Tuesday, March 6th

Vertebrates

FIRST – answer yesterday’s Q’s

• Turtles– Have an ectoskeleton (shell) and endoskeleton

(bones)– “Baby turtles shells are much like human babies

skulls. When born the plates are not fused or connected in any way. Nonetheless, over time the bonelike plates will grow together and once the turtle has reached its maximum size the plates will begin to fuse together.”

http://www.bio.davidson.edu

Shoulder blades fuse with shell – so cannot “molt” its shell – it’s

connected!

Compound Eyes

• http://andygiger.com/science/beye/beyehome.html

Q. If you cut an earthworm

in two, will it live?

• A. The rear half will always die, and the front half may live to become another whole worm. This is called regeneration. The front part must be long enough to contain the clitellum and at least 10 segments behind the clitellum. This makes up about half the length of the worm. The new posterior segments grown will be slightly smaller in diameter than the original segments and sometimes a bit lighter in color.

Overview of Today• Chordates (fishes, amphibians, reptiles, birds,

mammals)– Nonvertebrate Chordates (35.2)– Vertebrate Chordates (35.1)

• Fishes (35.4)• Amphibians (35.5)• Reptiles (35.6)• Birds (35.7)• HOMEWORK: Mammals (35.8) and Evolution

of Primates (35.9) pages 716-726 & NOTES

Chordates

• Fishes, amphibians, reptiles, birds, mammals• Characterized by 4 Features (during development):• 1. Single, hollow nerve chord (becomes brain/spine)• 2. Notochord, flexible rod below nerve chord• 3. Pharyngeal Slits/Pouches –become gills or

disappear• 4. Postanal Tail – some keep it, others lose it

Nonvertebrate Chordates

• Two subphyla: Urochordata (sea peach) and Cepalochordata (lancelets)

Vertebrate Chordates• Five Distinct Characteristics:• 1. Vertebral Column – notochord is replaced

by vertebrae that enclose and protect dorsal nerve chord

• 2. Head – distinct and well-differentiated head with skull make of bone or cartilage

• 3. Neutral Crest – particular group of embryonic cells that form a plate during development

Vertebrate Chordates

• 4. Internal Organs – liver, kidneys, endocrine glands (secrete hormones)

• 5. Endoskeleton – made of cartilage or bone (living tissue as compared to dead chitin), skeleton allows for great size and powerful movement

Overview of Vertebrate Evolution

• First vertebrates evolved in the ocean, 545 mya• Amphibians evolved and invaded the land• Amphibians gave rise to reptiles, 300 mya• 250 mya reptiles better suited to live on land –

dominate the land• Gave rise to birds and mammals• Dinosaurs & Mammals appear in fossil record

dated to 220 mya

Fishes• Most diverse vertebrate group• Ancestors to amphibians (“fish out of water”)• First fish sucked up small food particles from

ocean floor• Toothless and jaw-less

5 Key Characteristics

• 1. Vertebral Column • 2. Jaws and paired appendages - can eat larger

things, and have 4 fins• 3. Internal Gills – extract oxygen from water• 4. Single-Looped Blood Circulation – blood

pumped from heart to gills, passes to rest of body, back to heart

• 5.Nutritional Deficiences – cannot make aromatic amino acids, so they must consume them

Evolution of the Jaw & Teeth

Swim Bladder

• Swim Bladders help even out weight of bones so fish don’t sink

• Can regulate buoyancy• Sharks don’t have this, so they must

constantly swim to avoid sinking• Gas is harvested from blood, reabsorbed

when they want to “dive”

Amphibians• You guessed it… FIVE distinguishing features:• 1. Legs – most have 4• 2. Lungs – most have a pair• 3. Cutaneous Respiration –breathe through their

skin, which must remain moist, supplement lungs• 4. Pulmonary veins – pump blood after it exits

lungs• 5. Partially divided heart – keeps oxygenated and

deoxygenated blood separate = MORE EFFICIENT (but not perfect – no dividing wall in the ventricle)

Amphibians Overcame Terrestrial Challenges

• Amphibia = “Double Life”• Large Bodies required support• Breathe Air• Need more Oxygen to support larger muscles• Reproduction still in water• Body itself couldn’t dry out

Reptiles• This time, only THREE Key Characteristics… Phew!• 1. Amniotic Eggs – eggs must be laid in water /

moist setting (yolk sac provides food for embryo just like endosperm does for seeds)

• 2. Dry Skin – (unlike amphibians, who have moist skin) watertight, scales with keratin (claws, fingernails, hair)

• 3. Thoracic Breathing – squeezing throat to pump air into lungs

Reptile Fact

• Ectothermic – obtain heat from external sources

• Humans are Endothermic – we generate our own heat

• Turtles, tortoises, lizards, snakes, crocodiles, alligators

Birds• ONLY TWO CHARACTERISTICS! YAHOO!!• 1. Feathers – modified from reptilian scales;

provide lift and conserve heat• 2. Flight Skeleton – bones are thin and hollow;

many are fused, creating a more rigid body

• Crows, mockingbirds, hummingbirds, woodpeckers, parrots, doves, eagles, chickens, quail, cranes, swans, ducks, geese, owls, storks, penguins, kiwis, ostriches

Birds

• Endothermic, like mammals, are endothermic (example of convergent evolution)

• Efficient circulation and respiration – required to maintain flight