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      Lift based mechanisms for swimming in eurypterids and portunid crabs

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          Abstract

          The striking morphological similarity that exists between appendages of the extant portunid crabs, such as Callinectes sapidus, and those of the extinet eurypterids has long been noted. The fifth pair of pereiopods in blue crags and other portunids are modified to form the broad, flat, highly mobile ‘swim paddles.’ A nearly identical modification is seen in the sixth pair of prosomal appendages of many eurypterids. The similarities are due to convergence and not to shared descent.

          The kinetics of blue crab swimming were studied using high speed films. The animals are capable of slow upwards locomotion (‘hovering’) and rapid sideways swimming. The blue crab paddles apparently act as reciprocating hydrofoils, employing well-understood principles of lift and thrust generation to overcome the animal's weight and drag. Experimental studies indicated that the paddles are capable of producing appreciable amounts of lift. Drag on the body and paddles was also determined. Resxults are similar to those obtained in previous studies of bird and insect flight.

          The physical principles employed to study blue crab swimming can be applied to the study of eurypterid locomotion. The eurypterid paddles may have functioned as hydrofoils, producing lift and thrust on forestroke and backstroke. Eurypterids were probably highly agile and manoueverable swimmers, capable of hovering and of high speed swimming. This model predicts observed morphological correlates. Predicted morphological correlates of earlier models (often based on analogies with Limulus) were not found.

          The observed convergence between eurypterids and blue crabs may have resulted from similar functional constraints and parallel phylogenetic histories.

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          Most cited references25

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          Hydromechanics of Aquatic Animal Propulsion

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            Form and Function in Fish Swimming

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              Form and function: structural analysis in evolutionary morphology

              A theoretical approach to the analysis of historical factors (Raup 1972) in evolutionary morphology is presented which addresses transformational hypotheses about structural systems. This (structural) approach to testing historical hypotheses about phylogenetic constraints on form and function and structural and functional versatility involves (1) the reconstruction of nested sets of structural features in monophyletic taxa, (2) the use of general or emergent organizational properties of structural and functional systems (as opposed to uniquely derived morphological features), and (3) the comparative examination of the consequences for structural and functional diversity of these general features in related monophyletic taxa.
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                Author and article information

                Journal
                applab
                Transactions of the Royal Society of Edinburgh: Earth Sciences
                Transactions of the Royal Society of Edinburgh: Earth Sciences
                Cambridge University Press (CUP)
                0263-5933
                1473-7116
                1985
                November 2011
                : 76
                : 2-3
                : 325-337
                Article
                10.1017/S0263593300010543
                89b6eebb-701f-477d-8a32-b8ac8094478a
                © 1985
                History

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