CHpt 34? FR

Chapter 34: Vertebrates 🐟🦎🐸🐦🐘

Big Picture

Vertebrates = chordates with a backbone.

Major evolutionary innovations:

1. Notochord + dorsal hollow nerve cord → chordates

2. Backbone + skull → vertebrates

3. Jaws + mineralized skeleton → gnathostomes

4. Lobed fins → limbs with digits → tetrapods

5. Amniotic egg → amniotes

6. Hair + milk → mammals

Humans are: Chordates → Vertebrates → Gnathostomes → Osteichthyans → Lobe-fins → Tetrapods → Amniotes → Mammals

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34.1 Chordates Have a Notochord and a Dorsal Hollow Nerve Cord

Four Derived Characters of Chordates

1. Notochord

• Flexible rod running along body

• Provides support during movement

• In vertebrates mostly replaced by backbone

• In humans remains as intervertebral disk material

2. Dorsal Hollow Nerve Cord

• Develops into brain and spinal cord

• Unique to chordates

• Located above notochord

3. Pharyngeal Slits/Clefts

• Openings in pharynx

• Filter feeding in invertebrate chordates

• Become gills in fishes

• Form ear/head structures in tetrapods

4. Post-Anal Tail

• Extends beyond anus

• Helps swimming

• Reduced in humans during development

Chordate Groups

Lancelets (Cephalochordata)

• Retain all chordate traits as adults

• Suspension feeders

• Burrow in seafloor

Tunicates (Urochordata)

• Larvae show all chordate traits

• Adults lose most traits

• Sessile “sea squirts”

Evolutionary Importance

• Lancelets resemble early chordates

• Tunicates share genes linked to vertebrate organs

• Help explain origin of vertebrates

Remember:

N-D-P-P

• Notochord

• Dorsal hollow nerve cord

• Pharyngeal slits

• Post-anal tail

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34.2 Vertebrates Are Chordates That Have a Backbone

Major Vertebrate Innovations

• Backbone (vertebrae)

• Skull

• Larger brain

• Complex nervous system

• Neural crest cells

Neural Crest

Unique vertebrate embryonic cells that form:

• Skull bones

• Teeth

• Cartilage

• Sensory organs

• Neurons

Hagfishes

• Jawless

• Marine scavengers

• Produce defensive slime

• Retain notochord as adults

Lampreys

• Jawless

• Some are parasites

• Feed on fish blood/tissues

• Cartilage skeleton

Early Vertebrate Evolution

Haikouella

• Early chordate

• Brain and eyes

• No skull

Myllokunmingia

• First chordate with a head

• Had skull parts

• Lived ~530 MYA

Conodonts

• Earliest vertebrates

• Mineralized dental structures

• Predators

Key Trend

Skeleton evolution:

Cartilage → Mineralized bone → Internal bony skeleton

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34.3 Gnathostomes Are Vertebrates That Have Jaws

Gnathostomes = Jawed Vertebrates

Includes:

• Sharks

• Rays

• Bony fishes

• Amphibians

• Reptiles

• Birds

• Mammals

Advantages of Jaws

• Better feeding

• Stronger predation

• More efficient food processing

Other Gnathostome Traits

• Paired fins

• Enlarged forebrain

• Better vision and smell

• Lateral line system

Fossil Gnathostomes

Placoderms

• Armored fishes

• Included giant predator Dunkleosteus

Acanthodians

• Early jawed fishes

• Extinct

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Chondrichthyans (Cartilaginous Fishes)

Examples:

• Sharks

• Rays

• Skates

• Chimaeras

Characteristics:

• Cartilage skeleton

• Internal fertilization

• Powerful jaws

• Excellent senses

Shark Adaptations

• Oil-filled liver for buoyancy

• Electroreception

• Acute smell

• Continuous swimming

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Osteichthyans (Bony Vertebrates)

Characteristics:

• Bony skeleton

• Operculum covers gills

• Swim bladder

• Scales + mucus

Ray-Finned Fishes

• 27,000 species

• Most fish species

• Flexible fin rays

Lobe-Finned Fishes

• Fleshy fins with bones

• Ancestors of tetrapods

Examples:

• Coelacanths

• Lungfishes

• Tetrapods

Exam Favorite

Swim bladder evolved from lungs.

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34.4 Tetrapods Are Gnathostomes That Have Limbs

Tetrapod Derived Traits

• Four limbs with digits

• Neck

• Strong pelvic girdle attached to backbone

• Reduced/lost gills as adults

Origin of Tetrapods

Evolved from lobe-finned fishes.

Tiktaalik (VERY IMPORTANT)

Transitional fossil between fish and tetrapods.

Fish traits:

• Scales

• Fins

• Gills

Tetrapod traits:

• Neck

• Ribs

• Wrist bones

• Limb-like fins

Evolution Sequence

Lungfish → Eusthenopteron → Panderichthys → Tiktaalik → Acanthostega → Tetrapods

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Amphibians

Three Groups

Salamanders (Urodela)

• ~550 species

• Some aquatic, some terrestrial

Frogs (Anura)

• ~5,400 species

• Strong hind legs

• Sticky tongue

Caecilians (Apoda)

• Legless

• Burrowing

• Worm-like

Amphibian Characteristics

• Moist skin

• Eggs lack shell

• Depend on water for reproduction

• Gas exchange through skin

Life Cycle

Egg → Tadpole → Adult

Tadpole:

• Gills

• Tail

• Herbivore

Adult:

• Lungs

• Legs

• Carnivore

Population Decline Causes

• Chytrid fungus (Bd)

• Habitat loss

• Pollution

• Climate change

Why Amphibians Are Sensitive

• Permeable skin

• Depend on both aquatic and terrestrial habitats

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34.5 Amniotes Are Tetrapods That Have a Terrestrially Adapted Egg

Amniotes Include

• Reptiles (including birds)

• Mammals

Amniotic Egg

Contains 4 membranes:

Amnion

• Cushions embryo

Chorion

• Gas exchange

Yolk Sac

• Nutrients

Allantois

• Waste storage + gas exchange

Importance

Allowed reproduction away from water.

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Reptiles

Characteristics:

• Keratin scales

• Internal fertilization

• Shelled eggs

• Ectothermic (except birds)

Major Groups

Turtles

• Shell fused to ribs and vertebrae

Lepidosaurs

• Tuataras

• Lizards

• Snakes

Archosaurs

• Crocodilians

• Dinosaurs

• Birds

Dinosaurs

Two major groups:

Ornithischians

• Herbivores

Saurischians

• Includes theropods

• Ancestors of birds

Extinction

Non-avian dinosaurs went extinct 66 MYA.

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Birds

Birds are living dinosaurs.

Adaptations for flight:

• Feathers

• Hollow bones

• Large pectoral muscles

• Efficient lungs

• High metabolism

Archaeopteryx

Important transitional fossil linking dinosaurs and birds.

Bird Facts

• ~10,000 species

• Internal fertilization

• Brood eggs

• Complex behaviors

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Mammals

Mammalian Traits

• Hair

• Mammary glands (milk)

• Endothermy

Three Groups

Monotremes

• Lay eggs

• Example: platypus

Marsupials

• Short gestation

• Pouch development

• Example: kangaroo

Eutherians (Placental Mammals)

• Complex placenta

• Long gestation

• Most mammals

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Chapter 34 Must-Know Evolution Path

Chordates

↓

Vertebrates

↓

Gnathostomes (jaws)

↓

Osteichthyans (bony skeleton)

↓

Lobe-Fins

↓

Tetrapods (limbs)

↓

Amniotes (amniotic egg)

↓

Mammals (hair + milk)

↓

Humans

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10 Exam Facts to Memorize

1. Chordates = notochord, dorsal hollow nerve cord, pharyngeal slits, post-anal tail.

2. Neural crest is unique to vertebrates.

3. Hagfishes and lampreys are jawless vertebrates.

4. Gnathostomes = jawed vertebrates.

5. Jaws evolved from modified gill-support structures.

6. Osteichthyans have bony skeletons.

7. Tetrapods evolved from lobe-finned fishes.

8. Tiktaalik is the classic fish-to-tetrapod transitional fossil.

9. Amniotic egg allowed reproduction on land.

10. Birds evolved from theropod dinosaurs. 🦖➡🐦