1) The chord and subsequently the spine are the basis of the internal skeleton of animals.
2) The emergence of the internal skeleton allowed the creation of a new type of body support and a new way of attaching muscles.
3) The appearance of the internal skeleton provided chordates with an increase in the size of the body, high differentiation of its sections and, above all, the musculoskeletal system.
4) As a result of these changes, chordates turned out to be at a much higher level of organization than invertebrates. Therefore, their appearance can be considered an aromorphosis
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