Primitive bony fishes, with especial reference to Cheirolepis and palaeonisciform actinopterygians

The relationships of the Devonian palaeonisciform fish Cheirolepis are examined and the early evolutionary trends within the Actinopterygii and the Osteichthyes are considered. Cherrolepts is the most primitive known actinopterygian. The contemporary stegotrachelid palaeonisciforms are more advanced in their cranial and locomotor anatomy. The general directions of these advances are similar to those subsequently displayed by later palaeonisciforms over the stegotrachelids themselves. Cheiroolepis, furthermore, possesses many characters which can be logically interpreted as primitive for the Osteichthyes by extrapolation of trends in actinopterygian and sarcopterygian lineages. It is the most primitive known osteichthyan. The Osteichthyes are considered to have arisen from a micromerically-scaled acanthodian or acanthodian-like ancescor at the end of the Silurian period.