Fish evolution: Ancient eyestalks

Achaonia is a new stem-group sarcopterygian (lobe-finned bony fish) from the Lower Devonian of China. It joins a select group of early fishes that possess a mixture of characters usually thought of as diagnostic of quite separate groups such as the extinct placoderms and acanthodians, as well as ray-finned and lobe-finned bony fishes. Unusually for a sarcopterygian, Achaonia has an eyestalk - generally considered to be a very primitive feature.

A primitive sarcopterygian fish with an eyestalk
MIN ZHU, XIAOBO YU, PER E. AHLBERG
Nature 410, 81-84 (1 March 2001)
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1 March 2001 table of contents