The Evolution of Animal Diversity

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The Evolution of Animal Diversity

• Chapter 18

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Objectives

• Comprehend and Define
• Animal characteristics
• Aspects of animal life cycle
• Hox genes
• Colonial protists
• Cambrian Explosion
• Differences between Phylums
• Distinguishing characteristics
• Differences between body plans
• Radial vs. bilateral

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What is an animal?

• Multicellular
• Heterotrophic
• Obtain nutrients by ingestion (eating food)
• Eukaryotes
• No cell walls
• Most animals are diploid and reproduce sexually

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• Blastula (early embryonic) mitotic division to
  form a hollow ball of cells
• Gastrula (embryonic) 1 side of blastula folds
  inward, develops embryo
• Ectoderm outer cell layer, develops into
• Epidermis nervous system
• Endoderm inner cell layer, develops into
• Digestive tract

Aspects of Animal Life Cycle
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• Mesoderm (in most animals -not on image) forms
  between ectoderm and endoderm
• Develops into most of the internal organs
• Larva not all animals go through larval stages
• Immature individual dissimilar from adult
• Metamorphosis major change in body form

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In animals

• Hox genes special regulatory genes that control
  the transformation of a zygote into an adult
  animal
• So far, only found in animals

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Animals probably evolved from protists that lived
as colonies of cells
Maybe happened in similar manner to this
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Cambrian explosion

• First animal fossils were from the late
  Precambrian (600,000,000 mya)
• Cambrian Explosion occurred during a span of 10
  million years
• All major animal body forms evolved
• Why did it occur?
• Increasing complex predator/prey relationships?
• Enough atmospheric oxygen finally present?
• Hox genes appeared?
• Maybe a combo of all three and/or more?

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Cambrian Explosion
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Cambrian Explosion Fossils (Burgess Shale)
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Invertebrates

• D\Invertebrates\Invertebrates.mpg

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Invert Phylum Porifera
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Invert Phylum Porifera (Sponges)

• Sponges are the simplest of all animals
• Stationary animals which are mostly found in
  marine environments
• Cylindrical sponges exhibit radial symmetry
• Body parts arranged like pieces of a pie around
  an imaginary central axis
• A simple sponge looks like a sac perforated with
  holes

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Invert Sponges
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Invert Phylum Porifera

• Body of sponge consists of 2 layers separated by
  a gelatinous region
• Choanocytes inner layer of flagellated cells
  help sweep water through the sponges body
• Amoebocytes in middle of body
• Produce skeletal fibers
• Bath sponges

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Invert Phylum Porifera

• Sponges are suspension feeders animals that
  collect food particles from water passed through
  some type of food-trapping equipment
• Sponges feed by collecting bacteria from water
  that streams through their porous bodies

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Invert Phylum Porifera

• Sponges have no nerves or muscles
• They have individual cells that can sense and
  react to changes in the environment
• Cell layers are loose federations of cells
• Sponges probably arose very early from the
  multicellular organisms that gave rise to animals

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Invert Porifera
Choanoflagellate
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Invert Phylum Cnidaria
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Invert Phylum Cnidaria

• Composed of hydras, jellyfish, sea anemones, and
  corals
• All exhibit radial symmetry
• Most are marine
• Two main body forms
• Polyp
• Medusa

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Invert Phylum Cnidaria

• Hydra common in freshwater ponds and lakes
• Have Polyp body form
• Polyp cylindrical body w/ arms (tentacles)
  projecting from one end
• Mostly stationary in water

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Invert Phylum Cnidaria

• Jellyfish marine
• Have medusa body form
• Move freely in water

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Invert Phylum Cnidaria

• Some Cnidarians have both polyp and medusa forms
  in their life cycles
• Cnidarians are carnivores that use their
  tentacles to capture prey and push them into
  their mouths
• Polyp mouth on top
• Medusa mouth on bottom
• Mouth leads to gastrovascular cavity
• Digestive compartment
• Incomplete digestive system (i.e., no anus)
• Wastes exit through the mouth

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Invert Phylum Cnidaria

• Radially symmetrical animals lack a head or any
  forward orientation
• Drift through water or on seafloor
• Besides radial symmetry, cnidocytes typify
  cnidarians
• Cnidocytes stinger cells are found on the
  surface of tentacles
• Defense and assist in capturing prey

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Invert Phylum Cnidaria
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Invert Phylum Cnidara

• Differences between Cnidaria and Porifera
• Digestive cavity
• Gastrula stage in development
• Presence of tissues nervous, muscle
• Differences between Cnidaria and rest of animals
  (besides Porifera)
• Cell layers produced during gastrulation
• Lack mesoderm

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Most animals are bilaterally symmetrical
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Bilateral Symmetry

• Bilateral symmetry animal can be divided equally
  by a single cut and has mirror-image right and
  left sides
• Anterior head
• Posterior tail
• Dorsal back
• Ventral bottom
• Lateral 2 side surfaces

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Bilateral Symmetry

• Head is prominent and houses the main sensory
  structures
• Eyes, brain, mouth
• Combined with nerves that branch throughout body,
  these structures form nervous system

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Bilateral Symmetry

• Bilaterally symmetrical animals are active
• Usually travel headfirst
• Sensory organs contact environment first and help
  animal respond appropriately
• Head end bilateral symmetry are prerequisites
  for forward movement

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Invert Phylum Platyhelminthes
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Invert Platyhelminthes

• Flatworms are leaflike or ribbonlike animals
  ranging from 1 mm 20 m!!
• Live in marine, freshwater, and damp terrestrial
  environments
• Some are parasitic
• Flatworms are bilaterally symmetrical

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Invert Platyhelminthes

• Differences between flatworms and other animals
  (besides simpler animals)
• Incomplete digestive tract
• Only space inside body is digestive cavity
• Lacks body cavity

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Invert Platyhelminthes

• Free-living flatworms ex planarian
• Non-parasitic
• Head w/ 2 large eyespots and a flap that detects
  chemicals in the water
• Dense clusters of nervous tissue form a simple
  brain w/ small nerves that branch throughout body
• Form a nervous system
• Mouth on ventral surface

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Invert Platyhelminthes
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Invert Platyhelminthes

• Flukes
• Parasites
• Males and females have suckers that attach to
  inside of blood vessels near the hosts
  intestines
• Blood flukes can cause schistosomiasis
• Widespread in Afria, Southeast Asia, and South
  America
• Afflicts 200 million people
• Causes severe abdominal pain, anemia, and
  dysentery

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Invert Platyhelminthes
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Invert Platyhelminthes

• Tapeworms
• Parasitic
• Adult tapeworms inhabit digestive tracts of
  vertebrate animals
• No digestive tract!
• Live in partially digested food
• Absorb food
• Taeniarhynchus
• Infect humans that eat infected rare beef
• Niclosamide kills adult worms

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Invert Platyhelminthes
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Body Cavities

• Most animals have body cavities
• A fluid-filled space between digestive tract and
  body wall
• Pseudocoelom a body cavity that is not
  completely lined by tissue derived from mesoderm
• Coelom a body cavity that is completely lined by
  tissue derived from mesoderm

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No Body Cavity
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Body Cavity Pseudocoelom
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Body Cavity Coelom
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Body Cavities

• Benefits
• Not solid more flexible
• Allows internal organs to grow and move
  independently of the outer body wall
• Fluid in cavity cushions internal organs
• Fluid may also circulate nutrients and oxygen,
  and aid in waste disposal

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Invert Phylum Nematoda
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Phylum Nematoda

• Cylindrical worms with a blunt head and tapered
  tail
• Have a pseudocoelom
• Have a complete digestive tract
• digestive tract in a straight tube from mouth to
  anus

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Invert Phylum Nematoda

• Animals with complete digestive tract
• Anterior regions churn and mix food with enzymes
• Posterior regions absorb nutrients and dispose
  of wastes
• Pseudocoelom also functions as a hydroskeleton

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Invert Phylum Nematoda

• Nematodes most numerous of all animals
• Are ubiquitous
• Are important decomposers in soil and on bottom
  of lakes and oceans
• Other nematodes are parasites

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Invert Phylum Mollusca
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Invert Phylum Mollusca

• Ex snails, slugs, oysters, clams, octopuses,
  squid, and more
• Have a soft body protected by a hard shell
• All mollusks have
• A muscular foot
• Visceral mass containing most internal organs
• Mantle a fold of tissue that drapes over the
  visceral mass and produces the shell

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Invert Phylum Mollusca

• Mollusks also have
• true coelom
• circulatory system
• Distributes nutrients and oxygen throughout the
  body

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Invert Phylum Mollusca
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Invert Phylum MolluscaClass Gastropoda
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Invert Phylum MolluscaClass Gastropoda

• Largest group of mollusks
• Found in fresh salt water, and terrestrial
  environments
• Only mollusks that live on land
• Most are protected by a single, spiraled shell
  into which the animal can retreat when threatened
• No gills, instead, lining of mantle cavity
  functions as a lung

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Invert Phylum MolluscaClass Cephalopoda
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Invert Phylum MolluscaClass Cephalopoda

• Built for speed and agility
• Except for the chambered nautilus, cephalopods
  have small internal shells (squids) or none at
  all (octopuses)
• Marine predators
• Squid have a large complex brain and complex eyes
• Octopuses are the largest and most complicated of
  any invertebrate

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Many animals have a segmented body
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Many animals have a segmented body

• Segmentation is a major feature of many animals
• Subdivision of the body along its length into a
  series of repeated parts
• Allows great flexibility and mobility
• Probably evolved as an adaptation for movement

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Invert Phylum Annelida
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Invert Phylum Annelida

• Segmented body
• Body parts all similar except head tail
• Live in sea, most freshwater habitats, and in
  damp soil
• Most are bottom-dwelling scavengers

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Invert Phylum Annelida Class Oligochaeta
(Earthworms)
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Invert Phylum AnnelidaClass Oligochaeta
(Earthworms)

• Eat its way through soil, extracting nutrients as
  soil passes through its digestive tube
• Eliminates castings (feces) through anus
• Earthworms aerate soil and contribute to nutrient
  cycling

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Invert AnnelidaClass Hirudinea (Leeches)
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Invert Phylum Annelida Class Hirudinea (Leeches)

• Most are free-living carnivores that eat small
  invertebrates
• Some are parasitic
• Majority live in fresh water, but a few live in
  terrestrial environments (tropics)

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Invert Phylum Arthropoda
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Invert Phylum Arthropoda

• Most numerous and widespread of all animals
• Arthropod individuals billion billion!!
• Have jointed appendages
• Have an exoskeleton, a hard external shell
  composed of protein and chitin
• Protects animals thick around head
• Provides points of attachment for muscles to move
  appendages

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Invert Phylum Arthropoda

• Arthropods molt or shed their old exoskeletons
  and secrete a larger one in order to grow
• Members of Phylum Annelida have similar segments
  throughout their body BUT,
• Arthropods have several distinct segments

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Invert Phylum Arthropoda
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Invert Phylum ArthropodaClass Arachnida
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Invert Phylum Arthropoda Class Arachnida

• Comprised of scorpions, spiders, ticks, and mites
• Most live on land
• Mites a ubiquitous scavenger in homes
• Thousands can live in a few square centimeters of
  carpet or in dust balls
• Many people are allergic to them

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Invert Phylum ArthropodaCrustaceans
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Invert Phylum ArthropodaCrustaceans

• Lobsters, crayfish, crabs, shrimps, and barnacles
  
• Majority are aquatic

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Invert Phylum Arthropoda Millipedes and
Centipedes
Class Diplopoda
Class Chilopoda
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Invert Phylum Arthropoda Millipedes and
Centipedes

• Superficially resemble annelids, BUT their
  jointed legs identify them as arthropods
• Millipedes are wormlike terrestrial animals that
  eat decaying plant matter
• Have 2 pairs of short legs per body segment
• Centipedes are terrestrial carnivores that have a
  pair of poison claws
• Have 1 pair of long legs per body segment

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Invert Phylum ArthropodaClass Insecta
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Invert Phylum Arthropoda Class Insecta

• Total number of insect species is greater than
  the total of all other species combined
• Prominent on land for past 400 million years
• Terrestrial, fresh water, and flying insects
• Few marine insects where crustaceans are dominant
• Important pollinators

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Invert Phylum Arthropoda Class Insecta

• Many insects undergo metamorphosis
• Incomplete metamorphosis young resemble adults
  but are smaller with different body proportions
• Complete metamorphosis have larval stages

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Invert Phylum Echinodermata
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Invert Phylum Echinodermata

• Sea stars, sand dollars, and sea urchins
• All marine
• Very different evolutionary branch than mollusks,
  annelids, and arthropods
• Lack body segments
• Most are radially symmetrical

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Invert Phylum Echinodermata

• If most are radially symmetrical, why arent they
  closely related to animals that are radially
  symmetrical?
• Bilateral larval stage
• Spiny skin are from hard spines or plates
  embedded under the skin forming an endoskeleton
• Water vascular system unique to Echinodermata
• Network of water-filled canals that branch into
  extensions called tube feet
• Locomotion, feeding, gas exchange

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Phylum Chordata

• 4 distinguishing features in embryos and in some
  adults
• Dorsal hollow nerve cord
• Notochord
• Flexible, supportive, longitudinal rod located
  between the digestive tract and the nerve cord
• pharyngeal slits endostyles
• Gill structures in the pharynx, the region of the
  digestive tube just behind the mouth
• Post-anal tail
• A tail posterior to the anus

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Phylum Chordata invertebrates the Tunicates
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Phylum Chordata invertebrates the Tunicates

• Stationary
• Adhere to rocks and boats, common on coral reefs
• Suspension feeders
• Larva have all 4 features
• Adults have no trace of a notochord, nerve cord,
  or tail
• But have prominent pharyngeal slits

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Phylum Chordata invertebrates the Lancelets
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Phylum Chordata invertebrates the Lancelets

• Live in marine sands
• Suspension feeders
• Have 4 chordate features
• Have segmented muscles
• Molecular evidence indicates that lancelets are
  the closest living invertebrate chordate
  relatives of vertebrates

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Phylum Chordata The Vertebrates

• Comprise most of Phylum Chordata
• Have
• Skull
• Encloses brain
• Backbone composed of vertebrae
• Encloses nerve cord
• Most have skeletal parts supporting appendages
• Most have a hinged jaw
• Endoskeleton made of flexible cartilage or hard
  bone and cartilage
• can grow with the animal

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Phylum Chordata VertebratesAgnathans -lampreys

• Primitive vert without jaws
• More closely related to extinct jawless vert than
  other living vert

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Phylum Chordata Vertebrates
How was the advent of the hinged jaw beneficial
to vertebrates?
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Phylum Chordata Vertebrates Class Chondrichthyes
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Phylum Chordata Vertebrates -Fish

• First jawed vertebrates
• Gills to extract oxygen from water
• Paired forefins and hindfins to maneuver in water

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Phylum Chordata Vertebrates Class Chondrichthyes

• Ex sharks, rays, and skates
• Cartilaginous fish
• Flexible skeleton made of cartilage
• Suspension feeders and predators
• Sharks have a lateral line system
• Row of sensory organs running along each side
  that are sensitive to changes in water pressure

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Phylum Chordata Vertebrates Class Osteichthyes
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Phylum Chordata Vertebrates Class Osteichthyes

• Bony fish have a skeleton reinforced with a hard
  matrix of calcium phosphate
• Have flattened scales covering their skin and
  mucous coating that reduces drag
• Also have a lateral line system
• Swim bladder gas-filled sac that helps keep them
  buoyant

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Phylum Chordata Vertebrates Class Osteichthyes
lung fish
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Phylum Chordata Vertebrates Class Amphibia
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Phylum Chordata Vertebrates Class Amphibia

• Ex frogs, toads, and salamanders
• First terrestrial vertebrates
• Part of life cycle is spent in the water
• Eggs laid in water which develops into a
• Tadpole gills, lateral line, finned tail
• Undergo metamorphosis into adult and lose tadpole
  features
• Rapid decline of amphibians

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Transition from fish to amphibian

• Transition occurred over 400 to 350 mya
• Aconthostega
• Bone that supports gills
• Also lungs
• Four appendages and other similar skeletal
  elements of amphibians, etc.

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Phylum Chordata Vertebrates Class Reptilia
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Phylum Chordata Vertebrates Class Reptilia

• Lizards, snakes, turtles, crocodiles, alligators
  extinct dinosaurs
• Have several adaptations for terrestrial living
• Skin covered with waterproof scales
• Keeps skin from drying out
• Protected eggs that retain water
• Amniotic egg embryo develops in protective,
  fluid-filled sac called amnion

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Phylum Chordata Vertebrates Class Reptilia

• Reptiles are Ectothermic absorb external heat
  rather than generating their own via metabolism

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Phylum Chordata Vertebrates Class Aves
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Phylum Chordata Vertebrates Class Aves

• Strong fossil evidences indicates that birds
  evolved from 2-legged dinosaurs 150-200 mya
• Inherited from reptiles amniotic eggs, scales on
  legs, body form, feathers
• Body adapted for flight
• Light body, flight feathers, high metabolism
  (modern birds are endothermic), acute senses,
  powerful flight muscles

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Phylum Chordata Vertebrates Class Mammalia
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Phylum Chordata Vertebrates Class Mammalia

• Endothermic warm, constant body temperature
  generated by metabolism
• Hair to insulate body and help maintain body temp
• Mammary glands produce milk to nourish young
• Monotreme (Ex Platypus) only egg-laying mammal

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Phylum Chordata Vertebrates Class Mammalia

• Most mammals are born
• Embryos nurtured inside mother by placenta
• Consists of embryonic and maternal tissues
• Maternal blood flows close to embryonic blood
  system in placenta
• Marsupials have a brief gestation period
• Give birth to tiny embryonic offspring that
  complete development while attached to mothers
  nipples

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Phylum Chordata Vertebrates Class Mammalia

• Eutherians (placentals) comprise 95 of living
  mammals
• Intimate and long-lasting association b/w mother
  and developing young

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