Palaeospondylus gunni Traquair
This tiny fish is found in reasonable numbers in Caithness at Achanarras and its equivalent locality Niand. The fish is extremely rare in the Sandwick Fish Bed on Orkney that is regarded equivalent in time and belonging to the same lake as Achanarras.
There is an impressive list of papers on this species and many theories are postulated about what group the fish should belong to.
In one of the most recent papers (Thomson, 2003) Palaeospondylus is presented as a larval dipnoan (Dipterus).