Anaspida
| Anaspida Temporal range: 444–359Ma Early Silurian - Late Devonian |
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| Jamoytius kerwoodi | |
Scientific classification  |
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Craniata |
| Subphylum: | Vertebrata |
| Class: | †Anaspida Traquair, 1899 |
- For the reptiles, see Anapsida; for the crustaceans, see Anaspididae
Anaspida ("without shield") is an extinct group of primitive jawless vertebrates that lived during the Silurian and Devonian periods.[2] They are classically regarded as the ancestors of lampreys.[3] Anaspids were small marine agnathans that lacked heavy bony shield and paired fins, but have a striking highly hypocercal tail. They first appeared in the early Silurian, and flourished until the Late Devonian extinction,[4] where most species, save for lampreys, went extinct due to the environmental upheaval during that time.
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Anatomy [edit]
Unusually for an agnathan, anaspids did not possess a bony shield or armor. The head is instead covered in an array of smaller, weakly mineralized scales.[5] They have large, laterally placed eyes with no sclerotic ring, with the gills opened as a row of holes along either side of the animal, typically numbering anything from 6-15 pairs. The major synapomorphy for the anaspids is the large, tri-radiate spine behind the series of the gill openings.[1]
Phylogeny and taxonomy [edit]
| Anaspida |
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Notes [edit]
- ^ a b Janvier, Philippe (1997) Anaspida The Tree of Life Web Project.
- ^ Ahlberg, Per Erik (2001). Major events in early vertebrate evolution: palaeontology, phylogeny, genetics, and development. Washington, DC: Taylor & Francis. p. 188. ISBN 0-415-23370-4.
- ^ Patterson, Colin (1987). Molecules and morphology in evolution: conflict or compromise?. Cambridge, UK: Cambridge University Press. p. 142. ISBN 0-521-32271-5.
- ^ Hall, Brian Keith; Hanken, James (1993). The Skull. Chicago: University of Chicago Press. p. 131. ISBN 0-226-31568-1.
- ^ Janvier, Philippe (2003). Early Vertebrates. Oxford University Press. ISBN 978-0-19-852646-9.
External links [edit]
- "The Anaspida - unarmoured "ostracoderms"" (in en). Palaeos: Life Through Deep Time. Retrieved 2012-11-24.
- Monroe M. H. "Anaspida "no shield"" (in en). Australia: The Land Where Time Began. Retrieved 2012-11-24.
