Animal phylogeny based on sequencing of SSU-rRNA
Chordata- vertebrates
Phylum Chordata
Chordate Characteristics
• Distinguishing Features
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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
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Subphylum Vertebrata: in search
of a diagnostic feature
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3 chordate characteristics
Segmentation
Cephalization
Vertebrae
Cranium
Endoskeleton
*NEURAL CREST MATERIAL*
Fish
• Classification of Fish
Seven Extant Classes of
Vertebrates
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Agnatha - jawless fishes
Chondrichthyes - cartilagenous fishes
Osteichthyes - bony fishes
Amphibia - amphibians
Reptilia - reptiles
Aves - birds
Mammalia - mammals
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
Hagfish
Notochord; 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
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Ventilation
Feeding
Sensory
Osmoregulation
Reproduction
Class Chondrichthyes
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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
of Animal Life
1. Gas exchange
2. Nutrition
3. Distribution and transport
4. Disposal of cellular wastes
5. Internal water and salt balance
6. Reproduction and development
7. Support and movement
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Vertebrate Invasion Onto Land
A coelocanth (Latimeria), the only extant lobe-finned genus
• Demands of terrestrial life:
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How to move on land?
How to exchange gases?
How to prevent desiccation?
How to reproduce and develop?
Amphibians: the first tetrapods
• 3 Orders
– Urodela - salamanders and newts
– Anura - frogs and toads
– Apoda - caecilians (legless amphibs)
• General Features
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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
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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
Archaeopteryx sp.
• Reptile-like characteristics
– Reptilian jaw
– Claws
– Tail
– Solid bones
• Bird-like characteristics
– Feathers - modified scales
– Posture
– Large avian eye
Archaeopteryx, a Jurassic bird-reptile
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Avian Characteristics
1. Endothermic Homeotherms
2. Feathers
3. Hollow bones
4. Skeletal fusion
5. Loss of tail
6. Beak
7. Gizzard
8. Digestive and urinary changes
9. Respiratory changes
10. Circulatory changes
11. Reproductive changes
12. Parental care
Form fits function: the avian wind and feather
A bald eagle in flight
Mammalian Characteristics
1. Endothermic Homeotherms
2. Hair or fur covering
3. Mammary glands
4. Single boned jaw
5. Heterodont dentition
6. Rearrangement of pectoral and
pelvic girdles
7. Circulatory changes
8. Respiratory changes
9. 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 extraembryonic membranes
Placenta
Evolutionary 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
of Animal Life
1. Gas exchange
2. Nutrition
3. Distribution and transport
4. Disposal of cellular wastes
5. Internal water and salt balance
6. Reproduction and development
7. Support and movement
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