Zenaspidida

Zenaspida 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.

The head shield is dome-shaped and extremely large in comparison to the main body.

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.

[2][3] The cladogram below is adapted from a 2014 article by Scott and Wilson:[4] Spangenhelmaspis Parameteoraspis Balticaspis Trewinia Escuminaspis Levesquaspis Wladysagitta Glabrapelta Dentapelta Superciliaspis Machairaspis Scolenaspis Ukrainaspis Tegaspis Stensiopelta Diademaspis Zenaspis

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