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Chordata- vertebratesAnimal phylogeny based on sequencing of SSU-rRNA

Phylum Chordata• Distinguishing Features

– 1. Pharyngeal gill slits– 2. Dorsal hollow nerve cord– 3. Notochord– 4. Muscular postanal tail

• 3 Chordate Subphyla:– Urochordata - tunicates (invert.)– Cephalochordata - lancelets (invert.)– Vertebrata - fishes, amphibians, reptiles, birds and

mammals

Chordate Characteristics

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Subphylum Vertebrata: in search of a diagnostic feature

• 3 chordate characteristics• Segmentation• Cephalization• Vertebrae• Cranium• Endoskeleton• *NEURAL CREST MATERIAL*

Seven Extant Classes of Vertebrates

• Agnatha - jawless fishes• Chondrichthyes - cartilagenous fishes• Osteichthyes - bony fishes• Amphibia - amphibians• Reptilia - reptiles• Aves - birds • Mammalia - mammals

Fish

• Classification of Fish

Cl. Agnatha and Cl. Placoderma• Agnathans - Ancestral vertebrates: 470-500 mya

…extinct by 370 mya• Modern representatives: cartilage skeleton,

smooth skin, retain notochord– Lampreys and Hagfish

• Cl. Placoderma: (410-350 mya)• Two important innovations: jaws and fins

HagfishNotochord; slime!; cartilaginous skeleton; poor eyes; slime (I know, but its worth mentioning twice…)

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Class Chondrichthyes: sharks, skates and rays

• Bouyancy control– Cartilagenous skeleton

• Adaptations of sharks, skates and rays– Ventilation– Feeding– Sensory– Osmoregulation– Reproduction

Class Chondrichthyes• Cartilaginous Fish• Jaws; scales; spiral valve in intestine; pared gills• Subclass Elasmobrachii- Sharks, skates, rays• Subclass Holocephali- Chimaeras

Class Ostiechthyes: bony fishes• General features• Evolution in freshwater: lungs• Divergence of bony ancestor into 2 groups

– Ray finned fishes – lobe finned fishes and lungfish

Figure 34.12a Ray-finned fishes (class Actinopterygii): yellow perch

Counter-current gas exchange 7 Basic Requirements 7 Basic Requirements of Animal Lifeof Animal Life

1. Gas exchange2. Nutrition3. Distribution and transport4. Disposal of cellular wastes5. Internal water and salt balance6. Reproduction and development7. Support and movement

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Vertebrate Invasion Onto Land• Demands of terrestrial life:

– How to move on land?– How to exchange gases?– How to prevent desiccation?– How to reproduce and develop?

A coelocanth (Latimeria), the only extant lobe-finned genus

Amphibians: the first tetrapods• 3 Orders

– Urodela - salamanders and newts– Anura - frogs and toads– Apoda - caecilians (legless amphibs)

• General Features– Locomotion– Feeding– Gas exchange– Osmoregulation– Circulation– Reproduction and development

• Metamorphosis– Hearing and voice

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Figure 34.18 “Dual life” of a frog (Rana temporaria)

Modern Reptiles: Adaptations• Desiccation resistant

covering• Respiratory changes• Reproductive advances:

– amniotic egg– extraembryonic membranes

Amniotic Egg

Tiny intermolecular forces - van der Waals forces - are produced by literally billions of tiny hair-like structures,

or spatulae, on each gecko toe. unbalanced electrical charges around molecules attract one another

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“Geckro” Birds and Mammals

• Temperature and metabolic rate• Poikilotherms: reptiles• Homeotherms: mammals and birds• Ectothermy• Endothermy

Why cold-blooded and warm-blooded doesn’t cut it…

Ancient Birds: Archaeopteryx

• Reptile-like characteristics– Reptilian jaw– Claws– Tail

– Solid bones

• Bird-like characteristics– Feathers - modified scales– Posture– Large avian eye

Archaeopteryx sp.

Archaeopteryx, a Jurassic bird-reptile

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Avian Characteristics1. Endothermic Homeotherms2. Feathers3. Hollow bones4. Skeletal fusion5. Loss of tail6. Beak7. Gizzard8. Digestive and urinary changes9. Respiratory changes10. Circulatory changes 11. Reproductive changes12. Parental care

Form fits function: the avian wind and feather A bald eagle in flight

Mammalian Characteristics1. Endothermic Homeotherms2. Hair or fur covering3. Mammary glands4. Single boned jaw5. Heterodont dentition6. Rearrangement of pectoral and

pelvic girdles7. Circulatory changes8. Respiratory changes9. Reproductive Adaptations

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Australian monotremes and marsupials: echidna (top left), marsupial mouse (lower left), sugar glider (right) Mammalian Reproductive Strategies:

• Monotremes: Echidna and Duck-billed platypus

• Marsupials: premature delivery

• Placental Mammals: – internal development– Reuse of extra-

embryonic membranes

PlacentaEvolutionary convergence of marsupial and eutherian

(placental) mammals

• Move from trees onto ground

• Concomitant morphological changes

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Hominid Evolution• Lucy ~ 3.5 mya

7 Basic Requirements 7 Basic Requirements of Animal Lifeof Animal Life

1. Gas exchange2. Nutrition3. Distribution and transport4. Disposal of cellular wastes5. Internal water and salt balance6. Reproduction and development7. Support and movement