A New Middle Devonian Arthrodire (Placoderm Fish) from the Broken River Area, Queensland

Abstract

Associated bones of the trunk-armour belonging to a large brachythoracid arthrodire are described as Confractamnis johnjelli n.gen. and n.sp. The specimen comes from strata of probable Eifelian age in the Broken River Group of Queensland. It shows a range of derived brachythoracid features including reduction of dermal ornament, and strong development of the dermal neck joint articulation. The posterior dorsolateral and posterior lateral plates of the trunk armour were high and narrow, and the anterior lateral plate had a distinctive narrow bilobed dorsal angle as indicated by the shape of its overlap area on the anterior dorsolateral plate. A provisional reconstruction suggests that the bones came from a large fish over 2 m in length. A cross section of the trunk armour is compared with the large arthrodire Taemasosteus from the Early Devonian of Burrinjuck, New South Wales. A possible close relative of this new taxon has been illustrated from the Early Devonian of Morocco, supporting other indications of resemblance in placoderm fish assemblages between these regions of east and north Gondwana during the Early-Middle Devonian.