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Chapter 34 Vertebrate Evolution and Diversity. Segmentation. Body plan in which structures are repeated, producing a series of body compartments that can be regulated independently, allowing body parts to become specialized
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Chapter 34 Vertebrate Evolution and Diversity
Segmentation • Body plan in which structures are repeated, producing a series of body compartments that can be regulated independently, allowing body parts to become specialized • Segmented animals are found within each of the three major clades of bilateral animals • Molecular data suggest that segmentation evolved independently three times
Four anatomical features that characterize the phylum Chordata
1. Embryos all have a common skeletal structure called a notochord. The notochord is a flexible rod located between the digestive tube and nerve chord. a. Provides skeletal support. b. In most vertebrates, it’s replaced by a jointed skeleton. c. Remains of the notochord exist as disks between the vertebrae. 2. Dorsal, hollow nerve cord a. Develops into the brain and spinal cord of the adult.
3. Pharyngeal slits Water enters through the mouth and passes out through the slits in the pharynx, without going through the digestive system. i. Slits function as suspension-feeding devices in many invertebrate chordates ii. Slits have been modified in more evolved vertebrates for: - Gas exchange - Hearing - Jaw support 4. Postanal tail Provides propulsion for swimming
B. Invertebrate chordates provide clues to the origin of vertebrates 1. Subphylum Urochordata Adult is sessile and feeds via pharyngeal slits.
2. Subphylum Cephalochordata a. Adult form shows chordate features. b. Adults feed and swim.
II. Introduction to the vertebrates A. Neural crest, enhanced cephalization, vertebral column, and a closed circulatory system characterize the subphylum Vertebrata 1. Neural crest a. Embryonic feature that allows for many unique vertebrate characteristics, e.g. bones and cartilage are formed from the neural crest cells throughout the body. b. Forms along the dorsal side of the embryo. Figure 34.6 (p. 683) – The neural crest, embryonic source of many unique vertebrate characters.
2. Skeletal elements, such as the cranium (braincase), allow for the big evolutionary feature of vertebrates, cephalization. This gives us the term “Craniates” 3. Vertebral column is the main support for the body axis. It allows for large size, fast movement, and protection of the nerve cord. 4. The closed circulatory system pumps oxygenated blood to cells and allows rapid metabolism, rapid movement to search for food, escape predators.
B. Overview of vertebrate diversity Figure 34.7 (p. 684) – Phylogeny of the major groups of extant vertebrates. **Note the three super groups: Gnathostomes, Tetrapods, Amniotes**
III. Jawless vertebrates A. These are the most primitive vertebrates. B. Groups include hagfish (no skeleton, no notochord in adult); lamprey (early version of a vertebral column). Figure 34.8 (p. 685) – A hagfish. Figure 34.9 (p. 685) – A sea lamprey.
IV. Fishes and amphibians A. Vertebrate jaws evolved from skeletal supports of pharyngeal slits 1. Animals that replaced jawless vertebrates, and are Gnathostomes. 2. Members of group have two pairs of fins. 3. Jaws and fins allowed fish to become active in pursuit of food and in biting off chunks of flesh. 4. Jaws evolved from modifications of skeletal elements of anterior pharyngeal gill slits.
5. Fishes were prevalent about 360 to 400 million years ago- the “Age of Fishes” 6. Two groups are alive today: a. Class Chondricthyes: Sharks and rays have cartilaginous skeletons Figure 34.11 (p. 688) – Cartilaginous fishes.
Lake trout Whitefish Sturgeon Great Lakes Walleye Some of the natives
Rainbow trout/brown trout Alewife Smelt Great Lakes Some Exotics Ruffe
Bluegill Yellow perch Great Lakes Some successors Largemouth bass
D. Tetrapods evolved from specialized fishes that inhabited shallow water Figure 34.15 (p. 690) – The origin of tetrapods. 1. The first tetrapods to spend much time on land were amphibians. Figure 34.17 (p. 691) – Amphibian orders. Order Urodela – Salamanders, retain tails as adults Order Anura – Frogs, lack tails as adults Order Apoda – Caecilians, lack legs
2. There were earlier tetrapods. These were specialized fish that • occupied shallow ponds, • breathed air by gulping, and • developed lobed walking fins for moving from one pond to another. 3. Why go on dry land? There were no other competitors for plants and insects that serve as food.
4. Amphibians need to return to water to lay eggs and for development of larvae. Figure 34.18 (p. 692) – The “dual life” of a frog.
V. Amniotes (includes reptiles, mammals, and birds) A. Evolution of the amniotic egg expanded the success of vertebrates on land Figure 34.19 (p. 693) – The amniotic egg.
1. Amniotic eggs allowed vertebrates to sever the link with water and live their whole lives on land. 2. Specialized membranes, called extra-embryonicmembranes that function in gas exchange, waste storage, and transfer of nutrients. a. Membranes develop from tissues derived from the embryo. b. One membrane, the amnion, gives the name for the amniotic egg.
B. Reptilian heritage is evident in all amniotes 1. Scales of keratin, waterproof skin - prevent dehydration. - Reptiles cannot breathe through skin, so all gas exchange occurs via lungs. 2. Shelled amniotic eggs require internal fertilization. Shell forms around fertilized egg in the reproductive tract. 3. Reptiles don’t use metabolism to regulate body temperature; they are ectotherms. Ectotherms absorb external heat (i.e. sunlight) Reptiles are able to survive on about 10% of calories required by mammals. 4. Oldest reptiles are from the late Carboniferous (about 300 million years ago) à dinosaurs and pterosaurs.
5. Modern reptiles include 6,500 species that are in four groups: a. Testudines – Turtles - Some species returned to water; all lay eggs on land. b. Sphenodontia – Tuataras c. Squamata – Lizards, snakes - Lizards are the most numerous group. - Snakes are descendants of lizards and have vestigial pelvic and limb bones. d. Crocodilia – Crocodiles, alligators - This is the group most closely related to dinosaurs Figure 34.24 (p. 697) – Extant reptiles.
