Unlike other flattened placoderms, the phyllolepids were inhabitants of freshwater environments.

Despite having a relatively clear idea of the phyllolepids' lifestyle and anatomy, most fossils consist of fragments of their thoracic armor, and only two genera, Phyllolepis and Austrophyllolepis have been thoroughly studied.

The Phyllolepids are divided into two families, the more primitive Gavinaspididae, represented only by Gavinaspis of Early Devonian China, and Phyllolepididae, which contains all other genera.

Barring the Chinese Gavinaspis, the cosmopolitan Placolepis (fossils of which have been found in Australia, Turkey, Venezuela, and Antarctica), and the Euro-North American Phyllolepis, the majority of genera are found in Early to Middle Devonian Australia.

The Rise of Fishes: 500 Million Years of Evolution Baltimore: The Johns Hopkins University Press, 1996.