Acanthodes

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Acanthodes was an extinct, spiny fish that lived from about 359 to 284 million years ago. Fossils have been found in Europe, North America, and Asia, making it one of the youngest known acanthodians.

Size and body: Acanthodes varied in size from about 15 cm to at least 80 cm long. It had an elongated body with a pair of pectoral fins, a single dorsal fin far back on the body, a long ventral/pelvic fin, and an anal fin on the underside. Spines protected the front edges of these fins. The body was covered in scales, and the backbone was usually not ossified (not fully bony).

Teeth and feeding: Acanthodes had no teeth and long gill rakers, so it is thought to have fed by filtering plankton from the water (suspension feeding).

Eyes and vision: A specimen of Acanthodes bridgei preserved eye tissue showing both rod and cone cells, suggesting it could see color.

Habitat: These fish lived in freshwater lakes and in saline lagoons.

Diet and ecology: Acanthodes bronni, from freshwater lakes in early Permian Germany, was prey for temnospondyl amphibians like Archegosaurus and Glanochthon. The fish could open its jaws wide, possibly rotating them outward to increase its gape for catching plankton.

Classification: The classification of acanthodians has been debated, but by the 2010s researchers concluded that acanthodians are a paraphyletic group of stem-air chondrichthyans (early relatives of sharks and rays). Within this group, Acanthodes is placed in the order Acanthodiformes, though that group is also considered paraphyletic. Some species, such as Acanthodes tholeyi from Early Permian Germany, have been reassigned to other genera (for example, Westrichus).