Cyathaspidida

Cyathaspidida; Temporal range: Silurian–Early Devonian PreЄ Є O S D C P T J K Pg N
	Cyathaspis banksii reconstruction
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Superclass:	Agnatha
Class:	† Pteraspidomorphi
Subclass:	† Heterostraci
Order:	† Cyathaspidiformes
Clade:	†Cyathaspidida
Families
	Cyathaspidae ; Ariaspidae ; Ctenaspidae ;

Last updated March 22, 2019

Cyathaspidida is a taxon of extinct cyathaspidiform heterostracan agnathans whose fossils are found in Silurian to Lower Devonian marine strata of Europe and North America.^[1] In life, they are thought to be benthic animals that lived most of their lives either mostly buried in or resting directly on top of the substrate.

In biology, a taxon is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and given a particular ranking, especially if and when it is accepted or becomes established. It is not uncommon, however, for taxonomists to remain at odds over what belongs to a taxon and the criteria used for inclusion. If a taxon is given a formal scientific name, its use is then governed by one of the nomenclature codes specifying which scientific name is correct for a particular grouping.

Cyathaspidiformes is an extinct order of heterostracan vertebrates known from extensive fossil remains primarily from Silurian to Early Devonian strata of Europe, and North America, and from Early Devonian marine strata of Siberia.

Heterostraci is an extinct subclass of pteraspidomorph jawless vertebrate that lived primarily in marine and estuary environments. The first identifiable heterostracans appear in the fossil record during the early Silurian, and all, save for the Psammosteids, became extinct by the start of the late Devonian. This last group of heterostracans died out in the extinction event at the end of the Devonian.

Taxonomy

The cyathaspidids of Cyathaspidida were tadpole-like animals with drum-shaped, cigar-shaped or wedge-shaped cephalothoraxes, and were anatomically similar to several other heterostracan groups. However, with some groups, such as the traquairaspids, cardiopeltids, and corvaspidids, this similarity appears to be superficial. With other groups, namely the tolypelepidids, the similarity suggests a close relationship. The type genus of the tolypelepidids, Tolypelepis , in particular, was determined to be the sister-taxon of Cyathaspidida.^[1] Originally, the cyathaspidid genera were organized together within the family Cyathaspididae. Later, the genera were then organized into subfamilies, and these subfamilies would eventually be promoted to full familial status, including Irregularaspididae, Anglaspididae, Poraspididae, Ctenaspididae, etc. In 2013, Lundgren and Blom reassessed several specimens of cyathaspidids, and reorganized them into three families, Cyathaspidae, Ariaspidae and Ctenaspidae.^[1]

Traquairaspis is a genus of extinct heterostracan agnathan fish known from the Silurian and Early Devonian periods. It is predominantly known from Late Silurian fluvial deposits from Wales and England: some species were also found in shallow water marine environment in Canada and North America.

Tolypelepidida is an extinct order of heterostracan vertebrates. These armored jawless fish superficially resemble their relatives, the cyathaspids, though, researchers place the tolypelepids as a sister group to the cyathaspids and the pteraspidids. A recent study by Lundgren and Blom in 2013 implies that the order is paraphyletic, with the type genus, Tolypelepis, being the sister taxon of Cyathaspidiformes. The typical tolypelepid had a carapace formed from dorsal and ventral plates, and a scaly tail.

Cyathaspidae

Cyathaspidae contains most of the genera originally contained within Cyathaspididae, as well as those genera contained within Irregularaspididae, and Poraspididae. In addition to the type genus, Cyathaspis , Cyathaspidae contains the following genera: Americaspis , Archegonaspis , Capitaspis , Dikenaspis , Dinaspidella , Homaspidella , Irregulareaspis , Nahanniaspis , Pionaspis , Poraspis , Ptomaspis , Seretaspis , Steinaspis , Torpedaspis , and Veronaspis .

Cyathaspis is the type genus of the heterostracan order Cyathaspidiformes. Species are found in late Silurian strata in Europe, especially in Great Britain and Gotland, Sweden. The living animal would have looked superficially like a tadpole, albeit covered in bony plates composed of the tissue aspidine, which is unique to heterostracan armor.

Capitaspis is an extinct genus of cyathaspidine cyathaspidid heterostracan jawless vertebrate known from the Late Silurian Somerset Island Formation of the Northwest Territories, Canada. It contains a single species, Capitaspis giblingi. It is most closely related to Pionaspis.

Poraspis is an extinct genus of heterostracan. Fossils are found in Late Silurian and Early Devonian marine strata of Norway, Canada and the United States.

Ariaspidae

Family Ariaspidae contains Ariaspis , and its sister-taxa originally contained within Anglaspididae/Anglaspidinae, including Anglaspis , Listraspis , Liliaspis , and Paraliliaspis .

Ariaspis is an extinct genus of cyathaspidiform heterostracan agnathan. Fossils are found in marine strata of Canada and Europe from the late Silurian period until its extinction during the Early Devonian. A new species, A. arctata, was described by David K. Elliott and Sandra Swift in 2010.

Anglaspis is an extinct genus of cyathaspidiform heterostracan agnathan. Fossils are found in marine strata of Europe, from the late Silurian period until genus' extinction during the Early Devonian. As with other cyathaspidiforms, individuals of Anglaspis had dorsal and ventral plates covering the forebody, gill pouches, and nasal openings that lay on the roof of the oral cavity.

Liliaspis philippovae is an extinct cyathaspidiform heterostracan agnathan from early Devonian marine strata of the Ural Mountains.

Ctenaspidae

If Amphiaspidida can be ignored as a daughter-taxon, the family Ctenaspidae contains Ctenaspis and its various sister-taxa originally contained within both Ctenaspididae and Ctenaspididae, including Allocryptaspis , Alainaspis , Zaphoctenaspis , Arctictenaspis , and Boothiaspis , which was first described as a "Canadian amphiaspid."

Amphiaspidida is a taxon of extinct cyathaspidid heterostracan agnathans whose fossils are restricted to Lower Devonian marine strata of Siberia near the Taimyr Peninsula. Some authorities treat it as a suborder of Cyathaspidiformes, while others treat it as an order in its own right as "Amphiaspidiformes." In life, they are thought to be benthic animals that lived most of their lives mostly buried in the sediment of a series of hypersaline lagoons. Amphiaspids are easily distinguished from other heterostracans in that all of the plates of the cephalothorax armor are fused into a single, muff-like unit, so that the forebody of the living animal would have looked like a potpie or a hot waterbottle with a pair of small, or degenerated eyes sometimes flanked by preorbital openings, a pair of branchial openings for exhaling, and a simple, slit-like, or tube-like mouth.

Ctenaspis is an extinct genus of heterostracan cyathaspid agnathans from the early Devonian of Canada.

Alainaspis platyrhina is an extinct cyathaspidid heterostracan agnathan vertebrate which existed in a marine environment in what is now the Northwest Territories of Canada, during the upper Silurian period. It was first named by David Elliott and David Dineley in 1985, and is placed in the monotypic genus Alainaspis, closely related to Boothiaspis.

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References

1 2 3 Lundgren, Mette, and Henning Blom. "Phylogenetic relationships of the cyathaspidids (Heterostraci)." GFF 135.1 (2013): 74-84.

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[lundgren-1] 1 2 3 Lundgren, Mette, and Henning Blom. "Phylogenetic relationships of the cyathaspidids (Heterostraci)." GFF 135.1 (2013): 74-84.

Cyathaspidida Temporal range: Silurian–Early Devonian PreЄ Є O S D C P T J K Pg N

Cyathaspis banksii reconstruction
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Superclass:	Agnatha
Class:	† Pteraspidomorphi
Subclass:	† Heterostraci
Order:	† Cyathaspidiformes
Clade:	†Cyathaspidida
Families
Cyathaspidae Ariaspidae Ctenaspidae