Trisha Shetty

Anaspida

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Kingdom  Animalia
Subphylum  Vertebrata
Phylum  Chordata
Rank  Superorder
Anaspida Anaspida
Class  †Anaspida Traquair, 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.

Contents

Anaspida FIGURE 1

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.

Anaspida Anaspida Wikipedia
  • Super ClassAnaspidomorphi
  • Order †Euphanerida
  • FamilyEuphaneropidae 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
  • FamilyAchanarellidae Newman 2002
  • Genus †Achanarella Newman 2002 [Achanarella Rowlands (nomen nudum)]
  • FamilyJamoytiidae White 1946
  • Genus †Jamoytius White 1946
  • ClassAnaspida Janvier 1996 non Williston 1917
  • OrderEndeiolepidiformes Berg 1940
  • FamilyEndeiolepididae Stensiö 1939 corrig.
  • Genus †Endeiolepis Stensiö 1939
  • OrderBirkeniiformes 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
  • FamilyPharyngolepididae Kiær 1924 corrig.
  • Genus †Pharyngolepis Kiaer 1911
  • FamilyPterygolepididae Obručhev 1964 corrig.
  • Genus †Pterygolepis Cossmann 1920 [Pterolepis Kiaer 1911 non Rambur 1838 non De Candolle ex Miquel 1840; Pterolepidops Fowler 1947]
  • FamilyRhyncholepididae Kiær 1924 corrig.
  • Genus †Rhyncholepis Kiær 1911 non Miquel 1843 non Nuttall 1841
  • FamilyTahulalepididae Blom, Märss & Miller 2002
  • Genus †Tahulalepis Blom, Märss & Miller 2002
  • Genus †Trimpleylepis Miller, Märss & Blom 2004
  • FamilyLasaniidae Goodrich 1909
  • Genus †Lasanius Traquair 1898
  • FamilyRamsaasalepididae Blom, Märss & Miller 2003
  • Genus †Ramsaasalepis Blom, Märss & Miller 2003
  • FamilyBirkeniidae 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
  • FamilySeptentrioniidae 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
    Anaspida Anaspida
    Anaspida Palaeos Vertebrates Anaspida Anaspida

    References

    Anaspida Wikipedia


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