A primitive actinopterygian neurocranium from the Early Devonian of southeastern Australia

ABSTRACT

A well-preserved neurocranium with attached partial skull roof is described from the Early Devonian Taemas Formation at Wee Jasper, southern New South Wales, Australia. The dermal ornament, skull roof pattern, and general proportion and structure of the endocranium are typically actinopterygian and the specimen is tentatively assigned to the actinopterygian genus Ligulalepsis. Other features more closely resemble some other groups, such as sarcopterygians (widely-spaced orbital walls, and short, broad telencephalon cavity), acanthodians (position of hyo-mandibular facet), and placoderms (many similarities including position of foramina for oculomotor, profundus, and trigeminal nerves, pituitary vein, and ophthalmic and orbital arteries in and around the orbit). This specimen is the first early osteichthyan to demonstrate the presence of an eyestalk, previously known only in placoderms and chondrichthyans. The unusual mix of characters and presence of an eyestalk provide new insights into primitive osteichthyan anatomy.