Evolutionary implications of hemipenial morphology in the terrestrial Australian elapid snakes

Venomous proteroglyphous or 'elapid' snakes are distributed across much of the tropical and subtropical world but are most diverse in Australia. Due to differing opinions of character weight and problems associated with high levels of homoplasy in traditionally used snake character systems, there is no well accepted hypothesis of phylogenetic relationships for the Australian elapids. Moreover, few or no synapomorphies have been identified to define many of the 20 currently recognized genera. As part of a re-evaluation of previous work, I have undertaken a survey of hemipenial morphology in this diverse radiation in a search for supraspecific synapomoiphies. Up to 14 aspects of hemipenial morphology were scored on 756 museum specimens and provide the basis for hemipenial descriptions of 64 species of Australian elapid. Morphology is highly conservative at generic levels and supportive of a number of previously suggested phyletic groups, but divergent between putative monophyletic lineages. Hemipenial morphology provides synapomorphies that define seven, and possibly eight, monophyletic groups at subgeneric, generic, and suprageneric levels: (1) Demansia, Oxyuranus, Pseudonaja, and Pseudechis each display unique hemipenial morphologies but share a number of character states. The following groups each share unique hemipenial types: (2) Simoselaps calonotus and the Simoselaps semifasciatus species group, (3) Vermicella and the Simoselaps bertholdi species group, (4) Cacophis and Furina, (5) Austrelaps, Echiopsis, Hoplocephalus, Notechis, and Tropidechis, (6) Drysdalia and Hemiaspis, (7) Rhinoplocephalus and Suta, and (8) Acanthophis and Denisonia. Higher level associations also are identified. The organs of Cacophis-Furina and Vermicella-Simoselaps bertholdi clades are very similar in shape and differ in only a single character. The Drysdalia-Hemiaspis and Rhinoplocephalus-Suta clades share a hemipenial shape and also differ in only a single character. Where sample sizes were sufficient for comparison, hemipenes displayed little or no intraspecific variation.