Devonian Fish

A fine specimen of the lung fish Dipterus from Achanarras, showing details of the lobe-fins. Image courtesy Nigel Trewin.
A fine specimen of the lung fish Dipterus from Achanarras, showing details of the lobe-fins. Image courtesy Nigel Trewin.

Fossils from the Devonian ‘Age of Fishes’ are found across Scotland, recording a time when life flourished in rivers and lakes. In the Devonian period, 417 to 354 million years ago, Scotland lay south of the equator in the southern arid belt and enjoyed a seasonal climate. Fish had evolved in the sea, but by Devonian times had invaded the rivers and lakes of the Old Red Sandstone continent, part of which was to become Scotland.

In the Midland Valley, some the best-preserved acanthodian (spiny-finned) fishes in the world are found in quarries near  Forfar. At Achanarras Quarry in Caithness, flagstones deposited in a deep lake have yielded the best preserved and most diverse assemblage of fish of that age in the world. Three new genera have been found and described in the last 15 years through the efforts of amateur collectors. The most common fossil is the lungfish Dipterus. These fish were preserved following mass mortalities.

Upper Devonian fossil fish were found at Dura Den in Fife in 1836 when quarrying revealed a sandstone bed covered with hundreds of fish including Holoptychius, a large predatory fish growing up to a metre long. The fish had been trapped in a pool that dried up, and sand covered and preserved the carcasses.

nigel_trewin_fossil_bookProf Nigel Trewin, University of Aberdeen says: Since 1970 I have been visiting Achanarras Quarry, searching for new elements of this superbly preserved Devonian fish fauna.

Tom Challands, University of Edinburgh says: My research interests concern evolution of the Dipnoi (lungfish), in particular, the evolution of sensory functions in this group and closely related organisms. I use microCT scanning techniques to probe the brain cavity and nerve and blood vessel canals in fossilised fish skulls which can then be used to test hypotheses of relationships between organisms during the vertebrate transition from water to land. This information also reveals exciting new data that can be used to gauge the evolution of senses (sight, smell, hearing) during this important period of vertebrate evolution.

Cast of the brain cavity of a Devonian fish from Scotland. Copyright Tom Challands / University of Edinburgh

Scotland has a rich diversity and history of palaeoichthyology – the study of fossil fishes. One of the best known Devonian fish from Scotland is a small lungfish called Dipterus valenciennesi which was first described in 1829. This animal was well-known to palaeontological titans such as Hugh Miller, Ramsay Traquair and Adam Sedgwick but modern techniques now allow us to look deeper into the hidden internal structures of this animal that these scientists could only have dreamed of in their time.

To this end, the current work being conducted on fossil fish from Scotland in universities and museums throughout the country shows that the legacy of Miller, Traquair and Sedgwick lives on. These fossils are of global importance as highlighted by the ground-breaking work that is currently being conducted on them in Scotland. Moreover, they can even be found in may of the pavements we walk on. The science of palaeontology is thriving in Scotland and we are certain to see more fantastic discoveries coming from Alba in the future.