Second tristichopterid (Sarcopterygii, Osteolepiformes) from the Upper Devonian of Canowindra, New South Wales, Australia, and phylogeny of the Tristichopteridae

ABSTRACT

A new tristichopterid, Cabonnichthys burnsi gen. et sp. nov. from the Upper Devonian Mandagery Sandstone near Canowindra, New South Wales, Australia, is the second tristichopterid to be described from this locality. The first, Mandageria fairfaxi, was interpreted as the sister group of the Laurussian taxon Eusthenodon. Cabonnichthys burnsi gen. et sp. nov. is similar to these two taxa in possessing a posterior supraorbital extending ventrally behind the orbit to exclude the postorbital from the orbital margin, a posteriorly positioned pineal surrounded by kite or teardrop shaped bones, and an enlarged fang-like tooth at the anterior end of the premaxillary tooth row. Cabonnichthys burnsi differs from Mandageria and Eusthenodon in retaining a contact between the intertemporal and posterior supraorbital, and in possessing “horn-like” processes on the postparietal shield that notch into the posterior margin of the postorbital. The Tristichopteridae is a clade characterized inter alia by the possession of postspiracular bones. A phylogenetic analysis of the Tristichopteridae yields the topology [Tristichopterus [Eusthenopteron [Jarvikina [Platycephalichthys [Cabonnichthys [Mandageria + Eusthenodon]]]]]]. This topology is consistent with the biostratigraphy of the group, and with a number of morphological trends including size increase and elaboration of the anterior dentition. It also suggests that the group has a northern origin and dispersed into Gondwana during the Upper Devonian.