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  1. 1. Comparative Anatomy page 1 Vertebrate Phylogeny You need to know the phylogeny on the following page extremely well. It is crucial to understanding the evolution of various anatomical systems. Don't just memorize the tree. Work with it and understand how it is put together. Classification T he traditional classification (in the Kardong textbook, Appendix D, pp. 696-698) of the living vertebrates places them in superclass Agnatha, and classes Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, and Mammalia. Of these only the Chondrichthyes, Aves, and Mammalia are monophyletic. The others (Agnatha, Osteichthyes, Amphibia, Reptilia) are paraphyletic. In this course, we either redefine the content of these taxa so that they are monophyletic, or we abandon usage of the names. Some taxa whose names we have redefined are Reptilia, Osteichthyes, Sarcopterygii, Amphibia, and Synapsida. These are redefined to be monophyletic by having the ancestor include all, rather than only some, of its descendants. For example, Reptilia now includes all of its descendants, including Aves (birds). Amphibia, which formerly included all early Tetrapoda, but excluded reptiles, birds, and mammals, now only includes the ancestor of living amphibians and all of the descendants of that ancestor. See the figures on the next page. Taxon names that are capitalized are proper nouns, and represent monophyletic taxa. If names that refer to paraphyletic groups are used, they are used informally and are not capitalized, or else put in quotes (e.g., agnathans or quot;Agnathaquot;). Two of the pages below indicate several commonly used paraphyletic groups. Don't even worry about learning the classifications given in your textbook on pp. 696 and in the lab book on pp. 32-33.
  2. 2. Comparative Anatomy page 2 Hemichordata Urochordata Cephalochordata Chordata Euchordata Myxinoidea Petromyzontidae Craniata Chondrichthyes Elasmobranchii Vertebrata Holocephali Brachiopterygii Actinopterygii Chondrostei Gnathostomata Lepisosteus Amia Neopterygii Teleostei Osteichthyes Actinistia Dipnoi Gymnophiona Sarcopterygii Amphibia Caudata Choanata Anura Monotremata Mammalia Eutheria Tetrapoda Marsupialia Theria Testudinata Amniota Sphenodontia Lizards Lizards Reptilia Lizards Amphisbaenia Sauria Ophidia Squamata Lepidosauria Aves Crocodylia Archosauria Fall 2001
  3. 3. Comparative Anatomy page 3 Phylogenetic Taxonomy of Living Vertebrates A phylogenetic taxonomy of living vertebrates is given below as an indented list; no fossils are included (yet). A quot;phylogeneticquot; taxonomy means that the tree can be derived exactly from this list, and vice-versa. The placement of certain fossils will be discussed as they become relevant to the course. Notice that no ranks (e.g., order, subclass) are used. The cladistic classification (p. 699) in Kardong is an attempt to do the same thing, but it is not very well done, so please ignore it. Craniata Myxinoidea Vertebrata Petromyzontia Gnathostomata Chondrichthyes Holocephali Elasmobranchii Osteichthyes Actinopterygii Brachiopterygii Unnamed taxon Chondrostei Neopterygii Lepisosteus Unnamed taxon Amia Teleostei Sarcopterygii Actinistia Choanata Dipnoi Tetrapoda Amphibia Gymnophiona Batrachia Anura Urodela Amniota Mammalia Monotremata Theria Marsupialia Eutheria Reptilia Testudines Sauria Lepidosauria Sphenodontia Squamata Archosauria Crocodylia Aves
  4. 4. Comparative Anatomy page 4 Hemichordata Nonmonophyletic groups, I Urochordata Cephalochordata Myxinoidea Petromyzontia quot;Invertebrataquot; Chondrichthyes Actinopterygii Actinistia Dipnoi Amphibia Mammalia quot;Piscesquot; Testudinata quot;Crossopterygiiquot; quot;Homothermiaquot; Lepidosauria quot;Reptiliaquot; Crocodylia Aves
  5. 5. Comparative Anatomy page 5 Hemichordata Nonmonophyletic groups, II Urochordata Cephalochordata Myxinoidea Petromyzontia Chondrichthyes Actinopterygii Actinistia Dipnoi quot;Agnathaquot; Amphibia Mammalia quot;Osteichthyesquot; quot;Sarcopterygiiquot; Testudinata quot;Amphibiaquot; Lepidosauria quot;Labyrinthodontiaquot; quot;Synapsidaquot; Crocodylia Aves
  6. 6. Comparative Anatomy page 6 Numbers of Living Species of Chordates There are about 50,000 species of living vertebrates; this estimate varies, primarily depending on how many species of teleost fishes are recognized. Clade Name Species Common Name Hemichordata 100 acorn worms, pterobranchs Urochordata (tunicates) 2000 sea squirts, larvaceans Cephalochordata 45 amphioxus or lancelets Myxinoidea 30 hagfish Petromyzontia 40 lampreys Chondrichthyes Elasmobranchii 670 sharks, skates, rays Holocephali 30 ratfish or chimaeras Actinopterygii Brachiopterygii 13 reedfish or bichirs Chondrostei 22 sturgeon, paddlefish Lepistosteus 7 gar Amia 1 bowfin or choupique Teleostei 25000 tarpon, herring, perch, catfish, minnows, bass, etc. Actinistia 1 (maybe coelacanth (Latimeria) 2) Dipnoi 6 lungfish Amphibia Gymnophiona *160 caecilians Caudata *350 salamanders Anura 5000 frogs Mammalia Monotremata 6 platypus, echidna Marsupialia 240 opposum, kangaroos, koalas, wombats, etc. Eutheria 4300 mice, elephants, horses, whales, bats, cats, etc. Testudinata +230 turtles, tortoises, terrapins Lepidosauria Sphenodontia 2 tuatara (Sphenodon) Squamata lizards +3000 lizards Ophidia +2330 snakes Amphisbaenia +140 amphisbaenians Aves 8700 birds Crocodylia +21 alligators, crocodiles, gavials Numbers from Walker, 1987 and Wake, 1979, except as noted. *Duellman and Trueb, 1986 +Dowling and Duellman, 1978
  7. 7. Comparative Anatomy page 7 Geological Time Scale If the entire geological history of earth were set to a one-year scale, the earth formed on 1 January, life appeared on 4 April, and Homo sapiens did not appear until very late on New Year's Eve. One-Year Scale Real Time Event 1 Jan 4.6 by Origin of the earth 4 Apr 3.8 by Life appears (bacteria) 9 Nov 650 my Marine invertebrates appear 20 Nov 520 my Vertebrata 29 Nov 415 my Ostracoderms 30 Nov 410 my Gnathostomata (acanthodians) Actinopterygii 2 Dec 380 my Chondrichthyes 3 Dec 360 my Tetrapoda 7 Dec 310 my Amniota 16 Dec 190 my Mammalia 20 Dec 150 my Aves 26 Dec 65 my Primates 29 Dec 30 my Anthropoidea (monkeys and apes) 11:45 pm 31 Dec 125-250,000 yr Homo sapiens Check out these web pages on the Tree of Life ( • Vertebrates • Gnathostomata • Terrestrial vertebrates (Tetrapods) Updated by David Cannatella, September 18, 2001