Seven species have been referred to this genus over the years, which have since been reassigned to other genera:
- Palaeoscincus africanus, named by Robert Broom in 1910/1912, a partial jaw from the Tithonian-Valanginian-age Upper Jurassic-Lower Cretaceous Kirkwood Formation of South Africa, now known as the stegosaurid Paranthodon;
Palaeoscincus asper, "the rough one", a dubious tooth taxon from the late Campanian-age Upper Cretaceous Dinosaur Park Formation of Alberta, Canada, named by Lawrence Morris Lambe in 1902, based on a single tooth, specimen NMC 1349 now referred to Euoplocephalus;
- Palaeoscincus costatus, "the ribbed one", the type species named by Leidy in 1856, known from a single tooth, specimen ANSP 9263 found by Ferdinand Vandiveer Hayden near Fort Benton. It was the first ankylosaurian species to be named based on American material; It is now considered an ankylosaurian of unknown affinities.
- Palaeoscincus latus, "the wide one" named by Othniel Charles Marsh in 1892, from the late Maastrichtian-age Upper Cretaceous Lance Formation of Wyoming, also based on a single tooth, specimen YPM 4810 found in Niobrara County, Wyoming, now believed to have come from a pachycephalosaurid;
- "P. magoder", a nomen nudum name from a faunal list by Karl ("Charles") L. Henning, the result of mistaking the German words mag oder for a specific name;
- Palaeoscincus rugosidens, "rough tooth" named by Charles Whitney Gilmore in 1930, the best-known species, a skull and partial skeleton from the late Campanian-age Two Medicine Formation of Montana, now known as Edmontonia rugosidens, or a separate genus Chassternbergia. It was this species that was portrayed in most restorations of the genus.
- Palaeoscincus tutus, a renaming of Euoplocephalus tutus by Edwin Hennig in 1915.
Today, the type species P. costatus and thereby the genus is considered to be an indeterminate ankylosaurian, perhaps an indeterminate nodosaurid.