Animal Evolution

1
Animal Evolution The Invertebrates
2
Comparing Key Groups

• Evolutionary trends toward
• Greater size
• Compartmentalization (division of labor among
  cells, tissues, and organs)
• Integration of specialized activities that keep
  the organism alive

3
Body Symmetry Radial and Bilateral

• Most animals are bilateral

4
Body Organization

• Cephalization
• Sensory cells concentrated at the head
• Segmentation
• Repetition of body units, front-to-back

5
Body Cavities

• Most bilateral animals have a coelom and a
  complete gut

6
Key Concepts INTRODUCING THE ANIMALS

• Animals
• Multicelled heterotrophs (ingest other organisms)
  
• Grow and develop through a series of stages
• Actively move about during all or part of life
  cycle
• Cells of most animals form tissues and
  extracellular matrixes

7
Sponges (Phylum Porifera)

• Sponges
• No symmetry, tissues, or organs
• Flattened cells line the body wall (many pores
  spikes of silica and/or proteins)
• Filter feeders (flagellated collar cells absorb
  food amoeboid cells digest and distribute it)
• Zygote develops into free-living larva

8
Sponges
9
Cnidarians (Phylum Cnidaria)

• Jellyfishes, corals, and sea anemones
• Radial, tentacled carnivores
• Gastrovascular cavity (respiration and digestion)
• True epithelial tissues with a jellylike matrix
  in between
• Simple nervous system

10
Cnidarian Body Plans
11
Unique Cnidarian Weapons

• Nematocysts
• Used to capture prey and for defense

12
Cnidarian Predators
13
Cnidarian Life Cycles
14
Flatworms (Phylum Platyhelminthes)

• Free-living turbellarians (planarians), parasitic
  tapeworms and flukes
• Simplest animals with organ systems
• Paired nerve cords

15
Parasite Life Cycle Blood Fluke
16
Parasite Life Cycle Tapeworm
17
Annelids

• Segmented worms (earthworms, polychaetes) and
  leeches
• Closed circulatory system
• Digestive and excretory systems
• Nervous system, ganglia in each segment
• Muscles and fluid in chambers act as a
  hydrostatic skeleton

18
head end
secretory organ
19
Polychaete
20
Mollusks (Phylum Mollusca)

• Including gastropods (snails), bivalves
  (scallops), chitons, nudibranchs, cephalopods
• 100,000 named species

21
Aquatic Snail Body Plan
22
Cephalopods

• The fastest (squids), largest (giant squids), and
  smartest (octopuses) invertebrates
• Have a mantle
• Sheetlike part of the body mass, draped back on
  itself

23
Cephalopods
24
Cuttlefish Body Plan
25
Roundworms (Phylum Nematoda)

• More than 22,000 kinds of roundworms
• Free-living decomposers or parasites
• Some agricultural pests and human parasites
• Cylindrical body with bilateral features
• A complete gut
• Organ systems in a false coelom

26
Parasitic Roundworms
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Key Concepts BILATERAL INVERTEBRATES

• Most animals show bilateral symmetry
• Bilateral animals have tissues, organs, and organ
  systems
• All adult tissues arise from two or three simple
  layers that form in early embryos

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Simple Arthropods

• Trilobite, millipede, centipede

29
Arthropod Characteristics

• Key arthropod adaptations
• Hardened exoskeleton
• Jointed appendages
• Specialized and fused segments (wings)
• Efficient respiratory and sensory structures
  (eyes, antennae)

30
Chelicerates

• Horseshoe crabs and arachnids (spiders,
  scorpions, ticks, and mites)
• Predators, parasites, or scavengers

31
Crustaceans

• Mostly marine crustaceans (crabs, lobsters,
  barnacles, krill, and copepods)

32
Insect Diversity
33
Unwelcome Arthropods

• Spiders, ticks, and mosquitoes

34
Echinoderms

• Sea stars, sea urchins, sea cucumbers, etc.
• Exoskeleton with spines, spicules, or plates of
  calcium carbonate
• Water-vascular system with tube feet
• Adults are radial, but bilateral traits appear in
  larval stages

35
Echinoderms Spiny-Skinned
36
Fig. 23.34, p.381
37
Animal Evolution The Vertebrates
38
Chordate Heritage

• Four features define chordates
• A notochord
• A dorsal hollow nerve cord
• A pharynx with gill slits
• A tail extending past the anus
• All features form in embryos
• May or may not persist in adults

39
Invertebrate Chordates

• Tunicates and lancelets (marine filter-feeders)

40
Lancelet Body Plan
41
Craniates

• Chordates with a braincase of cartilage or bone
• Hagfish (jawless fish) Simplest modern craniate

42
Vertebrate Evolution

• Key innovations laid the foundation for adaptive
  radiations of vertebrates
• Vertebral column of cartilaginous or bony
  segments
• Jaws evolved in predatory fishes
• Gills evolved in water, then lungs for dry land
• Paired fins were a starting point for other limbs
• Gill-Supporting Structures

43
Key Concepts TRENDS AMONG VERTEBRATES

• In some vertebrate lineages, a backbone replaced
  the notochord as the partner of muscles used in
  motion
• Jaws evolved, sparking the evolution of novel
  sensory organs and brain expansions
• On land, lungs replaced gills, and more efficient
  blood circulation enhanced gas exchange
• Fleshy fins with skeletal supports evolved into
  limbs, now typical of vertebrates on land

44
Jawed Fishes and Tetrapods

• Jawed fishes
• Cartilaginous fishes (sharks and rays)
• Bony fishes
• Body plans adapted to life in water
• Streamlined shape reduces drag
• Swim bladder (in bony fishes) adjusts buoyancy

45
Cartilaginous Fishes
46
Bony Fishes

• The most diverse vertebrates
• Lungfishes
• Lobe-finned fishes (coelacanth)
• Ray-finned fishes

47
Early Lineages

• Coelacanth, lungfish, and Devonian tetrapod

48
Amphibians

• Frogs, toads, and salamanders
• Carnivorous vertebrates
• Adapted to life on land (lungs, 3-chambered
  heart)
• Nearly all return to the water to reproduce

49
Amphibian Evolution
50
Amniotes

• First vertebrates able to complete their life
  cycle on dry land
• Water-conserving skin and kidneys
• Amniote eggs (four membranes)
• Active life-styles

51
Dinosaur Extinctions

• K-T asteroid impact hypothesis
• A huge asteroid impact caused extinction of last
  dinosaurs spared earliest birds and mammals

52
Modern Reptiles

• Major Groups
• Turtles (shell attached to skeleton)
• Lizards (the most diverse reptiles)
• Snakes (limbless)
• Crocodilians (closest relatives of birds)

53
Fig. 24.17, p.397
54
Fig. 24.17, p.397
55
Fig. 24.17, p.397
56
Reptile Characteristics

• General characteristics
• Live on land or in water
• Cold-blooded
• Have a cloaca (opening for wastes and
  reproduction)
• Eggs are fertilized in the body, usually laid on
  land

57
hindbrain, midbrain, forebrain
spinal cord
vertebral column
olfactory lobe (sense of smell)
kidney (control of water, solute levels in
internal environment)
gonad
snout
unmatched rows of teeth on upper and lower jaws
cloaca
stomach
lung
heart
liver
intestine
esophagus
Fig. 24.16, p.396
58
Birds

• Birds are the only modern animals with feathers

59
Bird Eggs

• Birds are warm-blooded amniotes

60
Adaptations for Flight and Migration

• Feathers, lightweight bones, and highly efficient
  respiratory and circulatory systems

61
Mammals

• Animals with hair, females that nourish young
  with milk from mammary glands, a single lower
  jawbone and four kinds of teeth

62
Modern Mammals

• Three major lineages
• Egg-laying mammals (monotremes)
• Pouched mammals (marsupials)
• Placental mammals, the most diverse and
  widespread mammals

63
Three Major Lineages
64
Placental Mammals
65
Primates
66
Primate Evolution

• Key trends
• Better daytime vision
• Upright walking (bipedalism)
• More refined hand movements
• Smaller teeth
• Bigger brains
• Social complexity (extended parental care
  culture evolved in some lineages)

67
The Foramen Magnum

• Four-legged walkers versus upright walkers

68
Emergence of Early Humans

• Hominoids and hominids originated in Africa

69
Australopiths Upright Walking
70
Early Humans

• Humans (Homo) arose 2 million years ago
• H. habilis was an early toolmaking species
• H. erectus dispersed into Europe and Asia

71
Emergence of Modern Humans

• Extinct Neandertals and modern humans are close
  relatives with distinct gene pools
• Modern H. sapiens evolved 195,000 years ago

72
Dispersal of Homo sapiens

• Based on fossils and studies of genetic markers