Dipterus valenciennesi Sedgwick & Murchison

Complete specimen in lateral view showing well the paired fins. This specimen shows some cosmine on part of the scales on the belly, and a patch of cosmine on the opercular and the plate below the lower jaw. From Achanarras, Caithness.

Close-up of above fish showing the tail and the fins. af: anal fin, c: cosmine, df1: anterior dorsal fin, df2: posterior dorsal fin, pvf: pelvic fin. Note that the scales on the belly have cosmine and some of the scales on the fins also.
At the start of the 19th century the lungfish Dipterus was one of the first fish described in many papers. It has peculiar tooth plates and a strange lower jaw. Together with this, and the fact that there are still lungfish living today, it makes this a very interesting fish. On Orkney articulated specimens can be found in the Sandwick Fish Bed and disarticulated specimens almost everywhere. In the Eday Subgroup Dipterus is “replaced” by Pentlandia macroptera.
Most likely for protection against predators, and the harsh environment the fish has cosmine on the scales and headplates. Juvenile fish however had no cosmine and the scales and headplates are not shiny. The plates on top of the head, the cranial shield, are very simple in juvenile fish but become more complex in bigger specimen. In adult specimens the cranial shield as well as the other plates and scales are cosmine covered.
Two heads from the Sandwick Fishbed. CS: cranial shield, E: eye, O: opercular
Cranial shields of Dipterus with full cosmine and partial cosmine in outside and inside view.
Scales with and without cosmine.
Some old historic reconstructions:
Drawing of specimen (after Miller, 1841, 1849). (after Miller, 1849).