Zenaspida

Zenaspidida

Zenaspidida

Extinct order of jawless vertebrates

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.

Quick Facts Scientific classification, Subgroups ...

Description

Cast of the zenaspidid Diademaspis mackenziensis. Early Devonian, Mackenzie Mountains, Northwest Territories (Canada). At the Royal Tyrrell Museum of Palaeontology.

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

The cladogram below is adapted from a 2014 article by Scott and Wilson:[4]

Zenaspidida

Spangenhelmaspis

Parameteoraspididae

Parameteoraspis

Balticaspis

Trewinia

Escuminaspis

Levesquaspis

Wladysagitta

Superciliaspididae

Glabrapelta

Dentapelta

Superciliaspis

Scolenaspididae

Machairaspis

Scolenaspis

Ukrainaspis

Zenaspididae

Tegaspis

Stensiopelta

Diademaspis

Zenaspis

References

  1. [1]
    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.
  2. [2]
    Voichyshyn, V. (2006). "New osteostracans from the Lower Devonian terrigenousdeposits of Podolia, Ukraine". Acta Palaeontologica Polonica. 51: 131–142 – via ResearchGate.
  3. [3]
    Voichyshyn, V. (2011). "THE EARLY DEVONIAN ARMOURED AGNATHANS OF PODOLIA, UKRAINE" (PDF). Palaeontologia Polonica. 66. Archived from the original (PDF) on February 14, 2023.
  4. [4]
    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.


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