Zenaspidida is an extinct order of osteostracans, a group of jawless stem-gnathostomes.[1] They possessed a distinct headshield, which varied in width to length ratio by species.
| Zenaspidida | |
|---|---|
| |
| Fossil of Zenaspis powriei | |
Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | †Osteostraci |
| Order: | †Zenaspidida Stensiö, 1958 |
| Subgroups | |
| Synonyms | |
|
Zenaspida | |
Description
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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 pineal plate seen in other osteostracans 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]
Classification
editThe cladogram below is adapted from a 2014 article by Scott and Wilson:[4]
References
edit- ^ Scott, B. R.; Wilson, M. 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, V. (2006). "New osteostracans from the Lower Devonian terrigenousdeposits of Podolia, Ukraine". Acta Palaeontologica Polonica. 51: 131–142 – via ResearchGate.
- ^ Voichyshyn, V. (2011). "THE EARLY DEVONIAN ARMOURED AGNATHANS OF PODOLIA, UKRAINE" (PDF). Palaeontologia Polonica. 66. Archived from the original (PDF) on February 14, 2023.
- ^ Scott, B. R.; Wilson, M. V. H. (2015). "The Superciliaspididae, a new family of Early Devonian Osteostraci (jawless vertebrates) from northern Canada, with two new genera and three new species". Journal of Systematic Palaeontology. 13 (3): 167–187. doi:10.1080/14772019.2013.863809.
External links
edit- "Zenaspidida". The Encyclopedia of Life.
- "Agnatha". paleofile.com. Archived from the original on April 10, 2021.
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