It is well known, with many fossils having been collected from the Chadron and Brule Formations in South Dakota.

The species was first named in 1904, but was originally classified as a crocodile in the genus Crocodilus.

In 1930, American paleontologist George Gaylord Simpson considered A. prenasalis (then called Caimanoidea) to be ancestral to A. mooki because it appeared to be similar but less specialized.

Simpson hypothesized that A. prenasalis appeared at this time and gave rise to A. mooki, which soon became extinct.

This was called the "law of the unspecialized", first devised by paleontologist Edward Drinker Cope in 1896.