Exercise 4: Cladograms This exercise is based on the data in Table 1 on p. 462 of your textbook. Please correct the error in Table 1 before you start the exercise: Mammals have a+ for the character "mammary glands." Construct a complete cladogram based on these data. Continue the first steps provided in Figures la and 1b, and resolve for all ten clades provided in Table 1. Note that your cladogram must be the most parsimonious model possible. The derived character that defines a particular clade must be included in your cladogram (see Figures la and 1b). Scanned hand drawings are acceptable for submission as long as they are clear and legible./nConstructing a Cladogram Research Method Cladograms allow systematists (and Box others) to visualize hypothesized evolutionary relationships by grouping organisms that share derived characters. The cladogram also indicates where derived characters evolved. Table 1 Lancelets Lampreys Sharks Bony fishes Amphibians Mammals Turtles Lizards Crocodilians Birds Here we develop a cladogram for the nine extant groups of chordate vertebrates: lampreys (Agnatha), sharks (Chondrichthyes), bony fishes (Osteichthyes), amphibians (Am- phibia), reptiles (turtles, lizards and snakes, crocodilians), birds, and mammals (see also Chapter 28). We also include lancelets (marine organisms in the subphylum Cephalo- chordata). Lancelets serve as the outgroup in our comparison. We have chosen characters on which to base the cladogram (Table 1), Vertebrae Jaws Figure 1 (a) A cladogram showing the separation of lancelets from living chordates. (b) A cladogram showing the separation of lancelets and lampreys from most living chordates. Lampreys are chor dates, but the cladogram suggests that they are the earliest chordates. These cladograms were prepared from the data in Table 1. + + + + + + + + + Swim Bladder Paired Extraembryonic Mammary Dry, Scaly or Lungs Limbs Membranes Glands Skin + noting the presence (+) or absence (-) of 10 different characters. The characters are ancestral or derived in each group, but the outgroup (the lancelets) lacks all of these traits. We construct the cladogram from the information in the table, grouping organisms that share derived characters (right branch, Figure 1a). whereas the lancelets form the left branch because they lack the derived characters. + + + The remaining organisms except lancelets and lampreys have jaws. Now the right branch (Figure 1b) includes all living vertebrates sharing derived characters, separating them from lancelets and lampreys. The selection of different characters might give different outcomes. + Lancelets b. Amphibians, birds, bony fishes, crocodilians, lampreys. lizards, mammals, sharks, turtles Amphibians, birds, bony fishes, crocodilians, lampreys, lizards, mammals, Lancelets Lampreys sharks, turtles U Vertebrae + Two One Openings at Opening in Back of Skull Front of Eye Feathers

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