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OriginsThe Search for Our Prehistoric Past$
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Frank H. T. Rhodes

Print publication date: 2016

Print ISBN-13: 9781501702440

Published to Cornell Scholarship Online: January 2017

DOI: 10.7591/cornell/9781501702440.001.0001

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Bone, Scales, and Fins: The Early Vertebrates

Bone, Scales, and Fins: The Early Vertebrates

(p.91) 6 Bone, Scales, and Fins: The Early Vertebrates

Frank H. T. Rhodes

Cornell University Press

This chapter examines the early vertebrates. The major group to which vertebrates are assigned—phylum Chordata—includes two small groups (the tunicates and the cephalochordates) and one large group: the vertebrates (or Craniata). Most chordates are bilaterally symmetrical, with complete, relatively complex digestive tracts. There are nine major groups of vertebrates, five of them “fishes” and four of them tetrapods. Although chordates constitute only some three percent of all living species, they are widely distributed, marvelously adapted, numerically abundant, and strikingly successful. All share a few distinguishing characteristics for at least part of their development: a single hollow nerve cord, which is differentiated in vertebrates into the brain and spinal cord; a notochord, a flexible rodlike axis, running underneath and supporting the nerve cord; pharyngeal gill slits; a tail extending beyond the anus; and segmentation, reflected in the muscles and the vertebral column.

Keywords:   early vertebrates, chordates, bones, jawless fish, acanthodians, fishes, placoderms, sharks, rays, bony fishes

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