Cyathaspidiformes is an extinct

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

heterostracan Heterostraci (Ancient Greek, ἕτερος+ὄστρακον "those itha different shell" i is pl. of -us is an extinct subclass of pteraspidomorph jawless vertebrate that lived primarily in marine and estuary environments. Heterostraci exi ...

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

s known from extensive fossil remains primarily from

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...

to Early

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

strata of

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

, and

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

, and from Early

marine strata of

Siberia Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of ...

Anatomy

Like their descendants, the pteraspidids, all cyathaspidiform heterostracans had the cephalothorax enclosed in armor, formed from several plates, including dorsal, ventral, a dorsal spine derived from a scale, and a large, scale-covered tail. Thus, the living animals would have resembled tadpoles encased in massive armor. The majority of taxa have the

rostral Rostral may refer to: Anatomy * Rostral (anatomical term), situated toward the oral or nasal region * Rostral bone, in ceratopsian dinosaurs * Rostral organ, of certain fish * Rostral scale, in snakes and scaled reptiles Other uses * Rostral colu ...

and

pineal The pineal gland, conarium, or epiphysis cerebri, is a small endocrine gland in the brain of most vertebrates. The pineal gland produces melatonin, a serotonin-derived hormone which modulates sleep patterns in both circadian and seasonal cycle ...

plates fused or merged with the dorsal plate, and in the amphiaspidids, all the plates of the cephalothorax were fused together into a single "muff-like" unit. Unlike the pteraspidids, all cyathaspidiforms are thought to be almost uniformly benthic in lifestyle, though only the amphiaspids and the ctenaspids are thought to be burrowers.

Taxonomy

The taxonomy of Cyathaspidiformes is a convoluted affair, as taking into account of several of the various problematic heterostracan taxa which strongly or superficially resemble cyathaspidiforms, such as ''

Cardipeltis ''Cardipeltis'' is an extinct genus of heterostracan agnathan from marine strata of early Devonian of Utah, and Wyoming Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to t ...

,'' '' Traquairaspis'', '' Corvaspis'' and

Tolypelepidida Tolypelepidida is an extinct order (biology), order of heterostraci, heterostracan vertebrates. These armored jawless fish superficially resemble their relatives, the Cyathaspidiformes, cyathaspids, though, researchers place the tolypelepids as ...

, Cyathaspidiformes appears to be

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of converg ...

. Phylogenetic analyses suggest that the tolypelepidid genera, including '' Athenaegis'', '' Asketaspis'', and in particular, '' Tolypelepis'', are the sister-taxa of cyathaspidiforms.Lundgren, Mette, and Henning Blom. "Phylogenetic relationships of the cyathaspidids (Heterostraci)." GFF 135.1 (2013): 74-84. Even within the order, there is much debate about organizing the taxa. Until recently, there were several families within the suborder

Cyathaspidida 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.Lundgren, Mette, and Henning Blom. "Phylogenetic relationships of the cy ...

, including Cyathaspididae, Irregularaspididae, Anglaspididae, Poraspididae, etc. In a phylogenetic survey in 2013 by Lundgren and Blom, the various families and genera within Cyathaspidida are reorganized into three families, Cyathaspidae, Ctenaspidae, and

Ariaspidae Ariaspidae is a family of extinct cyathaspidiform heterostracan agnathans in the suborder Cyathaspidida. Family Ariaspidae contains ''Ariaspis ''Ariaspis'' is an extinct genus of cyathaspidiform heterostracan agnathan. Fossils are found ...

. The suborder Amphiaspidida, traditionally thought of as the daughter or sister-taxon of Ctenaspididae/Ctenaspidae, was excluded from this particular survey, as, while the authors did not directly challenge this idea, they excluded Amphiaspidida from the survey, noting that that group was "extremely derived and virtually impossible" to be of any use to this survey.

Taxa

Cyathaspidiformes is divided into two suborders, Cyathaspidida and Amphiaspidida. The former has the cephalothorax armor divided into several plates, while the latter have the cephalothorax armor fused into a single "muff-like" unit.

Cyathaspidida

Typical cyathaspidid heterostracans were fusiform or cigar-shaped animals. Their fossils are found in Silurian and early Devonian marine and marginal marine strata of North America, Europe, and the Ural Mountains. '' Kiangsuaspis'', from Silurian Chinese marine strata, was originally thought to be a Chinese cyathaspidid, until it was then reappraised as a

phyllocarid Phyllocarida is a subclass of crustaceans, comprising the extant order Leptostraca and the extinct orders Hymenostraca and Archaeostraca. See also *''Ceratiocaris'' *''Cinerocaris'' *''Vladicaris ''Vladicaris'' is an arthropod known from the ...

crustacean. Currently, the taxa of this suborder are divided into three families.

Cyathaspidae

Cyathaspidae encompasses the taxa of the families Cyathaspididae, Irregularaspididae, and Poraspididae.

Ariaspidae

Ariaspidae encompasses the taxa ''

Ariaspis ''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 The Devonian ( ) is a geolo ...

'' and the taxa formerly contained within Anglaspididae ('' Anglaspis'', '' Liliaspis'' and '' Paraliliaspis'').

Ctenaspidae

Ctenaspidae encompasses the ctenaspids, ('' Ctenaspis'', '' Arctictenaspis'' and '' Zaphoctenaspis''), and the allocryptaspids ('' Boothiaspis'', '' Allocryptaspis'' and '' Alainaspis''). ''Boothiaspis'', from the

Boothia Peninsula Boothia Peninsula (; formerly ''Boothia Felix'', Inuktitut ''Kingngailap Nunanga'') is a large peninsula in Nunavut's northern Canadian Arctic, south of Somerset Island. The northern part, Murchison Promontory, is the northernmost point o ...

, was originally described as a Canadian amphiaspidid. Ctenaspis NT small

Amphiaspidida

All the cyathaspidiforms of Suborder Amphiaspidida, sometimes treated as a distinct order "Amphiaspidiformes," are endemic to Lower Devonian marine strata of what is now the

Taimyr Peninsula The Taymyr Peninsula (russian: Таймырский полуостров, Taymyrsky poluostrov) is a peninsula in the Far North of Russia, in the Siberian Federal District, that forms the northernmost part of the mainland of Eurasia. Administrati ...

, in what was once a series of

hypersaline A hypersaline lake is a landlocked body of water that contains significant concentrations of sodium chloride, brines, and other salts, with saline levels surpassing that of ocean water (3.5%, i.e. ). Specific microbial species can thrive in h ...

lagoons cut off from the ocean. In addition to having the plates of the cephalothorax armor fused together to form a muff-like unit shaped like a

pot pie Pot pie is the North American term for a type of meat pie with a top pie crust that is commonly used throughout the continent. consisting of flaky pastry. Pot pies may be made with a variety of fillings including poultry, beef, seafood, or plant- ...

or a

hot water bottle A hot-water bottle is a bottle filled with hot water and sealed with a stopper, used to provide warmth, typically while in bed, but also for the application of heat to a specific part of the body. Early history Containers for warmth in bed we ...

, all amphiaspidids had a simple, slit-shaped mouth, and reduced or no eyes. These adaptations suggest that the living animals were filter- or suspension-feeders that habitually buried themselves in the substrate.

References

Devonian jawless fish Silurian jawless fish Prehistoric jawless fish orders Heterostraci Devonian fish of Asia Silurian fish of Asia Devonian fish of Europe Silurian fish of Europe Devonian fish of North America Silurian fish of North America Fossils of Russia Silurian first appearances Pridoli taxonomic orders Early Devonian taxonomic orders Devonian extinctions {{Paleo-jawless-fish-stub