Interrelationships of the elasmobranchs with a key to the order Galea. Bulletin of the AMNH ; v. 74, article 2. ; Interrelationships of elasmobranchs with key to Galea
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Text
Title:
Interrelationships of the elasmobranchs with a key to the order Galea. Bulletin of the AMNH ; v. 74, article 2. ; Interrelationships of elasmobranchs with key to Galea
Contributor:
White, Edith Grace, 1890-
[Author]
imprint:
New York : The American Museum of Natural History, 1937
Footnote:
Diese Datenquelle enthält auch Bestandsnachweise, die nicht zu einem Volltext führen.
Description:
p. 25-138, 51 p. of plates : ill. ; 25 cm. ; Includes bibliographical references (p. 132-138). ; "The results of this investigation tend to show that the characters of phylogenetic value are those not easily affected by the immediate environment or by the habits of a species. These characters have determined the main lines of development and are of value in determining groups of the grade of class, order, or suborder. They are deep-seated characters and include the vertebral structure, the basals of the paired fins and of the myxopterygia, the jaw attachment, and the rostral cartilages. The physiological characters are those which appear to have direct application to the environment or habits of the species. They cause wide variation within the groups determined by the phylogenetic characters and may be used in determining family, genus, or species relationships. These characters include the radials of the pectoral fin, the axial cartilages of the myxopterygia, the position of the dorsal fins, the teeth and denticles, the mouth and nostrils, the general body form, and all modifications of the skin such as folds, keels, pits, etc. The phylogenetic characters determine the lines of adaptive radiation and the physiological characters determine the adaptive radiation within the subgroups. The phylogenetic characters were laid down during the geological age of origin and when present today have been retained. The physiological characters may continue to vary at the present time. Certain physiological characters have become linked to the phylogenetic so consistently that linkage groups are suggested. Slight variations from the linkage may mean crossing over. The modern groups which were separated from the main stock more recently have proved to be more stable than those originating at an earlier time. Variation is, therefore, found in the more primitive groups and these may be supposed to be still in a varying or mutating condition. Certain species have been found to vary in characters otherwise typical of a group and ...