 ...

amiid '' Melvius''. Its large size was likely related to the extinction of ''Melvius'' and other vidalamiines during the K-Pg extinction, opening up new ecological niches. It appears to have been an early-diverging member of the genus ''Amia'', being more derived than '' A. hesperia'', but more basal than all other members of the group, including extant bowfin species.

Paleoecology

''A. basiloides'' inhabited a subtropical freshwater swamp habitat in the interior of the North American continent. It shared this habitat with a very large ''

Acipenser ''Acipenser'' is a genus of sturgeons, containing three species native to freshwater and estuarine systems of eastern North America and Europe. It is the type genus of the family Acipenseridae and the order Acipenseriformes. Taxonomy Prior t ...

sturgeon Sturgeon (from Old English ultimately from Proto-Indo-European language, Proto-Indo-European *''str̥(Hx)yón''-) is the common name for the 27 species of fish belonging to the family Acipenseridae. The earliest sturgeon fossils date to the ...

, as well as the large choristoderes ''

Champsosaurus ''Champsosaurus'' is an extinct genus of crocodile-like choristodere reptile, known from the Late Cretaceous and early Paleogene periods of North America and Europe (Campanian–Paleocene). The name ''Champsosaurus'' is thought to come from , () ...

'' and '' Kosmodraco''. Numerous terrestrial fauna, including large mammals, also inhabited this habitat.

References

{{taxonbar, from1=Q125924987 †basiloides Paleocene fish Paleogene fish of North America Fossils of Montana Taxa named by Thomas J. Near Fossil taxa described in 2024