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Evolution of scorpion orthobothriotaxy – a cladistic approach.

Author(s): Soleglad, M.E. | Fet, V.

Journal: Euscorpius
ISSN 1536-9307

Issue: 01;
Start page: 1;
Date: 2001;
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Keywords: scorpions | trichobothria | phylogeny | Pseudochactidae

This study presents a cladistic analysis of the derivation of orthobothriotaxic patterns in scorpions. Included in thisanalysis are the original three orthobothriotaxic patterns defined by Vachon (1972, 1974), the pattern of the uniquescorpion Pseudochactas ovchinnikovi Gromov, 1998, and two trichobothrial patterns of fossil scorpions, the UpperCarboniferous palaeopisthacanthids and the Lower Cretaceous archaeobuthids. An overview of all fossil scorpionmaterial where trichobothria are reported is presented in detail. The approach used in this analysis is to model theexistence of an individual trichobothrium, adopting the ‘absence of’, ‘petite size’ and ‘full size’ as incrementalstages of a trichobothrium’s development. Of particular interest is the phylogenetic placement of Pseudochactaswithin Recent scorpions, for which the results of this study provide preliminary insight. Phylogenetic results of thisanalysis, based entirely on the derivation of orthobothriotaxic patterns, show that Archaeobuthus is the plesiomorphicsister 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 bythis analysis. Formal orthobothriotaxic types are defined for the palaeopisthacanthids (Type P), representing the earliestknown complete fundamental trichobothrial pattern, and the pseudochactids (Type D), the fourth fundamentalpattern for Recent scorpions.
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