Phylogeny and Classification of the Superfamily Scorpionoidea Latreille 1802 (Chelicerata, Scorpiones): An Exemplar Approach

S. A. Stockwell (1989, "Revision of the Phylogeny and Higher Classification of Scorpions (Chelicerata)." Univ. of California, Berkeley) proposed a cladogram and revised classification for the superfamily Scorpionoidea Latreille 1802 (comprising the families Bothriuridae, Diplocentridae, Heteroscorpionidae, Ischnuridae, and Scorpionidae), based on 47 morphological characters and 35 supraspecific terminal taxa, representing genera whose monophyly was implicitly assumed. Given the widespread practice of defining scorpion genera on the basis of plesiomorphic character states, the assumption of monophyly implicit in supraspecific terminal taxa reduces confidence in Stockwell's cladistic findings and, consequently, his revised suprageneric classification. A re-investigation of scorpionoid phylogeny is presented here, based on 115 morphological characters (including the characters used by Stockwell) and 71 exemplar species. The criterion of "maximal morphological diversity" was employed for exemplar selection. This approach provides a stronger test of monophyly than random exemplar selection. Sixteen cladistic analyses were performed on the scorpionoid data matrix, which varied in the use of equal, successive, or implied weights and in the additive or nonadditive treatment of multistate characters. The preferred hypothesis, a single most parsimonious tree obtained by analysis with equal weights and 13 ordered multistate characters, yielded the scheme of relationships: (Bothriuridae ((Heteroscorpionidae Urodacinae) ((Hemiscorpiinae Ischnuridae) (Diplocentridae Scorpioninae)))). On the basis of these results, revisions are proposed to the existing suprageneric classification of the Scorpionoidea, including new diagnoses, new descriptions, and an illustrated key to the families and subfamilies. Familial status is provided for the scorpionid subfamilies Hemiscorpiinae and Urodacinae.