Macropalaeontology of the Trochocyathus-Trematotrochus band (Paleocene/Eocene boundary), Dilwyn Formation,Otway Basin,Victoria

Two new brachythoracids are described from the Taemas Limestone. Arenipiscis westolli gen. et sp. nov. possesses a skull-roof with deeply embayed posterior and elongate anterolateral margins, a large fused rostropineal plate, and orbits anteriorly placed and deeply notching the skull. The visceral skull-roof surface is developed with strong relief. The trunk-shield is poorly known, but the median dorsal plate probably had a prominent carinal process. Errolosteus goodradigbeensis gen. et sp. nov. is known only by an incomplete skull-roof, and anterior lateral and posterior ventrolateral plates. It has a highly distinctive ridged ornament. The affinities of these forms are considered in a discussion of brachythoracid interrelationships, and it is concluded that they are interchangeable on a cladogram with Buchanosteus. Other brachythoracids from the fauna, recently described by White, are considered, and it is suggested that Goodradigbeeon is phyletically primitive and Taemasosteus phyletically advanced relative to Buchanosteus. Schemes of brachythoracid interrelationships recently proposed by Denison and by Miles &; Dennis are compared, and a new scheme is proposed.