''Stipatosteus'' is an extinct genus of phlyctaeniid

arthrodire Arthrodira (Greek for "jointed neck") is an Order (biology), order of extinct armored, jawed fishes of the class Placodermi that flourished in the Devonian period before their sudden extinction, surviving for about 50 million years and penetratin ...

from the

Lower Devonian The Early Devonian is the first of three epochs comprising the Devonian period, corresponding to the Lower Devonian series. It lasted from and began with the Lochkovian Stage , which was followed by the Pragian from and then by the Emsian, whic ...

Belarus Belarus, officially the Republic of Belarus, is a landlocked country in Eastern Europe. It is bordered by Russia to the east and northeast, Ukraine to the south, Poland to the west, and Lithuania and Latvia to the northwest. Belarus spans an a ...

. The genus is only known from one species, being ''S. svidunovitchi'' from the Lepel Beds. ''Stipatosteus'' was the first Phlyctaenioideid to be found in the Devonian of Berlarus with only one other, '' Valentinaspis'', being described since.

Discovery

The material that would be later described as ''Stipatosteus'' is from the Korma 1 borehole drilled near the Zhlobin Saddle at depths of between 340.8 and 337.7 meters. These remains were collected with the remains of multiple species

Acanthodians Acanthodii or acanthodians is an extinct class of gnathostomes (jawed fishes). They are currently considered to represent a paraphyletic grade of various fish lineages basal to extant Chondrichthyes, which includes living sharks, rays, and c ...

along with many pieces from indeterminate vertebrates and small fragments of invertebrates.

Description

''Stipatosteus'' is estimated to only be around 40-50 mm and is only known from four pieces of the trunk armor along with a few less complete fragments. Most of these plates have tubercles with star-shaped bases which are arranged in tightly-packed rows. These tubercles would have grown on top of one another as the animal aged causing some seen on the armor to have curving and splitting ridges moving outwards from the center. The spinal plates on the sides of the trunk are long and covered in rounded tubercles with only half of the spine extending out from where they attach to the anterior ventrolateral plate. There seems to be a lack of ornamentation on the anterior ventrolateral plate from the described remains, being the only part where in doesn't appear. These plates are very short when compared to other such as '' Phlyctaenius'', being shorter than the posterior ventrolateral plates.

Classification

The trunk armor of ''Stipatosteus'' is similar to a few different groups of placoderms such as that seen in Actinolepinans though lacks anterior ventral plate. This trait, along with the length of the spinal plates, put the genus within the family

Phlyctaeniidae Phlyctaeniidae is an extinct family (biology), family of placoderm arthrodire fishes that lived during the Devonian period, mainly in Norway and North America. Classification Order Arthrodira Woodward, 1891 * Phlyctaenioidei Miles, 1973 ** Brach ...

References

{{Taxonbar, from=Q131303022 Phlyctaeniidae Placoderm genera Fossil taxa described in 2020