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Feeding Specializations and the Classification of Terrestrial Salamanders
Philip J. Regal
Vol. 20, No. 3 (Sep., 1966), pp. 392-407
Published by: Society for the Study of Evolution
Stable URL: http://www.jstor.org/stable/2406638
Page Count: 16
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Consideration of adaptations to feeding in terrestrial situations indicates co-selection for a tongue that may be darted out of the mouth, and posterior migrations of the palatal teeth which bring a greater portion of the roof of the mouth into use in the manipulation of food. Progressive changes in tongue structure in various salamander groups are all essentially parallel and selection for extensibility involves primarily quantitative changes in a basic pattern of organization. Selection for the posterior movement of palatal teeth can be shown to have taken place in two quite different ways. The condition represented by the Salamandridae takes place by the simple migration of the larval palatal arch of teeth onto the parasphenoid so that the adult condition is roughly parallel to the larval. In other terrestrial salamanders the trend is for a more accelerated posterior migration of the medial portion of the vomer to bring the palatal dentition at right angles to the larval position (Ambystomatidae) and finally, through nearly a 180-degree rotation (Plethodontidae) into a position which had been considered the equivalent of the salamandrid condition. It is possible that evolution of terrestrial characters has been quite independent in various lines, but on the basis of general similarity, the larger group probably represents an assemblage of closely related families, the Ambystomatoidea. The condition of the palate is probably a condition which has arisen only once in this group. Other characters strongly suggest independent terrestrial evolution in its three lines and close morphological similarity reflects very close relationship at a lower level of organization. Rhyacotriton is a form which could be classified with a group of hypothetical early adaptive types in the Ambystomatoidea. It is suggestive that the families are related at a point subsequent to occupation of semiterrestrial adaptive zones. A classification of the Caudata is proposed which differs significantly in premise and organization from that now accepted. Groupings are based on probable relationships rather than the hypothetical splitting off of one group from another. Groups of problematical relationships, such as the Proteidae, Sirenidae, and Amphiumidae are isolated rather than pigeonholed. Aquatic forms which demonstrate clear relationships are afforded only subfamilial status (Cryptobranchus and Megalobatrachus, and the newts, which are certainly not aquatic in the same sense). Plethodontids related to Desmognathus are retained as only a subfamily. It is acknowledged that the remainder of the Plethodontidae are quite closely related to one another. Exception is taken to the attempted demonstrations of earlier workers that the free-tongues of the eastern United States represent ancestral stock while the Neotropical group is a derivative of more advanced plethodontids. Free-tongued genera thus are considered to represent radiation into an adaptive zone open primarily to more advanced plethodontids with the eastern section involved in a secondary, aquatic trend resulting in what is only a superficial similarity to newts.
Evolution © 1966 Society for the Study of Evolution