section_path: Abstract
section_name: Abstract
paragraph_text: Vertebrates (/ ˈ v ɜːr t ə b r ɪ t s, - ˌ b r eɪ t s /) are deuterostomal animals with bony or cartilaginous axial endoskeleton — known as the vertebral column, spine or backbone — around and along the spinal cord, including all fish, amphibians, reptiles, birds and mammals. The vertebrates consist of all the taxa within the subphylum Vertebrata (/ ˌ v ɜːr t ə ˈ b r eɪ t ə /) and represent the overwhelming majority of the phylum Chordata, with currently about 69,963 species described.
  
  Vertebrates comprise groups such as the following infraphyla and classes:
  
  Extant vertebrates vary in body lengths ranging from the frog species Paedophryne amauensis, at as little as 7.7 mm (0.30 in), to the blue whale, at up to 33 m (108 ft). Vertebrates make up less than five percent of all described animal species; the rest are described as invertebrates, an informal polyphyletic group comprising all that lack vertebral columns, which include non-vertebrate chordates such as lancelets.
  
  The vertebrates traditionally include the hagfish, which do not have proper vertebrae due to their loss in evolution, though their closest living relatives, the lampreys, do. Hagfish do, however, possess a cranium. For this reason, the vertebrate subphylum is sometimes referred to as Craniata or "craniates" when discussing morphology. Molecular analysis since 1992 has suggested that hagfish are most closely related to lampreys, and so also are vertebrates in a monophyletic sense. Others consider them a sister group of vertebrates in the common taxon of Craniata.