A tiny fossil fish found only in rocks of Middle Devonian age within a small geographic region of Caithness, Scotland, and principally at one site, Achanaras Quarry, where it is surprisingly abundant. One of the most enigmatic of all fossil fishes, Palaeospondylus gunni was discovered in 1890 by Marcus and John Gunn and described by Ramsay Traquair. Its original environment was a large, deep, freshwater lake system with a broad diversity of fishes. Unusually for a tiny fish, Palaeospondylus is typically found in sediments associated with the deepest part of the lake.