Description
About Cheiracanthus murchisoni Cheiracanthidae
Physical Description
Cheiracanthus murchisoni is the largest of the acanthodians from the Orcandian basin. Its a large fish ranging from 60 mm to about 250 mm. C. murchisoni on first impression looks like a very large Mesacanthus. Like its smaller cousin it had only one dorsal fin spine. But it differs as this spine was more to the middle of the body compared dorsal fin of the Mesacanthus which is situated more to the rear of the fish. The name Cheiracanthus comes from greek, meaning hand spine (cheira-canthus)
Age and Distribution
Cheiracanthus murchisoni is from the Middle Devonian of Scotland. This fish lived approximately 385 million years ago. At the time this area of Scotland was part of the Orcadian Basin, which was a huge complex of lakes that stretched for hundreds of miles. During this period plants started to rapidly colonize the land and fishes dominated nearly every niche of seas and lakes, hence why this period is also known as the “Age of Fishes”. Cheiracanthus murchisoni co-inhabited the lake with other fishes like the acanthodian Mesacanthus and Diplacanthus crassismus, the osteolepids Gyroptychius, Osteolepis, and Thursius, the porolepid Glyptolepis, the lungfish Dipterus, the enigmatic Palaeospondylus gunni and the placoderms Dickosteus, Coccosteus, Pterichtyodes, Rhamphodopsis and Homostius.
About the Acanthodii Cheiracanthidae
Evolutionary Significance
The Acanthodii are among the earliest jawed vertebrates known in the fossil record. The oldest acanthodians found are from the Lower-Silurian. This group disappears from the known fossil record at the Permian-Triassic extinction event, long after they had already dwindled in diversity.
Taxonomy
Cheiracanthus murchisoni belongs to the Cheiracanthidae which is a subclass of the Acanthodii (‘spiny sharks’, which means that, though they also had a skin cover of denticles, it is uncertain that they are closely related to sharks). Other Cheiracanthidae from Middle-Devonian of Scotland are: Cheiracanthus latus.
