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. 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. 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. 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. 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. 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. 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 (ag.arizona.edu/tree/)
• Vertebrates
• Gnathostomata
• Terrestrial vertebrates (Tetrapods)
Updated by David Cannatella, September 18, 2001