The crossopterygians, lobbed finned fishes, played an important role in the Orcadian Basin and in the evolution of man.
In the lake, these fast swimming fishes with their strong teeth were the top predators. They evolved to form the first land animals during the Upper Devonian.
The similarity of the skull and dermal skull bones and the bony structure supporting the paired fins are striking when compared with the first land animals.
This group of fishes was thought to be extinct. In 1938 a strange fish was found in South Africa by Mrs. Latimer, brought to her by a local fisher. Later the fish was identified as a Coelacanth, a living member of the Crossopterygians. Fossil Coelacanths are known from Germany, found in the limestones from the Jurassic Period. This discovery had an impact on the scientific community comparable with the finding of the tomb of Tutankhamon.
The coelacanths are a group of fishes belonging to the crossopterygians. The crossopterigyans found in the sediments of Orkney can be divided in the porolepiforms and the osteolepiforms.
The osteolepiforms from the Middle Devonian of Orkney all (except Tristichopterus) have a hard shiny layer on their bony scales, the cosmine.
The porolepiforms are generally larger than the osteolepiforms and had scales ornamented with tubercles and ridges.
There is no doubt anymore that the first land animals must have evolved from the crossopterygians. New crossopterygian material will certainly make the picture of this step from water to land more complete.