page_title: Evolutionary taxonomy
section_title: The Tree of Life
hierarchical_section_title: Evolutionary taxonomy / The Tree of Life
caption_attribution_description: English: Evolution of Vertebrate from the Cambrium to the present at a class level as a traditional spindle diagram. The width of the spindle represents the number of families as a rough estimate of diversity. The diagram is based on Benton, M. J. (1998) The quality of the fossil record of vertebrates. P. 269–303, in Donovan, S. K. and Paul, C. R. C. (eds), The adequacy of the fossil record, Fig. 2. Wiley, New York, 312 p. The figures representing classes are (from left): Agnatha, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves and Mammalia. The two extinct classes are Placodermi and Acanthodii. All classes interpreted traditionally. Bentons notes to his own tree: Number of families is an imperfect measure of diversity. Reptilia in particular should probably have been shown as far more diverse in the Mesozoic.
context_page_description: Evolutionary taxonomy, evolutionary systematics or Darwinian classification is a branch of biological classification that seeks to classify organisms using a combination of phylogenetic relationship, progenitor-descendant relationship, and degree of evolutionary change. This type of taxonomy may consider whole taxa rather than single species, so that groups of species can be inferred as giving rise to new groups. The concept found its most well-known form in the modern evolutionary synthesis of the early 1940s.
  Evolutionary taxonomy differs from strict pre-Darwinian Linnaean taxonomy, in that it builds evolutionary trees. While in phylogenetic nomenclature each taxon must consist of a single ancestral node and all its descendants, evolutionary taxonomy allows for groups to be excluded from their parent taxa, thus permitting paraphyletic taxa.
context_section_description: As more and more fossil groups were found and recognized in the late 19th and early 20th century, palaeontologists worked to understand the history of animals through the ages by linking together known groups. The Tree of life was slowly being mapped out, with fossil groups taking up their position in the tree as understanding increased.
  These groups still retained their formal Linnaean taxonomic ranks. Some of them are paraphyletic in that, although every organism in the group is linked to a common ancestor by an unbroken chain of intermediate ancestors within the group, some other descendants of that ancestor lie outside the group. The evolution and distribution of the various taxa through time is commonly shown as a spindle diagram (often called a Romerogram after the American palaeontologist Alfred Romer) where various spindles branch off from each other, with each spindle representing a taxon. The width of the spindles are meant to imply the abundance (often number of families) plotted against time.
  Vertebrate palaeontology had mapped out the evolutionary sequence of vertebrates as currently understood fairly well by the closing of the 19th century, followed by a reasonable understanding of the evolutionary sequence of the plant kingdom by the early 20th century. The tying together of the various trees into a grand Tree of Life only really became possible with advancements in microbiology and biochemistry in the period between the World Wars.
caption: Evolution of the vertebrates at class level, width of spindles indicating number of families. Spindle diagrams are often used in evolutionary taxonomy.
exif: {"Image Orientation": "Horizontal (normal)", "Image XResolution": "28", "Image YResolution": "28", "Image ResolutionUnit": "Pixels/Centimeter", "Image Software": "Adobe Photoshop 7.0", "Image DateTime": "2011:02:04 21:20:08", "Image ExifOffset": "156", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "294", "Thumbnail JPEGInterchangeFormatLength": "4771", "EXIF ColorSpace": "Uncalibrated", "EXIF ExifImageWidth": "734", "EXIF ExifImageLength": "509"}