evolution of the phylum chordata

4: Evolution of the Phylum Chordata

5: THE PHYLUM CHORDATA I. Unifying Features of Vertebrates A. Generalized body plan 1. Diagnostic features - present sometime during the development or life of all Chordates. a. Dorsal, hollow nerve cord b. Pharyngeal gill slits c. Notochord - originally a cord of living cells; becomes part of the centrum of vertebrates up through primitive reptiles; incorporated into intervertebral discs in birds and mammals.

7: Other Features of Chordates B. Pharynx - gill slits develop as outgrowths of pharyngeal endoderm and are paired C. Fate of gill slits 1. 8 is the largest number formed in vertebrates; 15 in lampreys 2. 1-3 retained in gilled salamanders 3. 4 slits in frog tadpoles 4. 3 rupture through in birds and then close; except 1 becomes Eustachian tube

8: C. Fate of Gill Slits (cont.) 5. 1 or 2 rupture through in mammals; 1 becomes the Eustachian tube 6. Original function of gill slits is for filter feeding - not respiration 7. Most gill pouches contribute to other organs

9: Still Other Features D. Pharyngeal arches - four basic structures 1. Pharyngeal skeletal element 2. Branchiomeric muscle element 3. Branches of nerves 4. Aortic arches - arteries that contribute to other arterial structures

10: And Still More E. Dorsal-hollow nerve cord 1. Formation - forms from neural folds of ectoderm on dorsal surface of the embryo. F. Other basic features 1. Integument - skin; protective covering that can serve for respiration; sweat and mammary glands form here; other structures such as nails, horns, feathers, hair, scales 2. Respiration - can occur through skin, via gills, or via lungs

11: Plus More Yet 3. Coelom - internal body cavity whose lining forms entirely from mesoderm Pericardial cavity surrounds the heart Pleuroperitoneal cavity surrounds the lungs Parietalperitoneal cavity surrounds abdominal viscera

12: And Finally . . . 4. Digestive system - complete digestive system with mouth and anus 5. Urogenital system - comprised of excretory and reproductive systems which form in unison and share common ducts. 6. Circulatory system - closed system usually with a pumping heart and differentiation of arteries and veins. 7. Sense Organs - more numerous and often more developed than in invertebrates

13: II. Origin of the Phylum Chordata A. Echinoderm theory - theory that Echinoderms and Chordates had a common ancestor. 1. Mesoderm formation - forms by pouching of solid masses of tissues in Echinoderms and Chordates

14: 2. Larval forms - Some Echinoderms and primitive relatives of Chordates (protochordates) have a free-living tornaria larva

15: 3. Biochemical similarity - Echinoderms and Chordates have similar amino acid sequences for blood proteins and both utilize creatine phosphate as a storage compound for P that is released to make ATP in muscle; all other animals utilize argenine phosphate 4. Developmental similarity In both Echinoderms and Chordates, the blastopore of the developing embryo becomes the anus; among other animals the blastopore becomes the mouth.

16: Relationship to Classification of Animals Echinoderms and Chordates are referred to as Deuterostomes All other animal phyla are referred to as Proterostomes.

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18: SURVEY OF PHYLUM CHORDATA I. Evolutionary History A. Subphylum Urochordata - sessile tunicates that have a free-living tadpole larva B. Subphylum Cephalochordata - filter-feeding Amphioxus or lancets

19: C. Evolution of Vertebrata II. Class Cyclostomata (Agnatha) A. General features of modern agnathans 1. no scales 2. notochord large in adult - only skeletal component 3. single nostril located dorsally - both nostrils fused into one 4. lack paired fins

20: Early Fishes B. Ostracoderms 1. Extinct armored, jawless fishes of the Ordivician 2. poorly developed paired fins 3. eyes located dorsally 4. bony armor in skin

21: First Jawed Fishes III. Class Placodermi A. General features 1. Extinct, jawed fishes of the Devonian 2. boney skeleton 3. paired fins 4. along direct line to modern fishes

22: Cartilagenous Fishes V. Class Chondrichthyes A. General features 1. skeleton of cartilage - secondary loss of ossification 2. teeth derived from scales 3. placoid scales 4. both egg-laying and live- bearing, with 2-chambered ht.

23: Bony Fishes V. Class Osteichthyes A. General features l. Jawed fishes with paired fins 2. 2-chambered ht. 3. scales of various types 4. ectothermic 5.represent modern fishes

24: Terrestrial Vertebrates VI. Class Amphibia A. General features 1. semi-terrestrial tetrapods- return to water to breed 2. respire by lungs or the integument 3. ectothermic 4. 3-chambered ht. 5. frogs, toads, salamanders, caecelians

25: Complete Invasion of Land VII. Class Reptilia A. General features 1. first amniotes and fully terrestrial 2. incomplete 4-chambered ht. 3. ectothermic 4. scales 5. dominant during the Mesozoic Era

26: Aerial Vertebrates VIII. Class Aves A. General features 1. Endothermic 2. lack teeth (some extinct forms had teeth) 3. feathers for flight surface and temperature regulation 4. 4-chambered ht. 5. all oviparous

27: Furry Things IX. Class Mammalia A. General features 1. Endothermic 2. Hair for thermoregulation 3. Mammary glands 4. 4-chambered ht. 5. viviparous (except for monotremes which lay eggs)