The Evolution of Animal Diversity

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Chapter 18
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• The Evolution of Animal Diversity

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• What Am I?
• Of some 1.5 million species of organisms known to
  science
• Over two-thirds are animals
• Humans have a long history of studying animal
  diversity
• But classifying an animal isnt always easy

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• Imagine you were the first person to encounter
  the animal pictured here
• With all of its varying characteristics, what
  would you think it is?

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• Biologists often encounter classification
  problems
• When evolution creates organisms with similar
  characteristics

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ANIMAL EVOLUTION AND DIVERSITY

• What is an animal?
• Animals are eukaryotic, multicellular
  heterotrophs
• That ingest their food

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• Animal development
• May include a blastula, gastrula, and larval stage

Key
Haploid (n) Diploid (2n)
Sperm
2
1
Egg
Meiosis
Zygote(fertilized egg)
3
Eight-cell stage
Adult
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Metamorphosis
4
Blastula(cross section)
Digestive tract
Ectoderm
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Larva
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Early gastrula(cross section)
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Endoderm
Futuremesoderm
Figure 18.1B
Internal sac
Later gastrula(cross section)
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• The ancestor of animals was probably a colonial,
  flagellated protist
• Cells in these protists
• Gradually became more specialized and layered

Somaticcells
Digestive cavity
Reproductivecells
1 Colonial protist, an aggregate
of identical cells
2 Hollow sphere of unspecialized
cells (shown in cross section)
3 Beginning of cell specialization
(cross section)
4 Infolding (cross section)
5 Gastrula-like proto-animal
(cross section)
Figure 18.2A
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• Animal diversity exploded during the Cambrian
  period

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• Animals can be characterized by basic features of
  their body plan
• Animal body plans may vary in symmetry

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• Vary in body cavity

Figure 18.3BD
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• Development as either protostomes or
  deuterostomes
• Together these animals show bilateral symmetry
  and three germ layers
• Distinction between each is found in embryonic
  development

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• The body plans of animals can be used to build
  phylogenetic trees
• One hypothesis of animal phylogeny is based on
  morphological comparisons

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Invertebrates
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INVERTEBRATES

• Sponges have a relatively simple, porous body
• Sponges, phylum Porifera
• Are the simplest animals and have no true tissues

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• Flagellated choanocytes
• Filter food from the water passing through the
  porous body

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• Cnidarians are radial animals with tentacles and
  stinging cells
• Cnidarians, phylum Cnidaria
• Have true tissues and radial symmetry

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• Their two body forms are
• Polyps, such as hydra
• Medusae, the jellies

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• They have a gastrovascular cavity
• And cnidocytes on tentacles that sting prey

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• Flatworms are the simplest bilateral animals
• Flatworms, phylum Platyhelminthes
• Are bilateral animals with no body cavity

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• A planarian has a gastrovascular cavity
• And a simple ner vous system

Planaria
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• Flukes and tapeworms
• Are parasitic flatworms with complex life cycles

Figure 18.7B
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• Nematodes have a pseudocoelom and a complete
  digestive tract
• Nematodes, phylum Nematoda
• Have a pseudocoelom and a complete digestive
  tract
• Are covered by a protective cuticle

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• Many nematodes are free-living
• And others are plant or animal parasites

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• Diverse molluscs are variations on a common body
  plan
• All molluscs have a muscular foot and a mantle
• Which may secrete a shell that encloses the
  visceral mass
• Many mollusks
• Feed with a rasping radula

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• Gastropods
• Gastropods are the largest group of molluscs
• And include the snails and slugs

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• Bivalves
• The bivalves have shells divided into two halves
• And include clams, oysters, mussels, and scallops

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• Cephalopods
• Cephalopods are adapted to be agile predators
• And include squids, cuttlefish and octopuses

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• Annelids are segmented worms
• The segmented bodies of phylum Annelida
• Give them added mobility for swimming and
  burrowing

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• Ear thworms and Their Relatives
• Ear thworms
• Eat their way through soil
• Have a closed circulatory system

Figure 18.10A
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• Polychaetes
• Form the largest group of annelids
• Search for prey on the seafloor or live in tubes
  and filter food particles

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• Leeches
• Most leeches
• Are free-living carnivores, but some suck blood

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• Ar thropods are segmented animals with jointed
  appendages and an exoskeleton
• The diversity and success of ar thropods is
  largely related to their segmentation,
  exoskeleton, and jointed appendages

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• Chelicerates
• Chelicerates include
• Horseshoe crabs
• Arachnids, such as spiders, scorpions, mites, and
  ticks

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• Millipedes and Centipedes
• Millipedes and centipedes
• Are identified by the number of jointed legs per
  body segment

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• Crustaceans
• The crustaceans
• Are nearly all aquatic
• Include crabs, shrimps, and barnacles

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• Insects are the most diverse group of organisms
• Insects have a three-par t body consisting of
• Head, thorax, and abdomen
• Three sets of legs
• Wings (most, but not all insects)

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• Many insects undergo
• Incomplete or complete metamorphosis

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• A. Order Or thoptera
• The order orthoptera includes
• Grasshoppers, crickets, katydids, and locusts

Figure 18.12A
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• B. Order Odonata
• The order odonata includes
• Dragonflies and damselflies

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• C. Order Hemiptera
• The order hemiptera includes
• Bedbugs, plant bugs, stinkbugs, and water striders

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• D. Order Coleoptera
• The order coleoptera includes
• Beetles

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• E. Order Lepidoptera
• The order lepidoptera includes
• Moths and butter flies

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• F. Order Diptera
• The order Diptera includes
• Flies, fruit flies, houseflies, gnats, and
  mosquitoes

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• G. Order Hymenoptera
• The order hymenoptera includes
• Ants, bees, and wasps

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• Echinoderms have spiny skin, an endoskeleton, and
  a water vascular system for movement
• Echinoderms, phylum Echinodermata
• Includes organisms such as sea stars and sea
  urchins
• Are radially symmetrical as adults

Tube foot
Spine
Figure 18.13B, C
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• The water vascular system
• Has suction cuplike tube feet used for
  respiration and locomotion

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• Our own phylum, Chordata, is distinguished by
  four features

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• The simplest chordates are tunicates and
  lancelets
• Marine inver tebrates that use their phar yngeal
  slits for suspension feeding

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VERTEBRATES

• Derived characters define the major clades of
  chordates
• A chordate phylogenetic tree
• Is based on a sequence of derived characters

Figure 18.15
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• Most chordates are ver tebrates
• With a head and a backbone made of ver tebrae

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• Lampreys are ver tebrates that lack hinged jaws
• Lampreys lack hinged jaws and paired fins

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• Most ver tebrates have hinged jaws
• Which may have evolved from skeletal suppor ts
  of the gill slits

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• Jawed vertebrates with gills and paired fins
  include sharks, ray-finned fishes, and lobe-fins
• Three lineages of jawed vertebrates with gills
  and paired fins
• Are commonly called fishes

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• Chondrichthyans
• Chondrichthyans
• Have a flexible skeleton made of car tilage
• Include sharks and rays

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• Ray-finned Fishes (e.g. Atlantic herring, Ocean
  sunfish)
• The ray-finned fishes have
• A skeleton reinforced with a hard matrix of
  calcium phosphate
• Operculi that move water over the gills
• A buoyant swim bladder

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• Lobe-fins (e.g. coelacanths, lungfish)
• The lobe-fin fishes
• Have muscular fins suppor ted by bones

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• Amphibians were the first tetrapodsver tebrates
  with two pairs of limbs
• Amphibians
• Were the first tetrapods with limbs allowing
  movement on land

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• Include frogs, toads, salamanders, and caecilians

• Most amphibian embr yos and lar vae still must
  develop in water

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• Reptiles are amniotestetrapods with a
  terrestrially adapted egg
• Terrestrial adaptations of reptiles include
• Waterproof scales
• A shelled, amniotic egg

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• Living reptiles other than birds are ectothermic

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• Dinosaurs, the most diverse reptiles to inhabit
  land
• Included some of the largest animals ever to
  inhabit land
• May have been endothermic, producing their own
  body heat

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• Birds are feathered reptiles with adaptations for
  flight
• Birds evolved from
• A lineage of small, two-legged dinosaurs called
  theropods

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• Birds are reptiles that have
• Wings, feathers, endothermic metabolism, and many
  other adaptations related to flight

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• Flight ability is typical of birds
• But there are a few flightless species

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• Mammals are amniotes that have hair and produce
  milk
• Mammals are endothermic amniotes with
• Hair, which insulates their bodies
• Mammary glands, which produce milk

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Mammals
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• Monotremes lay eggs

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• Monotremes lay eggs

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• The embryos of marsupials and eutherians are
  nurtured by the placenta within the uterus
• Marsupial offspring complete development attached
  to the mothers nipple, usually inside a pouch

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• Eutherians, placental mammals
• Complete development before bir th

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ANIMAL PHYLOGENY AND DIVERSITY REVISITED

• An animal phylogenetic tree is a work in
  progress
• Molecular-based phylogenetic trees
• Distinguish two protostome clades the
  lophotrochozoans and the ecdysozoans

Molluscs
Annelids
Sponges
Chordates
Arthropods
Flatworms
Nematodes
Cnidarians
Echinoderms
Deuterostomes
Ecdysozoans
Lophotrochozoans
Bilaterians
Radial symmetry
Bilateral symmetry
Eumetazoans
No true tissues
True tissues
Figure 18.22
Ancestral colonial protist
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CONNECTION

• Humans threaten animal diversity by introducing
  non-native species
• Introduced species
• Are threatening Australias native animals