This study presents a cladistic analysis of the derivation of orthobothriotaxic patterns in scorpions. Included in this analysis are the original three orthobothriotaxic patterns defined by Vachon (1972, 1974), the pattern of the unique scorpion Pseudochactas ovchinnikovi Gromov, 1998, and two trichobothrial patterns of fossil scorpions, the Upper Carboniferous palaeopisthacanthids and the Lower Cretaceous archaeobuthids. An overview of all fossil scorpion material where trichobothria are reported is presented in detail. The approach used in this analysis is to model the existence of an individual trichobothrium, adopting the ‘absence of’, ‘petite size’ and ‘full size’ as incremental stages of a trichobothrium’s development. Of particular interest is the phylogenetic placement of Pseudochactas within Recent scorpions, for which the results of this study provide preliminary insight. Phylogenetic results of this analysis, based entirely on the derivation of orthobothriotaxic patterns, show that Archaeobuthus is the plesiomorphic sister group of all Recent scorpions, placed between the ancient palaeopisthacanthids and Recent scorpions. Within Recent scorpions, the clades ‘buthids + pseudochactids’ and ‘chaerilids + Type C’ are strongly endorsed by this analysis. Formal orthobothriotaxic types are defined for the palaeopisthacanthids (Type P), representing the earliest known complete fundamental trichobothrial pattern, and the pseudochactids (Type D), the fourth fundamental pattern for Recent scorpions.
Available at: http://works.bepress.com/victor_fet/8/