Here we continue my coverage of the many jawless fish seen in the fossil record. This time we got another very small monotypic taxon whose taxonomy is just slightly contentious. Last time I mentioned this but basically in terms of jawless fish there are two branches. One that leads to jawed fish and second the one we shall be covering first that leads to modern jawless fish. Ironically despite still being alive this lineage is far more contentious likely due to how the vast majority of this clade do not have hard bony armor

Jamoytius kerwoodi is the only member of the order Jamoytiiformes. Though this itself is a bit contentious as sometimes it is grouped alongside the Anaspida into the superclass Anaspidomorphi, but this may in fact be a paraphyletic collection of early members of the lineage excluding conodonts and Cyclostomi (the clade that includes hagfish and lampreys). Regardless of where it fits this animal seems to represent the basal condition of the clade even if it is not technically the oldest member of the clade in terms of it's time.

On the subject of the animal itself it lived from the Rhuddanian stage of the early Silurian 443.8 mya and lasted until the Homerian stage of the middle Silurian around 427.4 mya in what is now called the Patrick Burn Formation of Lesmahagow, Scotland. It has been often reconstructed with paired fins but these were mistakes stemming from deformation originating post death. It had small weakly mineralized scales that would not have been easily visible in life.
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