genus of enigmatic fossil vertebrates that were very fishlike in appearance but of uncertain relationships. Palaeospondylus, from the Middle Devonian epoch (398 million to 385 million years ago), has been found in the Old Red Sandstone rocks in the region of Achannaras, Scot. Hundreds of specimens are known, yet the position of this genus in relation to other fishlike vertebrates is still poorly understood. Palaeospondylus was about 5 cm (about 2 inches) long. Unlike most of the contemporary forms of the Middle Devonian, the skeleton of Palaeospondylus was very well ossified, and no dermal armour was present, a feature prominent among the placoderms (placoderm). A well-developed caudal, or tail, fin was present.