Auchenaspis salteri is an extinct species of armored jawless fish

Osteostraci

The class Osteostraci was a group of bony-armored jawless fish, termed "ostracoderms", that lived in what is now North America, Europe and Russia from the Middle Silurian to Late Devonian....

 of the order

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 Thyestiida from the Late Silurian

Silurian

The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...

 of England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

. In England, A. salteri's fossils are found in extreme abundance in the Lower Old Red Sandstone strata in Ledbury

Ledbury

Ledbury is a town in Herefordshire, England, lying east of Hereford, and south of the Malvern Hills.Today, Ledbury is a thriving market town in rural England. The town has a large number of timber framed buildings, in particular along Church Lane and High Street. One of Ledbury's most outstanding...

, Herefordshire

Herefordshire

Herefordshire is a historic and ceremonial county in the West Midlands region of England. For Eurostat purposes it is a NUTS 3 region and is one of three counties that comprise the "Herefordshire, Worcestershire and Gloucestershire" NUTS 2 region. It also forms a unitary district known as the...

.

A. salteri strongly resembles the thyestiids Procephalaspis

Procephalaspis

Procephalaspis is an extinct genus of jawless fish.-References:* Telling the Evolutionary Time: Molecular Clocks and the Fossil Record by Philip C J Donoghue and M. Paul Smith...

and Thyestes

Thyestes

In Greek mythology, Thyestes was the son of Pelops and Hippodamia, King of Olympia, and father of Pelopia and Aegisthus. Thyestes and his twin brother, Atreus, were exiled by their father for having murdered their half-brother, Chrysippus, in their desire for the throne of Olympia...

, and within Thyestiida, it represents a transitional form between the primitive, superficially Cephalaspis

Cephalaspis

Cephalaspis was a genus of armored goldfish-sized to trout-sized detritivorous fish that lived in freshwater streams and estuaries of early Devonian Western Europe...

-like forms, such as Thyestes

Thyestes

In Greek mythology, Thyestes was the son of Pelops and Hippodamia, King of Olympia, and father of Pelopia and Aegisthus. Thyestes and his twin brother, Atreus, were exiled by their father for having murdered their half-brother, Chrysippus, in their desire for the throne of Olympia...

, and the more specialized tremataspid thyestiids, like Tremataspis

Tremataspis

Tremataspis is an extinct genus of primitive jawless fish from the Silurian period of what is now Estonia.An osteostracid, Tremataspis was about in length, and had an armored shield covering its head. Compared with its relatives, the shield was unusually elongated, covering the whole front of the...

, Dartmuthia

Dartmuthia

Dartmuthia is an extinct genus of primitive jawless fish that lived in the Silurian period in what is now Estonia.To date only the creature's armored head shield has been found. Since the mouth is positioned on the underside of the head Dartmuthia is presumed to have dwelled on the ocean floor,...

, or Dobraspis, whose headshields tend to resemble hot buns or horseshoe crabs.