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The Evolution of Animals Figures 17.1 – 17.3

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1 The Evolution of Animals Figures 17.1 – 17.3
CHAPTER 17 The Evolution of Animals Figures 17.1 – 17.3

2 Zoologists estimate that about a billion billion (1018) individual arthropods populate the Earth
Tapeworms can reach lengths of 20 meters in the human intestine

3 The blue whale, an endangered species that grows to lengths of nearly 30 meters, is the largest animal that has ever existed A reptile can survive on less than 10% of the calories required by a mammal of equivalent size

The incredible diversity of animals Arose through hundreds of millions of years of evolution Can be quickly threatened

5 The Australian quoll Is a catlike creature that preys on many small animals, such as toads Figure 17.1a

6 A non-native toad Was introduced from South America in 1935 to fight beetles in sugarcane fields Caused considerable damage to the ecosystem Figure 17.1b

Animal life began in the Precambrian seas with the evolution of multicellular creatures that ate other organisms

8 What Is an Animal? Animals
Are eukaryotic, multicellular, heterotrophic organisms that obtain nutrients by ingestion Digest their food within their bodies Figure 17.2

9 Most animals reproduce sexually and then proceed through a series of developmental stages
Haploid Sperm Egg 1 2 Meiosis Fertilization Zygote (fertilized egg) Adult 3 Diploid Blastula (cross section) 7 Metamorphosis Digestive tract Outer cell layer (ectoderm) 4 Primitive gut 6 5 Early gastrula Larva Inner cell layer (endoderm) Later gastrula Figure 17.3 Opening

10 Most animals have muscle cells and nerve cells that control the muscles

11 Early Animals and the Cambrian Explosion
Animals probably evolved from a colonial protist that lived in the Precambrian seas Digestive cavity Reproductive cells Somatic cells 1 Early colony of protists (aggregate of identical cells) 2 Hollow sphere (shown in cross section) 3 Beginning of cell specialization 4 Infolding 5 Gastrula-like “proto-animal” Figure 17.4

12 At the beginning of the Cambrian period, 545 million years ago, animals underwent a rapid diversification Figure 17.5

13 What ignited the Cambrian explosion?
Many hypotheses exist

14 Animal Phylogeny To reconstruct the evolutionary history of animal phyla, researchers must depend on clues from comparative anatomy and embryology

15 Four key evolutionary branch points have been hypothesized

16 4 3 2 1 Coelom from digestive tube Pseudocoelom True coelom
Sponges Cnidarians Flatworms Roundworms Mollusks Annelids Arthropods Echinoderms Chordates Coelom from cell masses Coelom from digestive tube 4 Pseudocoelom True coelom No body cavity 3 Body cavities Radial symmetry Bilateral symmetry 2 True tissues 1 Multicellularity Figure 17.6

17 The first branch point is defined by the presence of true tissues

18 (b) Bilateral symmetry
The second major evolutionary split is based partly on body symmetry (a) Radial symmetry (b) Bilateral symmetry Figure 17.7

19 Third, the evolution of body cavities led to more complex animals

20 A body cavity Body covering (from ectoderm) Tissue-filled region (from mesoderm) Is a fluid-filled space separating the digestive tract from the outer body wall May be a pseudocoelom or a true coelom Digestive tract (from endoderm) (a) No body cavity (e.g., flatworm) Pseudocoelom Body covering (from ectoderm) Digestive tract (from endoderm) Muscle layer (from mesoderm) (b) Pseudocoelom (e.g., roundworm) Coelom Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Digestive tract (from endoderm) Mesentery (c) True coelom (e.g., annelid) Figure 17.8

21 Fourth, among animals with a true coelom, there are two main evolutionary branches, which differ in embryonic development

Invertebrates Are animals without backbones Represent 95% of the animal kingdom

23 Sponges Phylum Porifera
Includes sessile animals once believed to be plants Lack true tissues Figure 17.9

24 The body of a sponge Resembles a sac perforated with holes
Draws water into a central cavity, where food is collected

25 Choanocyte in contact with an amoebocyte
Pores Water flow Skeleton fiber Central cavity Choanocyte Flagella Amoebocyte Figure 17.10

26 Cnidarians Phylum Cnidaria
Is characterized by organisms with radial symmetry and tentacles with stinging cells

27 The basic body plan of a cnidarian
Is a sac with a gastrovascular cavity Has two variations: the sessile polyp and the floating medusa Mouth/anus Tentacle Gastrovascular cavity Tentacle Mouth/anus Polyp form Medusa form Figure 17.11

28 Examples of polyps are Hydras, sea anemones, and coral animals
Figure 17.12

29 The organisms we call jellies are medusas

30 Cnidarians are carnivores that use tentacles armed with cnidocytes, or “stinging cells,” to capture prey Coiled thread Tentacle Capsule “Trigger” Cnidocyte Discharge of thread Prey Figure 17.13

31 Phylum Platyhelminthes
Flatworms Phylum Platyhelminthes Is represented by the simplest bilateral animals Includes free-living forms such as planarians Digestive tract (gastrovascular cavity) Nerve cords Mouth Eyespots Nervous tissue clusters Figure 17.14

32 Some flatworms are parasitic
Head Blood flukes are an example Tapeworms parasitize many vertebrates, including humans Reproductive structures Hooks Sucker Figure 17.15

33 Roundworms Phylum Nematoda
Includes the most diverse and widespread of all animals Occurs in aquatic and moist terrestrial habitats Figure 17.16

34 Roundworms exhibit an important evolutionary adaptation, a digestive tube with two openings, a mouth and an anus A complete digestive tract can process food and absorb nutrients efficiently

35 Mollusks Phylum Mollusca
Is represented by soft-bodied animals, but most are protected by a hard shell Includes snails, slugs, clams, octopuses, and squids, to name a few

36 The body of a mollusk has three main parts: a muscular foot, a visceral mass, and a mantle
Reproductive organs Coelom Mantle Kidney Heart Digestive tract Mantle cavity Radula Shell Radula Anus Gill Mouth Nerve cords Foot Mouth Figure 17.17

37 The three major classes of mollusks are
Gastropods, which are protected by a single, spiraled shell Figure 17.18a

38 Bivalves, protected by shells divided into two halves
Figure 17.18b

39 Cephalopods, which may or may not have a shell
Figure 17.18c

40 Annelids Phylum Annelida Includes worms with body segmentation Anus
Brain Main heart Coelom Digestive tract Segment walls Mouth Accessory hearts Nerve cord Blood vessels Excretory organ Figure 17.19

41 There are three main classes of annelids
Earthworms, which eat their way through soil Figure 17.20a

42 Polychaetes, which burrow in the sea floor
Figure 17.20b

43 Leeches, some of which are parasitic
Figure 17.20c

44 Arthropods Phylum Arthropoda
Contains organisms named for their jointed appendages Includes crustaceans, arachnids, and insects

45 General Characteristics of Arthropods
Arthropods are segmented animals with specialized segments and appendages Cephalothorax Abdomen Thorax Antennae (sensory reception) Head Swimming appendages Walking legs Pincer (defense) Mouthparts (feeding) Figure 17.21

46 The body of an arthropod is completely covered by an exoskeleton

47 There are four main groups of arthropods
Arthropod Diversity There are four main groups of arthropods Arachnids, such as spiders, scorpions, ticks, and mites Figure 17.22

48 Crustaceans, such as crabs, lobsters, crayfish, shrimps, and barnacles
Figure 17.23

49 Millipedes and centipedes
Figure 17.24

50 Insects, most of which have a three-part body
Head Thorax Abdomen Hawk moth Antenna Forewing Eye Mosquito Paper wasp Mouthparts Hindwing Grasshopper Damselfly Water strider Ground beetle Figure 17.25

51 Many insects undergo metamorphosis in their development
(a) Larva (caterpillar) (b) Pupa (c) Pupa (d) Emerging adult (e) Adult Figure 17.26

52 Echinoderms Phylum Echinodermata
Is named for the spiny surfaces of the organisms Includes sea stars, sand dollars, sea urchins, and sea cucumbers Figure 17.27

53 Echinoderms Are all marine Lack body segments
Usually have an endoskeleton Have a water vascular system that facilitates gas exchange and waste disposal

Vertebrates Are represented by mammals, birds, reptiles, amphibians, and fishes Have unique features, including the cranium and backbone Figure 17.28

55 Characteristics of Chordates
Phylum Chordata Includes the subphylum of vertebrates

56 Other subphyla include the lancelets and tunicates, which share four key chordate characteristics
Figure 17.29

57 The four chordate hallmarks are
A dorsal, hollow nerve cord A notochord Pharyngeal slits A post-anal tail

58 Dorsal, hollow nerve cord
Notochord Brain Muscle segments Mouth Anus Pharyngeal slits Post-anal tail Figure 17.30

59 An overview of chordate and vertebrate evolution

60 Lungs or lung derivatives
Chordates Vertebrates Tetrapods Periods Amniotes Eras Cenozoic Tunicates Tertiary Aves (birds) Lancelets Mammalia (mammals) Reptilia (reptiles) Cretaceous Amphibia (frogs and salamanders) Mesozoic Agnatha (jawless vertebrates, such as lampreys) Osteichthyes (bony fishes) Feathers Jurassic Chondrichthyes (sharks and rays) Triassic Permian Hair Carboniferous Amniotic egg Devonian Paleozoic Legs Silurian Lungs or lung derivatives Ordovician Jaws Cambrian Vertebrae Precambrian Ancestral chordate Figure 17.31

61 Fishes The first vertebrates probably evolved during the early Cambrian period, about 540 million years ago

62 These early vertebrates, the agnathans, lacked jaws
Agnathans are represented today by lampreys

63 The two major groups of living fishes are the classes
Chondrichthyes Osteichthyes

64 Cartilaginous fishes have a flexible skeleton made of cartilage
Sharks have a lateral line system sensitive to vibrations in the water Figure 17.32a

65 Bony fishes Have a skeleton reinforced by hard calcium salts
Have a lateral line system, a keen sense of smell, and excellent eyesight Figure 17.32b

66 Most bony fishes are ray-finned fishes
A second evolutionary branch includes lungfishes and lobe-finned fishes

67 Members of the class Amphibia
Amphibians Members of the class Amphibia Exhibit a mixture of aquatic and terrestrial adaptations Usually need water to reproduce Figure 17.33

68 Amphibians Were the first vertebrates to colonize land
Descended from fishes that had lungs and fins with muscles Lobe-finned fish Early amphibian Figure 17.34

69 Terrestrial vertebrates are collectively called tetrapods, which means “four legs”

70 Reptiles Class Reptilia
Includes snakes, lizards, turtles, crocodiles, and alligators Can live totally on land

71 Adaptations for living on land include
Scales to prevent dehydration Lungs for breathing The amniotic egg Figure 17.35

72 Reptiles are ectotherms, which obtain their body heat from the environment

73 Reptiles diversified extensively during the Mesozoic Era
Dinosaurs included the largest animals ever to live on land Figure 17.36

74 Birds Class Aves Evolved during the great reptilian radiation of the Mesozoic era Evolved the ability to fly

75 Bird anatomy and physiology are modified for flight
Bones are honeycombed, which makes them lighter Some specific organs are absent, which reduces weight A warm, constant body temperature is maintained through endothermy

76 A bird’s wings Illustrate the same principles of aerodynamics as the wings of an airplane Airfoil Figure 17.37

77 Mammals Class Mammalia
Evolved from reptiles about 225 million years ago Includes mostly terrestrial organisms

78 Two features are mammalian hallmarks
Hair Mammary glands that produce milk and nourish the young

79 There are three major groups of mammals
Monotremes, the egg-laying mammals, constitute the first group Figure 17.38a

80 Most mammals are born rather than hatched and are nurtured inside the mother by an organ called a placenta

81 The second group of mammals, marsupials, are the so-called pouched mammals
Figure 17.38b

82 Eutherians are also called placental mammals
Their placentas provide more intimate and long-lasting association between the mother and her developing young than do marsupial placentas Figure 17.38c

83 THE HUMAN ANCESTRY Humans are primates

84 The Evolution of Primates
Primate evolution Provides a context for understanding human origins

85 Primates Early primates
Evolved from insect-eating mammals during the late Cretaceous period Early primates Were small, arboreal mammals

86 The distinguishing characteristics of primates were shaped by the demands of living in trees

87 Primate characteristics include
Limber shoulder joints Eyes in front of the face Excellent eye-hand coordination Extensive parental care Figure 17.39

88 Taxonomists divide primates into two main groups
Prosimians Anthropoids

89 Prosimians include Lemurs, lorises, pottos, and tarsiers Figure 17.40a

90 Anthropoids include Monkeys Figure 17.40b, c

91 Apes, the closest relatives to humans
Figure 17.40d–g

92 Humans Figure 17.40h

93 The Emergence of Humankind
Humans and apes have shared a common ancestry for all but the last 5–7 million years

94 Prosimians Anthropoids Monkeys Apes Chim-panzees Humans Gibbons
Gorillas Humans Orangutans New World monkeys Old World monkeys Prosimians (lemurs, lorises, pottos, and tarsiers) Ancestral primate Figure 17.41

95 Some Common Misconceptions
Our ancestors were not chimpanzees or any other modern apes Chimpanzees and humans represent two divergent branches of the anthropoid tree

96 Human evolution Is not a ladder with a series of steps leading directly to Homo sapiens Is more like a multibranched bush than a ladder

97 Homo sapiens neanderthalensis Homo sapiens sapiens
Australopithecus boisei Homo erectus Australopithecus robustus Homo habilis Australopithecus africanus Ardipithecus ramidus Australopithecus afarensis Figure 17.42

98 Upright posture and an enlarged brain appeared at separate times during human evolution

99 Australopithecus and the Antiquity of Bipedalism
Before there was the genus Homo, several hominid species of the genus Australopithecus walked the African savanna

100 Fossil evidence pushes bipedalism in A
Fossil evidence pushes bipedalism in A. afarensis back to at least 4 million years ago Figure 17.43

101 All Australopithecus species were extinct by about 1.4 million years

102 Homo habilis and the Evolution of Inventive Minds
Homo habilis, “handy-man” Had a larger brain Probably made stone tools

103 Homo erectus and the Global Diversity of Humanity
Homo erectus was the first species to extend humanity’s range from Africa to other continents The global dispersal began about 1.8 million years ago

104 Homo erectus Was taller than H. habilis Had a larger brain
Gave rise to Neanderthals

105 The Origin of Homo sapiens
The oldest known post–H. erectus fossils Date back more than 300,000 years Are found in Africa

106 Many paleoanthropologists consider these fossils as the earliest forms of our species, Homo sapiens
The famous fossils of modern humans from the Cro-Magnon caves of France date back about 35,000 years

107 Two hypotheses regarding the origins of modern humans exist
The multiregional hypothesis The “Out of Africa” hypothesis (also called the replacement hypothesis)

108 The multiregional hypothesis
States that modern humans evolved simultaneously in different parts of the world States that Homo erectus spread from Africa into other continents between 1 and 2 million years ago

109 Homo sapiens Interbreeding Homo erectus in Africa
Austral-asian African European Asian Interbreeding 1–2 million years ago Homo erectus in Africa (a) Multiregional hypothesis Figure 17.44a

110 The “Out of Africa” hypothesis
States that modern humans spread out from Africa about 100,000 years ago

111 Homo sapiens Homo erectus in Africa
Austral-asian African European Asian 100,000 years ago Homo sapiens in Africa Homo erectus in Africa (b) “Out of Africa” hypothesis Figure 17.44b

112 Cultural Evolution Culture
Is the transmission of accumulated knowledge over generations

113 Cultural evolution has had three major stages

114 First, nomads who were hunter-gatherers
Made tools Created art Figure 17.45

115 Second, the development of agriculture
Third, the Industrial Revolution

Cultural evolution Made Homo sapiens a new force in the history of life Humans are changing the world faster than many species can adapt The rate of extinction in the twentieth century was 50 times greater than the average for the past 100,000 years

117 This rapid rate of extinction is mainly a result of habitat destruction
The exploding human population now threatens Earth’s ecosystems

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