At more than 2 metres (6.6 ft) in size, it is the largest known member of the Amiidae, 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 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.[1]
It is known from a holotype comprising nearly complete skull with a partial skeleton found in the Fort Union Formation in Montana, USA. This specimen was previously assigned to the species Amia uintaensis, a taxon now considered a nomen vanum. 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.[1]
A. basiloides inhabited a subtropical freshwater swamp habitat in the interior of the North American continent. It shared this habitat with a very large Acipensersturgeon, as well as the large choristoderesChampsosaurus and Kosmodraco. Numerous terrestrial fauna, including large mammals, also inhabited this habitat.[1]
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