A NEW PLOURDOSTEID ARTHRODIRE FROM THE UPPER DEVONIAN GOGO FORMATION OF WESTERN-AUSTRALIA

A new plourdosteid arthrodire, Mcnamaraspis kaprios gen. et sp. nov., is described from the Late Devonian (Frasnian) Gogo Formation of Weste rn Australia. Mcnamaraspis is characterized by its very short spinal p late, larger pectoral fenestra and inferognathal with several distinct trenchant cusps. The anterior surface of the nasal capsule is covered by a hemispherical bone not previously recorded in placoderms. This i s interpreted as an ossified annular cartilage, and, together with the interpretation of the suborbitalis muscle being present in arthrodire s, supports the hypothesis that placoderms are more closely related to chondrichthyans than to osteichthyans. Mcnamaraspis is placed as the sister taxon to Torosteus in the family Plourdosteidae. The Plourdoste idae is redefined. Interrelationships of plourdosteids and relationshi ps to other eubrachythoracid arthrodires are discussed.