How are Paracanthopterygii and Acanthopterygii related?

The Paracanthopterygii and Acanthopterygii are closely related groups of teleost fishes. Together, they are members of a larger clade known as the Acanthomorpha.1

Both superorders, along with the Scopelomorpha, are thought to have arisen from a common, early protacanthopterygian-like ancestor. These groups share specific evolutionary trends, including a tendency to develop spiny fin rays in the dorsal and anal fins and the development of a shelf of bone under the eye. Additionally, they exhibit a trend toward the forward movement of pelvic fins, which contributes to improved maneuverability.2

While the Paracanthopterygii are often characterized as a miscellaneous collection of fishes—most notably including cods—the Acanthopterygii represent a major radiation of modern spiny-rayed fishes, such as basses, perches, and mackerels. The Acanthopterygii are distinguished by their successful evolutionary radiation, which is largely attributed to the development of a mobile, protractile mouth.324