The genus was named in 1995 by James D. Gardner and colleagues to unite multiple species that had at times been referred to the genera
Aspideretes or
Trionyx, all from the
Judith River Group or similar strata. The type species,
A. foveatus, was originally named as a species of
Trionyx by
Joseph Leidy in 1956, with the
type specimen being a partial
carapace and
plastron, but referred specimens covering all regions of the skeleton as well as the
skull. It is known definitively from the
Judith River Formation and equivalent strata, the
Two Medicine Formation, and probably the
Hell Creek Formation, with unsubstantiated reports of
A. foveatus suggest it may have lived beyond the end of the Cretaceous into the
Paleocene or even
Eocene. The second species,
A. splendidus, was originally named as a species of
Aspideretes by
Oliver Hay in 1908 for an incomplete carapace, but is now also known from complete carapaces, plastrons, and skulls from the
Judithian of
Montana and
Alberta. The third species,
A. allani, was originally named by
Charles W. Gilmore in 1923 as a species of
Aspideretes known from a nearly complete skeleton and skull, with additional referred elements. It is only known from the
Dinosaur Park Formation. The three species can be distinguished by multiple features of the carapace, plastron, and jaws. == Taxonomy ==