The order Phyllolepida ("leaf scales") was an order of flattened placoderms found throughout the world, with fossils being found in Devonian

Devonian

The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 strata

Stratum

In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...

. 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

Rhenanida

Rhenanida was an order of primitive, lightly armored placoderms. Unlike most other placoderms, the rhenanids' armor was made up of a mosaic of unfused scales and tubercles...

, the armor of the phyllolepids were made of whole plates, rather than numerous tubercles and scales, and unlike the Petalichthyida

Petalichthyida

The Petalichthyida was an order of small, flattened placoderm fish. They were typified by their splayed fins, and numerous tubercles that decorated all of the plates and scales of their armor. They reached a peak in diversity during the Early Devonian and were found throughout the world,...

, the components of the extraordinarily wide mouth are known. The phyllolepids are considered to have been blind, as the eyes are extremely small, so much 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 stargazer

Stargazer

The stargazers are a family Uranoscopidae of perciform fish that have eyes on top of their heads . The family includes about 50 species in 8 genera, all marine and found worldwide in shallow waters....

s or flatfish

Flatfish

The flatfish are an order of ray-finned fish, also called the Heterosomata, sometimes classified as a suborder of Perciformes. In many species, both eyes lie on one side of the head, one or the other migrating through and around the head during development...

, 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

Thorax

The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...

 armor, and only two genera

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

, Phyllolepis

Phyllolepis

Phyllolepis is the type genus of Phyllolepida, an extinct order of placoderm fish from the Devonian.Phyllolepis lived in freshwater environments, possibly rivers and streams...

and Austrophyllolepis

Austrophyllolepis

Austrophyllolepis is an extinct genus of placoderm.-References:*...

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

Arthrodira

Arthrodira is an order of extinct armoured jawed fishes of the Placodermi class that flourished in the Devonian period before their sudden extinction, surviving for about 50 million years and penetrating most marine ecological niches....

, or are in fact, a group of highly derived arthrodires.