Pteraspidomorphi

Pteraspis, live reconstruction

• Worldwide

The Pteraspidomorphi or Pteraspidomorpha are primitive jawless vertebrates ( Vertebrata ), who lived from early Ordovician to late Devonian million years ago, about 479-376 ( mya ).

Features

The fossils of this taxon show a strong armor of the head, which is formed by plates of dermal bones, which consist of aspidin. The Pteraspidomorphi inhabited the sea, mostly near the coast, but it is believed that some forms have penetrated into the fresh water. The skeleton is cartilaginous, only the Eriptychiida and possibly at the Arandaspida traces show calcification. Except for the tail fin, the body has no other fins.

System

The Pteraspidomorphi were long regarded as the jawed fish or pine mouths ( gnathostomata ) -affiliated group, the common features ( synapomorphies ) of this group provide but for the purposes of phylogenetic systematics original features ( plesiomorphies ), which they share with other groups.

Pteraspidomorphi within three to four sub- groups:

• The Arandaspida, also called Arandaspidida, have exclusively marine representatives. The oldest representative Arandaspis comes from the upper Unterordovizium from Australia. Another well-known fossil is of about 40 centimeters long Sacabambaspis janvieri from South America.

• The Astraspida, also called Astraspidida are also exclusively marine and come as most Arandaspidida from the Middle Ordovician about 460 million years ago.

• The Heterostraci are the youngest group of Pteraspidomorphi and of fossils from the Silurian and Devonian sediments known. The locations are in North America, Europe and Siberia.

The fourth group consists exclusively of the known only from fragmentary remains genus Eriptychius that stands as Eriptychiida equal to the other or the Astraspida is assigned.