Hyperoartia or Petromyzontida is a disputed group of

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, with c ...

s that includes the modern

lamprey Lampreys (sometimes inaccurately called lamprey eels) are an ancient extant lineage of jawless fish of the order Petromyzontiformes , placed in the superclass Cyclostomata. The adult lamprey may be characterized by a toothed, funnel-like s ...

s and their

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

relatives. Examples of hyperoartians from early in their fossil record are '' Endeiolepis'' and '' Euphanerops'' (which possessed a calcified branchial basket), fish-like animals with

hypocercal tail Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as s ...

s that lived during the Late Devonian Period. Some

paleontologists Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of foss ...

still place these forms among the "

ostracoderm Ostracoderms () are the armored jawless fish of the Paleozoic Era. The term does not often appear in classifications today because it is paraphyletic (excluding jawed fishes) (may also be polyphyletic if anaspids are closer to cyclostomes) an ...

s" (jawless armored fishes) of the

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...

Anaspida, but this is increasingly considered an artificial arrangement based on ancestral traits. Placement of this group among the

jawless vertebrates Agnatha (, Ancient Greek 'without jaws') is an infraphylum of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both present (cyclostomes) and extinct ( conodonts and ostracoderms) species. Among recent animals, cyclosto ...

is a matter of dispute. While today enough fossil diversity is known to make a close relationship among the "ostracoderms" unlikely, this has muddied the issue of the Hyperoartia's closest relatives. Traditionally the group was placed in a superclass

Cyclostomata Cyclostomi, often referred to as Cyclostomata , is a group of vertebrates that comprises the living jawless fishes: the lampreys and hagfishes. Both groups have jawless mouths with horny epidermal structures that function as teeth called cer ...

together with the Myxini (hagfishes). More recently, it has been proposed that the Myxini are more basal among the skull-bearing chordates, while the Hyperoartia are retained among vertebrates. But even though this may be correct, the lampreys represent one of the oldest divergences of the vertebrate lineage, and whether they are better united with some "ostracoderms" in the

Cephalaspidomorphi Cephalaspidomorphs are a group of jawless fishes named for '' Cephalaspis'' of the osteostracans. Most biologists regard this taxon as extinct, but the name is sometimes used in the classification of lampreys, because lampreys were once thought ...

, or not closer to these than to e.g. to other "ostracoderms" of the Pteraspidomorphi, or even the long-extinct conodonts, is still to be resolved. Even the very existence of the class Hyperoartia is disputed, with some analyses favoring a treatment of the "basal Hyperoartia" as a monophyletic lineage

Jamoytiiformes Jamoytiiformes is an extinct order of prehistoric jawless fish in the superclass Anaspidomorphi. Taxonomy Taxonomy is based on Mikko's Phylogeny Archive * Family † Achanarellidae Newman 2002 ** Genus †'' Achanarella'' Newman 2002 'Achanare ...

that may in fact be very close to the ancestral jawed vertebrates. The only hyperoartians surviving today are lampreys, classified in the

Petromyzontiformes Lampreys (sometimes inaccurately called lamprey eels) are an ancient extant lineage of jawless fish of the order Petromyzontiformes , placed in the superclass Cyclostomata. The adult lamprey may be characterized by a toothed, funnel-like su ...

. The discovery of the fossil '' Priscomyzon'' pushed back the oldest known occurrence of true lampreys to the Late Devonian. The evidence of phylogeny, however, suggests the lamprey lineage diverged much earlier from other vertebrates, rather than arising from among the "ostracoderms". The origin of Hyperoartia may therefore extend back to the early

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

, if not earlier. Mayomyzon NT small

Taxonomy and Phylogeny

Placed in this group are at present: Mikko's Phylogeny Archive, Nelson, Grande & Wilson 2016 and van der Laan 2018. * Clade Hyperoartia Müller 1844 ** Family † Hardistiellidae Halstead, 1993 ** Family † Mayomyzonidae Bardack, 1971 ** Family † Pipisciidae Halstead, 1993 ** Genus †'' Mesomyzon'' Chang, Zhang & Miao 2006 ** Genus †'' Priscomyzon'' Gess, Coates & Rubidge 2006 ** Order

(Lampreys) *** Family

Geotriidae ''Geotria'' is the only genus in the lamprey family Geotriidae. It has 2 known species: '' Geotria australis'' (pouched lamprey) and '' Geotria macrostoma'' (Argentinian lamprey). References Lampreys Taxa named by John Edward Gray Fis ...

(pouched lamprey) *** Family

Mordaciidae ''Mordacia'' is the sole genus of the family Mordaciidae, also known as the southern topeyed lampreys. Species There are currently three recognized species in this genus: * '' Mordacia lapicida'' ( J. E. Gray, 1851) (Chilean lamprey) * '' Mordaci ...

(southern topeyed lampreys) *** Family

Petromyzontidae The northern lampreys (Petromyzontidae) are a family of lampreys. Northern lampreys have the highest number of chromosomes (164–174) among vertebrates. Genera * '' Caspiomyzon'' * '' Entosphenus'' * ''Eudontomyzon'' * ''Ichthyomyzon'' * ''La ...

Risso, 1827 (Northern lampreys)

References

Fish classes {{jawless-fish-stub