The enigmatic vertebrate Palaeospondylus gunni, from the Middle Devonian of Scotland, has been described as a larval lungfish (dipnoan), most probably of the genus Dipterus. Metamorphosis was said to account for the extreme morphological differences between the two taxa, with distinct size differences between them. However, this is contradicted by a newly discovered specimen of Dipterus, the smallest known. This specimen falls within the size range of the largest P. gunni specimens, and possesses well-developed tooth plates, a feature lacking in all specimens of P. gunni. Juvenile dipnoans of other species are known, which also show that the tooth plates develop in the smallest observable individuals. The occurrence of P. gunni in the Sandwick fish bed in Orkney is confirmed, and it is confirmed too that it does not occur at Baligill, Sutherland.