Anaspida

Updated on Oct 03, 2024

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Kingdom Animalia Subphylum Vertebrata		Phylum Chordata Rank Superorder

Class †AnaspidaTraquair, 1899 Similar Osteostraci, Thelodonti, Galeaspida, Pteraspidomorphi, Heterostraci

Anaspida ("without shield") is an extinct group of primitive jawless vertebrates that lived primarily during the Silurian period, and became extinct soon after the start of the Devonian. They were once classically regarded as the ancestors of lampreys. Anaspids were small marine agnathans that lacked a heavy bony shield and paired fins, but have a striking highly hypocercal tail. They first appeared in the early Silurian, and flourished until the early Devonian, where they then disappear from the fossil record.

Anatomy

Anaspida httpsuploadwikimediaorgwikipediacommonsthu

Compared to other prehistoric agnathan groups, such as the Heterostraci and Osteostraci, anaspids did not possess a bony shield or armor, hence their name. The anaspid head and body are instead covered in an array of small, weakly mineralized scales, with a row of massive scutes running down the back, and, at least confirmed among the birkeniids, the body was covered in rows of tile-like scales made of aspidine, an acellular bony tissue. Anaspids all had prominent, laterally placed eyes with no sclerotic ring, with the gills opened as a row of holes along either side of the animal, typically numbering anywhere from 6-15 pairs. The major synapomorphy for the anaspids is the large, tri-radiate spine behind the series of the gill openings.

Taxonomy

Anaspida Palaeos Vertebrates Anaspida Anaspida

Now that Jamoytius and its close cohorts, i.e., Euphanerops, have been moved to Jamoytiiformes, Class Anaspida now consists of two orders, the monogeneric Lasaniida, which contains the genus Lasanius and represents a basal anaspid group, and Birkeniida, which contains all other recognized anaspid taxa. Birkeniida is further divided into several families, including Birkeniidae, Pterygolepididae, Rhyncholepididae and Pharyngolepididae, which contain those taxa known from whole body fossils (in addition to several taxa known only from scales) and the family Septentrioniidae, whose subtaxa are known exclusively from scales. Two recently described genera, Kerreralepis and Cowielepis, are considered to be Birkeniida incertae sedis.

A newer taxonomy based on the work of Nelson, Grande and Wilson 2016 and van der Laan 2016.

Super Class †Anaspidomorphi

Order †Euphanerida

Family †Euphaneropidae Woodward 1900

Genus †Ciderius van der Brugghen 2015

Genus †Cornovichthys Newman & Trewin 2001

Genus †Euphanerops Woodward 1900 [Legendrelepis Arsenault & Janvier 1991]

Order †Jamoytiiformes Halstead-Tarlo 1967

Family †Achanarellidae Newman 2002

Genus †Achanarella Newman 2002 [Achanarella Rowlands (nomen nudum)]

Family †Jamoytiidae White 1946

Genus †Jamoytius White 1946

Class †Anaspida Janvier 1996 non Williston 1917

Order †Endeiolepidiformes Berg 1940

Family †Endeiolepididae Stensiö 1939 corrig.

Genus †Endeiolepis Stensiö 1939

Order †Birkeniiformes Berg 1940

Genus †Cowielepis Blom 2008

Genus †Hoburgilepis Blom, Märss & Miller 2002

Genus †Kerreralepis Blom 2012

Genus †Maurylepis Blom, Märss & Miller 2002

Genus †Rytidolepis Pander 1856

Genus †Schidiosteus Pander 1856

Genus †Silmalepis Blom, Märss & Miller 2002

Genus †Vesikulepis Blom, Märss & Miller 2002

Family †Pharyngolepididae Kiær 1924 corrig.

Genus †Pharyngolepis Kiaer 1911

Family †Pterygolepididae Obručhev 1964 corrig.

Genus †Pterygolepis Cossmann 1920 [Pterolepis Kiaer 1911 non Rambur 1838 non De Candolle ex Miquel 1840; Pterolepidops Fowler 1947]

Family †Rhyncholepididae Kiær 1924 corrig.

Genus †Rhyncholepis Kiær 1911 non Miquel 1843 non Nuttall 1841

Family †Tahulalepididae Blom, Märss & Miller 2002

Genus †Tahulalepis Blom, Märss & Miller 2002

Genus †Trimpleylepis Miller, Märss & Blom 2004

Family †Lasaniidae Goodrich 1909

Genus †Lasanius Traquair 1898

Family †Ramsaasalepididae Blom, Märss & Miller 2003

Genus †Ramsaasalepis Blom, Märss & Miller 2003

Family †Birkeniidae Traquair 1899

Genus ?†Vilkitskilepis Märss 2002

Genus †Ctenopleuron Matthew 1907

Genus †Saarolepis Robertson 1945 [Anaspis Robertson 1941 non Geoffroy 1762 non Thomson 1893]

Genus †Birkenia Traquair 1898

Family †Septentrioniidae Blom, Märss & Miller 2002

Genus †Liivilepis Blom, Märss & Miller 2002

Genus †Manbrookia Blom, Märss & Miller 2002

Genus †Ruhnulepis Blom, Märss & Miller 2002

Genus †Spokoinolepis Blom, Märss & Miller 2002

Genus †Septentrionia Blom, Märss & Miller 2002

Anaspida Anaspida Wikipedia la enciclopedia libre

References

Anaspida Wikipedia

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Contents

Anatomy

Taxonomy

References