Abstract

The Onychodontiformes is a poorly known sarcopterygian fish group, with four genera currently described, predominantly from the Middle-Late Devonian. A new onychodont, Bukkanodus jesseni n. gen. and sp., from the Fairy Formation, Victoria, Australia, is of Early Devonian (mid-late Pragian) age, representing one of the oldest known occurrences of this group. Other Pragian onychodonts are represented by a single lower jaw from China, while older occurrences (Lochkovian) include a lower jaw also from China and isolated teeth from Nevada. The Australian material, though disarticulated, includes skull, jaw, and palatal and dental specimens. These specimens share characteristics with younger onychodont taxa, including a laterally compressed tooth whorl with main and accessory rows containing an equal number of teeth, an anteriorly arched shape of the premaxilla, a lateral rostral bone participating in the orbital margin, parietals separated in the midline by small bones, the insertion of the basisphenoid region of the braincase into a posterior area on the parasphenoid, and an ethmoidal sensory canal running along the dorsal margin of the premaxilla rather than through the bone. Bukkanodus jesseni differs from other onychodonts in the presence of a distinct vomer, coronoids with fang pairs, a restricted herringbone pattern of ribs on enamel ridges of teeth, and the presence of a cluster of large pores on certain skull and jaw bones. The course of the ethmoid sensory canal and this cluster of pores are plesiomorphic features for the Onychodontiformes, also occurring in primitive sarcopterygian taxa such as Youngolepis, Powichthys, and Kenichthys. The opening of this cluster on the internal surface of the premaxilla resembles the rostral organ of derived coelacanths.

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