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Partial Paedomorphosis in the Mexican Stream Ambystomatids and the Taxonomic Status of the Genus Rhyacosiredon Dunn
Stephen M. Reilly and Ronald A. Brandon
Vol. 1994, No. 3 (Aug. 17, 1994), pp. 656-662
Stable URL: http://www.jstor.org/stable/1447181
Page Count: 7
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Diagnostic traits used to define the genus Rhyacosiredon are compared and contrasted to species of Ambystoma to reevaluate the validity of the genus Rhyacosiredon Dunn. Nearly all the characteristics on which the genus Rhyacosiredon was diagnosed (Dunn, 1928) are features of incompletely transformed salamanders in the Ambystoma tigrinum species group. A lack of a generic diagnosis and available genetic evidence indicate that the currently recognized genus Rhyacosiredon is polyphyletic, and generic status for these species is unwarranted. Species formerly placed in Rhyacosiredon exhibit a unique pattern of paedomorphosis involving the retention of "midmetamorphic" characteristics of the palate, hyobranchial apparatus, tooth crown morphology, and tongue. This peculiar form of paedomorphosis has independently evolved more than once in Mexican ambystomatids apparently as an adaptation to facilitate aquatic feeding in metamorphosed forms secondarily invading cold stream environments.