Biology:Zenaspida
| Zenaspida | |
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| Fossil of Zenaspis powriei | |
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| Order: | Zenaspidida Stensiö, 1958 sensu Sansom, 2009
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Zenaspidida | |
Zenaspida is an extinct order of jawless fish.[1] They possessed a distinct headshield, which varied in width to length ratio by species.
Description
The head shield is dome-shaped and extremely large in comparison to the main body. The abdominal section of this shield has a less developed median dorsal crest. As a rule for this order, the nasohypophysial opening is larger than the nasal division. The pinneal plate seen in other Osteostraci is barely developed or completely absent. The median dorsal field is notably broad, and the lateral fields are widened in the posterior, but reach back no further than the proximal section of the dorsal surface of the cornual processes. The ornamentation on the head shield can have singular, large tubercles, or groups of tubercles which range in size. This is often used to speciate.[2][3]
References
- ↑ Scott, Bradley R.; Wilson, Mark V. H. (2013). "A new species of osteostracan from the Lochkovian (Early Devonian) of the Mackenzie Mountains, with comments on body size, growth, and geographic distribution in the genus Machairaspis". Canadian Journal of Earth Sciences 50 (2): 127–134. doi:10.1139/cjes-2012-0100.
- ↑ Voichyshyn, Victor (2006). "New osteostracans from the Lower Devonian terrigenousdeposits of Podolia, Ukraine". Acta Palaeontologica Polonica 51: 131-142. https://www.researchgate.net/publication/213775597_New_osteostracans_from_the_Lower_Devonian_terrigenous_deposits_of_Podolia_Ukraine.
- ↑ Voichyshyn, Victor (2011). "THE EARLY DEVONIAN ARMOURED AGNATHANS OF PODOLIA, UKRAINE". Palaeontologia Polonica 66. http://www.palaeontologia.pan.pl/PP66/PP66.pdf.
External links
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Wikidata ☰ Q21292264 entry
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