''Aponileus'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the At ...

s. Chung-Hung Hu

circumscribed In geometry, the circumscribed circle or circumcircle of a polygon is a circle that passes through all the vertices of the polygon. The center of this circle is called the circumcenter and its radius is called the circumradius. Not every polyg ...

the genus in 1963. The genus was once considered a

junior subjective synonym The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linn ...

of the genus '' Psephosthenaspis'' but it is considered to be a distinct genus again. , fossils have been found in Greenland, Texas, and Utah. They all date to the Upper

Floian The Floian is the second stage of the Ordovician Period. It succeeds the Tremadocian with which it forms the Lower Ordovician epoch. It precedes the Dapingian Stage of the Middle Ordovician. The Floian extended from to million years ago. The lowe ...

(Blackhillsian) within the

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

Period.

Taxonomic history

''Aponileus'' was initially

by Chung-Hung Hu in 1963. The

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

is ''A. latus'', also described by Hu in 1963. The type material was poorly preserved. Hu initially said that ''Aponileus'' is "most like '' Nileus''", i.e., treating it as a nileid. Subsequently, this genus received "virtually no mention" in the trilobite literature for many years, aside from C. P. Hughes's 1979 assessment that two specimens which Lehi F. Hintze had tentatively assigned to '' Barrandia'' in 1953 should be placed in ''Aponileus''. In 2003, Jonathan M. Adrain synonymized ''Aponileus'' with '' Psephosthenaspis'', placing it in the family Bathyuridae. In 2012, Adrain and Neo E. B. McAdams treated ''Aponileus'' as a distinct genus within Bathyuridae. They also included the species ''A. glaber'', which Christian Poulsen had initially described in the genus ''

Bolbocephalus ''Bolbocephalus'' is a genus of proetid trilobites in the family Bathyuridae. Species lived during the early part of the Arenig stage of the Ordovician Period, a faunal stage which lasted from approximately 478 to 471 million years ago, in mar ...

'' in 1927. Adrain and McAdams placed five newly described species in ''Aponilus'', namely ''A. aasei'', ''A. belkaae'', ''A. laikaae'', ''A. strelkaae'', and ''A. ugolekae''; they also tentatively assigned a further newly described species to this genus: ''A.''? ''veterokae''. While they believed the "best supported current hypotheses" was to place it in ''Aponileus'', they acknowledged it is "very different from all other species included in the genus" and hence "assign dthe species only with question". Various

specific epithet In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...

s are named after

Soviet space dogs During the 1950s and 1960s the Soviet space program used dogs for sub-orbital and orbital space flights to determine whether human spaceflight was feasible. In this period, the Soviet Union launched missions with passenger slots for at le ...

Laika Laika (russian: link=no, Лайка; – 3 November 1957) was a Soviet space dog who was one of the first animals in space and the first to orbit the Earth. A stray mongrel from the streets of Moscow, she flew aboard the Sputnik 2 spacecra ...

, Belka, Strelka, Ugolyok, and Veterok.

Phylogeny

In 2012, Adrain and McAdams said they believed that ''Aponileus'' was likely related to the "''Acidiphorus'' group", but said that the

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

remained unclear. While ''Psephosthenaspis'' resembles ''Aponileus'', Adrain and McAdams believe they belong to distinct

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

s. ''Aponileus laikaae'' is the basal species.

Distribution

Chronologically, ''Aponileus'' is found entirely within the

Lower Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. The ...

, specifically the upper

(Blackhillsian). The genus's type species, ''A. latus'', has found in the El Paso Formation within the Franklin Mountains of west Texas. ''A. glaber'' was found in

Washington Land Washington Land is a peninsula in northwestern Greenland. It is a part of the Avannaata municipality. Washington Land was explored in the 19th century. Traditionally it was one of the hunting grounds of the Inuit, but there are archaeological rem ...

, in northwestern Greenland. The remaining species, which Adrain and McAdams first described in 2012, are all from the

Confusion Range The Confusion Range is a north-south trending mountain range in west-central Utah, United States. It is bounded by Snake Valley to the west, Tule Valley to the east, the Great Salt Lake Desert to the north, and the Ferguson Desert to the south. ...

Millard County, Utah Millard County ( ) is a county in the U.S. state of Utah. As of the 2010 United States Census, the population was 12,503. Its county seat is Fillmore, and the largest city is Delta. History The Utah Territory legislature created the county on ...

Species

, the following species are recognized: * '' A. latus'' — Texas * '' A. aasei'' — Utah * '' A. glaber'' — Greenland * '' A. laikaae'' — Utah * '' A. belkaae'' — Utah * '' A. strelkaae'' — Utah * '' A. ugolekae'' — Utah * ''A.''? ''veterokae'' — Utah

References

Works cited