The Heterotopic Shift in Developmental Patterns and Evolution of the Jaw in Vertebrates
What is evolutionary novelty? Generally, two distinct types of morphological changes are recognized in animal evolution. Firstly, the shape of a given structure can change to serve a new function, although the basic architecture of the derived structure is retained, and the homologous relationship is maintained through evolution. For example, the wing of the bat has been derived from the arm of the ancestral mammal, and all the anatomical components of the mammalian arm, such as the bones, muscles, and nerve branches, can be found in the bat wing, arranged in the same order and with the same topographical patterns. In other words, bat wings develop under the strong constraints that constitute the mammalian body plan. Wagner and Müller  have called such changes “adaptation” and regard them as not fundamentally new or innovative, but as evolutionary changes. Most evolutionary changes belong to this category, at least to the extent that specific fields of evolutionary biology, such as, comparative embryology and morphology, can establish.
KeywordsCrest Cell Homeobox Gene Mandibular Arch Turtle Shell Early Chick Embryo
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