Phyllolepida

From Paleos

The order Phyllolepida ("leaf scales") was an order of flattened placoderms found throughout the world, with fossils being found in Devonian strata. Like other flattened placoderms, the phyllolepids were bottom-dwelling predators that ambushed prey. Unlike other flattened placoderms, the phyllolepids were inhabitants of freshwater environments.

Unlike the Rhenanida, the armor of the phyllolepids were made of whole plates, rather than numerous tubercles and scales, and unlike the Petalichthyida, the components of the extraordinarily wide mouth are known. The phyllolepids were considered to be blind, as the eyes are extremely small, so as to suggest that they were vestigial, and that they were placed on the sides of the head, as opposed to visual bottom-dwelling predators, like, say stargazers or flatfish, which have the eyes placed high on top of the head.

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. From the articulation of the thoracic and head plates, it has been suggested that they are either the sister group of order Arthrodira, or are in fact, a group of highly derived arthrodires.