Vertebrate Chordates
Class Amphibia (“two lives”) – Invasion of Land
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Fossils dating back 360 million years ago
Frogs, toads, salamanders, caecilians
4,800 species (3,000 species of frogs and toads identified)
Most abundant in damp habitats: swamps, rainforests
Metamorphosis
Fertilization is external for majority
Eggs lack shell
Key adaptation to survival on land
 Formation of lungs
 Evolution of walking legs
 Changes in the circulatory system – three chambered heart
Class Amphibia
Order Eurodella (“tailed ones”)
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Salamanders
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Some are entirely aquatic
Others live on land as adults or throughout their life
500 species
Phylum Chordata
Class Amphibia (“two lives”)
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4,800 species
Frogs, toads, salamanders, cacilians
Most abundant in damp habitats:
swamps, rainforests
Fertilization is external for majority
Metamorphosis
Eggs lack shell
Class Amphibia
Order Apoda (“without legs”)
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Caecilians
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150 species
Mainly burrowing amphibians
Legless
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Nearly blind
Tropical habitat
Order Anura (“tailless ones”)
Frogs and Toads
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4,200 species
Lacks tail as an adult
“Dual life” of a frog (Rana temporaria)
The origin of tetrapods
Skeleton of Acanthostega, a Devonian tetrapod fish
Amphibian orders: Newt (left), frog (right)
A hypothetical phylogeny of amniotes
Taxonomic classes of amniotes
Vertebrate Chordates
Class Reptilia
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Examples: lizards, snakes, crocodiles, etc.
Special adaptations of reptiles
 Dry skin covered with scales that efficiently retard water
 Have amniotic eggs
 Yolk, albumen = food supply
 Amnion
 Leathery (hard) shell
 Internal fertilization
 Three-chambered heart
 Ectotherms
Amniotic egg anatomy
A hatching reptile
Snakes
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24,000 living species
Snakes are different from lizards primarily based on:
Feeding mechanisms
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Most snakes feed on larger animals, usually several times their own diameter
Sense organs
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Have a sensitive forked tongue, which is an organ of touch and smell
Sense of smell is well-developed
Lack movable eyelids. Eyes are covered by transparent layer. Majority have good
vision
Can’t hear; lack middle and inner ear. Can detect low frequency ground vibration
through skull bone.
Patterns of locomotion
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No legs present
Snake Evolution
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Evolved from lizards
 Most likely evolved from burrowing groups of lizards
 A few primitive snakes also burrow (worm snakes)
 Python and boas still have rudiments of hind legs that are used for courtship
Ball python
Snakes – Hunting and Feeding
Two methods to immobilize their prey
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Constrictors
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Boas, pythons, king snakes, etc.
Poisonous
How do snakes do this?
Snake Venom
Venomous snake species make up only one fifth of all snakes.
Three most important types of toxins found in snake venom:
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Neurotoxins - Affect the nervous system by seizing up the nerve centers,
causing breathing to cease
Cardiotoxins - Deteriorate the muscles of the heart, causing it to stop
often
beating
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Hemotoxins - Cause the blood vessels to rupture, resulting in widespread
internal bleeding
Some venom may also include agglutinins, which make the blood clot, or
anticoagulants, which make the blood thin. Most snake venom makes use of several
of these compounds for a deadly combined effect.
Rattlesnakes
Only poisonous snake native to California
Poison is either neurotoxic or hemolytic
(attacks blood vessels and
destroys red blood cells)
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Poison gland is modified
salivary gland
6 different species
Triangular head, narrow neck,
rattle on tail
Are called “pit vipers”
Snakes eye
Three different pupil shapes
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round pupil – hunt during the day
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vertical pupil – hunt at night
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horizontal pupil – binocular vision for judging distances between branches, etc.
Dinosaur social behavior and parental care
Vertebrate Chordates
Avis
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9,000 species
Feathers
Endodermic
Amniotic eggs with hard shell
Archaeopteryx(oldest bird)
 About 150 million years old
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Scaly skin, curving claws, teeth, feathers
Vertebrate Chordates
The Origin of Birds
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Birds probably descended from theropods, a group of small, carnivorous dinosaurs
(had
hollow bones)
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By 150 million years ago, feathered theropods had evolved into birds
Cretaceous theropod dinosaurs with putative feathers from Chinese sediments
(1998)
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Sinoauaropteryx
Filaments along its back
(may be “protofeathers”)
Flightless
Cretaceous theropod dinosaurs with putative feathers from Chinese sediments (1998)
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Caudipteryx
Contains true feathers
Flightless
Archaeopteryx, a Jurassic bird-reptile
Adaptations for Flight
Weight Reduction
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Pneumatic bones
Reduction in number of bones
No teeth
No bladder
Semi-solid urine
Male: off-season atrophy of testes
Female: has only one ovary, no oviduct
Power Production
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High metabolic rate
Rapid, efficient digestion
Large heart
Form fits function: the avian wing and feather
Flight
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Caudipteryx
Contains true feathers
Flightless
THE bills of birds corresponds to their feeding specialty
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Caudipteryx
Contains true feathers
Flightless
Phylum Chordata
Class Mammalia
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Arose on earth 180 million years ago
4,500 modern species
Mammary gland and fur (for most)
Four-chambered heart
Endothermic
Three major reproductive strategies
 Placental
 Marsupial
(e.g., koala bear, opossum)
 Monotremes
(e.g. platypus, short-nosed anteater)
Placental Mammals
Internal fertilization
Embryo develops inside the uterus
Nutrients diffuse through placental tissue
Marsupials
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Opossum, kangaroos, koalas, etc.
Develop placental tissue
Offspring are born early in its development
Monotremes
Platypus, anteater
Mammals that lay eggs (similar to reptiles)
Like other mammals, they have hair and produce milk
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No nipples
Only found in Australia and New Zealand