27 The Rise of Animal Diversity

Transcription

1 CAMPBELL BIOLOGY IN FOCUS Urry Cain Wasserman Minorsky Jackson Reece 27 The Rise of Animal Diversity Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge

2 Overview: Life Becomes Dangerous Most animals are mobile and use traits such as strength, speed, toxins, or camouflage to detect, capture, and eat other organisms For example, the chameleon captures insect prey with its long, sticky, fast-moving tongue

3 Figure 27.1

4 Concept 27.1: Animals originated more than 700 million years ago Current evidence indicates that animals evolved from single-celled eukaryotes similar to present-day choanoflagellates More than 1.3 million animal species have been named to date; the actual number of species is estimated to be nearly 8 million

5 Fossil and Molecular Evidence Fossil biochemical evidence and molecular clock studies date the common ancestor of all living animals to the period between 700 and 770 million years ago Early members of the animal fossil record include the Ediacaran biota, which dates from about 560 million years ago

6 Figure 27.2 (a) Dickinsonia 2.5 cm costata (taxonomic affiliation unknown) (b) The fossil mollusc Kimberella 1 cm

7 Figure 27.2a (a) Dickinsonia 2.5 cm costata (taxonomic affiliation unknown)

8 Figure 27.2b (b) The fossil mollusc Kimberella 1 cm

9 Early-Diverging Animal Groups Sponges and cnidarians are two early-diverging groups of animals

10 Figure 27.UN01 Sponges Cnidarians Other animal groups

11 Sponges Animals in the phylum Porifera are known informally as sponges Sponges are filter feeders, capturing food particles suspended in the water that passes through their body Water is drawn through pores into a central cavity and out through an opening at the top Sponges lack true tissues, groups of cells that function as a unit

12 Figure 27.3 Flagellum Collar Food particles in mucus Choanocyte Choanocyte Phagocytosis of food particles Amoebocyte Pores Water flow Spicules Amoebocytes Azure vase sponge (Callyspongia plicifera)

13 Figure 27.3a Azure vase sponge (Callyspongia plicifera)

14 Choanocytes, flagellated collar cells, generate a water current through the sponge and ingest suspended food Morphological similarities between choanocytes and choanoflagellates are consistent with the hypothesis that animals evolved from a choanoflagellate-like ancestor Amoebocytes are mobile cells that play roles in digestion and structure

15 Cnidarians Like most animals, members of the phylum Cnidaria have true tissues Cnidarians are one of the oldest groups of animals, dating back to 680 million years ago Cnidarians have diversified into a wide range of both sessile and motile forms, including hydrozoans, jellies, and sea anemones

16 Video: Clownfish Anemone

17 Video: Coral Reef

18 Video: Hydra Budding

19 Video: Hydra Eating

20 Video: Jelly Swimming

21 Video: Thimble Jellies

22 Figure 27.4 (a) Hydrozoa (b) Scyphozoa (c) Anthozoa

23 Figure 27.4a (a) Hydrozoa

24 Figure 27.4b (b) Scyphozoa

25 Figure 27.4c (c) Anthozoa

26 The basic body plan of a cnidarian is a sac with a central digestive compartment, the gastrovascular cavity A single opening functions as mouth and anus Cnidarians are carnivores that use tentacles to capture prey Cnidarians have no brain, but instead have a noncentralized nerve net associated with sensory structures distributed throughout the body

27 Concept 27.2: The diversity of large animals increased dramatically during the Cambrian explosion The Cambrian explosion (535 to 525 million years ago) marks the earliest fossil appearance of many major groups of living animals

28 Evolutionary Change in the Cambrian Explosion Strata formed during the Cambrian explosion contain the oldest fossils of about half of all extant animal phyla

29 Figure 27.5 Sponges Cnidarians Echinoderms Chordates Brachiopods 635 PROTEROZOIC Ediacaran Molluscs Annelids Arthropods PALEOZOIC Cambrian Time (millions of years age)

30 Fossils from the Cambrian period include the first hard, mineralized skeletons Most fossils from this period are of bilaterians, a clade whose members have a complete digestive tract and a bilaterally symmetric form

31 Figure 27.6 Hallucigenia fossil (530 mya) 1 cm

32 Figure 27.6a

33 Figure 27.6b Hallucigenia fossil (530 mya) 1 cm

34 There are several hypotheses regarding the cause of the Cambrian explosion and decline of Ediacaran biota New predator-prey relationships A rise in atmospheric oxygen The evolution of the Hox gene complex

35 Dating the Origin of Bilaterians Molecular clock estimates date the bilaterians to 100 million years earlier than the oldest fossil, which lived 560 million years ago The appearance of larger, well-defended eukaryotes million years ago indicates that bilaterian predators may have originated by that time

36 Figure m (a) Valeria (800 mya): roughly spherical, no structural defenses, soft-bodied 75 m (b) Spiny acritarch (575 mya): about five times larger than Valeria and covered in hard spines

37 Figure 27.7a 15 m (a) Valeria (800 mya): roughly spherical, no structural defenses, soft-bodied

38 Figure 27.7b 75 m (b) Spiny acritarch (575 mya): about five times larger than Valeria and covered in hard spines

39 Concept 27.3: Diverse animal groups radiated in aquatic environments Animals in the early Cambrian oceans were very diverse in morphology, way of life, and taxonomic affiliation

40 Animal Body Plans Zoologists sometimes categorize animals according to a body plan, a set of morphological and developmental traits There are three important aspects of animal body plans Symmetry Tissues Body cavities

41 Symmetry Animals can be categorized according to the symmetry of their bodies or lack of it Some animals have radial symmetry, with no front and back or left and right

42 Figure 27.8 (a) Radial symmetry (b) Bilateral symmetry

43 Two-sided symmetry is called bilateral symmetry Bilaterally symmetrical animals have A dorsal (top) side and a ventral (bottom) side A right and left side Anterior (head) and posterior (tail) ends Many also have sensory equipment concentrated in the anterior end, including a brain in the head

44 Radial animals are often sessile or planktonic (drifting or weakly swimming) Bilateral animals often move actively and have a central nervous system enabling coordinated movement

45 Tissues Animal body plans also vary according to the organization of the animal s tissues Tissues are collections of specialized cells isolated from other tissues by membranous layers During development, three germ layers give rise to the tissues and organs of the animal embryo

46 Figure 27.9 Body cavity Body covering (from ectoderm) Digestive tract (from endoderm) Tissue layer lining body cavity and suspending internal organs (from mesoderm)

47 Ectoderm is the germ layer covering the embryo s surface Endoderm is the innermost germ layer and lines the developing digestive tube, called the archenteron Cnidarians have only these two germ layers Mesoderm is a third germ layer that fills the space between the ectoderm and the endoderm in all bilaterally symmetric animals

48 Body Cavities Most bilaterians possess a body cavity (coelom), a fluid- or air-filled space between the digestive tract and the outer body wall The body cavity may Cushion suspended organs Act as a hydrostatic skeleton Enable internal organs to move independently of the body wall

49 The Diversification of Animals Zoologists recognize about three dozen animal phyla Phylogenies now combine molecular data from multiple sources with morphological data to determine the relationships among animal phyla

50 Video: C. Elegans Crawling

51 Video: Earthworm Locomotion

52 Video: Echinoderm Tubefeet

53 Video: Nudibranchs

54 Video: Rotifer

55 Figure ANCESTRAL PROTIST Metazoa 770 million years ago Eumetazoa 680 million years ago Bilateria 670 million years ago Deuterostomia Lophotrochozoa Ecdysozoa Porifera Ctenophora Cnidaria Hemichordata Echinodermata Chordata Platyhelminthes Rotifera Ectoprocta Brachiopoda Mollusca Annelida Nematoda Arthropoda

56 The following points are reflected in the animal phylogeny 1. All animals share a common ancestor 2. Sponges are basal animals 3. Eumetazoa is a clade of animals (eumetazoans) with true tissues 4. Most animal phyla belong to the clade Bilateria and are called bilaterians 5. Most animals are invertebrates, lacking a backbone; Chordata is the only phylum that includes vertebrates, animals with a backbone

57 Bilaterian Radiation I: Diverse Invertebrates Bilaterians have diversified into three major clades Lophotrochozoa Ecdysozoa Deuterostomia

58 An Overview of Invertebrate Diversity Bilaterian invertebrates account for 95% of known animal species They are morphologically diverse and occupy almost every habitat on Earth This morphological diversity is mirrored by extensive taxonomic diversity The vast majority of invertebrate species belong to the Lophotrochozoa and Ecdysozoa; a few belong to the Deuterostomia

59 Figure Ectoprocta (4,500 species) Lophotrochozoa Mollusca (93,000 species) Nematoda (25,000 species) Ecdysozoa Arthropoda (1,000,000 species) An octopus Annelida (16,500 species) A roundworm Ectoprocts A web-building spider (an arachnid) A fireworm, a marine annelid Hemichordata (85 species) Deuterostomia Echinodermata (7,000 species) An acorn worm Sea urchins and a sea star

60 Figure 27.11a Ectoprocta (4,500 species) Lophotrochozoa Mollusca (93,000 species) An octopus Annelida (16,500 species) Ectoprocts A fireworm, a marine annelid

61 Figure 27.11aa Ectoprocta (4,500 species) Ectoprocts

62 Figure 27.11ab Mollusca (93,000 species) An octopus

63 Figure 27.11ac Annelida (16,500 species) A fireworm, a marine annelid

64 Figure 27.11b Nematoda (25,000 species) Ecdysozoa Arthropoda (1,000,000 species) A roundworm A web-building spider (an arachnid)

65 Figure 27.11ba Nematoda (25,000 species) A roundworm

66 Figure 27.11bb Arthropoda (1,000,000 species) A web-building spider (an arachnid)

67 Figure 27.11c Hemichordata (85 species) Deuterostomia Echinodermata (7,000 species An acorn worm Sea urchins and a sea star

68 Figure 27.11ca Hemichordata (85 species) An acorn worm

69 Figure 27.11cb Echinodermata (7,000 species) Sea urchins and a sea star

70 Arthropod Origins Two out of every three known species of animals are arthropods Members of the phylum Arthropoda are found in nearly all habitats of the biosphere

71 The arthropod body plan consists of a segmented body, hard exoskeleton, and jointed appendages This body plan dates to the Cambrian explosion ( million years ago) Early arthropods show little variation from segment to segment

72 Figure 27.UN02 A fossil trilobite

73 Arthropod evolution is characterized by a decrease in the number of segments and an increase in appendage specialization These changes may have been caused by changes in Hox gene sequence or regulation

74 Figure Experiment Origin of Ubx and abd-a Hox genes? Other ecdysozoans Arthropods Common ancestor Results Onychophorans Red indicates regions in which Ubx or abd-a genes were expressed. Ant antenna J jaws L1 L15 body segments

75 Figure 27.12a Results Red indicates regions in which Ubx or abd-a genes were expressed. Ant antenna J jaws L1 L15 body segments

76 Bilaterian Radiation II: Aquatic Vertebrates The appearance of large predatory animals and the explosive radiation of bilaterian invertebrates radically altered life in the oceans One type of animal gave rise to vertebrates, one of the most successful groups of animals

77 Figure 27.13

78 The animals called vertebrates get their name from vertebrae, the series of bones that make up the backbone Vertebrates are members of phylum Chordata Chordates are bilaterian animals that belong to the clade of animals known as Deuterostomia

79 Early Chordate Evolution All chordates share a set of derived characters Some species have some of these traits only during embryonic development Four key characters of chordates Notochord, a flexible rod providing support Dorsal, hollow nerve cord Pharyngeal slits or pharyngeal clefts, which function in filter feeding, as gills, or as parts of the head Muscular, post-anal tail

80 Video: Clownfish Anemone

81 Video: Coral Reef

82 Video: Manta Ray

83 Video: Sea Horses

84 Figure Notochord Dorsal, hollow nerve cord Muscle segments Mouth Anus Post-anal tail Pharyngeal slits or clefts

85 Lancelets are a basal group of extant, blade-shaped animals that closely resemble the idealized chordate Tunicates are another early diverging chordate group, but they only display key chordate traits during their larval stage The ancestral chordate may have looked similar to a lancelet

86 Figure (a) Lancelet (b) Tunicate

87 Figure 27.15a (a) Lancelet

88 Figure 27.15b (b) Tunicate

89 In addition to the features of all chordates, early vertebrates had a backbone and a well-defined head with sensory organs and a skull Fossils representing the transition to vertebrates formed during the Cambrian explosion

90 The Rise of Vertebrates Early vertebrates were more efficient at capturing food and evading predators than their ancestors The earliest vertebrates were conodonts, softbodied, jawless animals that hunted prey using a set of barbed hooks in their mouth There are only two extant lineages of jawless vertebrates, the hagfishes and lampreys

91 Figure Common ancestor of vertebrates Vertebral column Jaws, mineralized skeleton Lungs or lung derivatives Lobed fins Limbs with digits Myxini (hagfishes) Petromyzontida (lampreys) Chondrichthyes (sharks, rays, chimaeras) Actinopterygii (ray-finned fishes) Actinistia (coelacanths) Dipnoi (lungfishes) Tetrapoda (amphibians, reptiles, mammals) Tetrapods Lobe-fins Osteichthyans Gnathostomes Vertebrates Myxini Petromyzontida Dipnoi Chondrichthyes Actinopterygii Actinistia Tetrapoda

92 Figure 27.16a Common ancestor of vertebrates Vertebral column Jaws, mineralized skeleton Lungs or lung derivatives Lobed fins Limbs with digits Myxini (hagfishes) Petromyzontida (lampreys) Chondrichthyes (sharks, rays, chimaeras) Actinopterygii (ray-finned fishes) Actinistia (coelacanths) Dipnoi (lungfishes) Tetrapoda (amphibians, reptiles, mammals) Tetrapods Lobe-fins Osteichthyans Gnathostomes Vertebrates

93 Figure 27.16b Myxini Actinopterygii Actinistia Petromyzontida Dipnoi Chondrichthyes Tetrapoda

94 Figure 27.16ba Myxini

95 Figure 27.16bb Petromyzontida

96 Figure 27.16bba

97 Figure 27.16bbb

98 Figure 27.16bc Chondrichthyes

99 Figure 27.16bd Actinopterygii

100 Figure 27.16be Actinistia

101 Figure 27.16bf Dipnoi

102 Figure 27.16bg Tetrapoda

103 Today, jawed vertebrates, or gnathostomes, outnumber jawless vertebrates Early gnathostome success is likely due to adaptations for predation including paired fins and tails for efficient swimming and jaws for grasping prey

104 Video: Lobster Mouth Parts

105 Figure m

106 Gnathostomes diverged into three surviving lineages, chondrichthyans, ray-finned fishes, and lobe-fins Humans and other terrestrial animals are included in the lobe-fins

107 Chondrichthyans include sharks, rays, and their relatives The skeletons of chondrichthyans are composed primarily of cartilage This group includes some of the largest and most successful vertebrate predators

108 Ray-finned fishes include nearly all the familiar aquatic osteichthyans The vast majority of vertebrates belong to the clade of gnathostomes called Osteichthyes Nearly all living osteichthyans have a bony endoskeleton

109 Lobe-fins are the other major lineage of osteichthyans A key derived trait in the lobe-fins is the presence of rod-shaped bones surrounded by a thick layer of muscle in their pectoral and pelvic fins Three lineages survive: the coelacanths, lungfishes, and tetrapods, terrestrial vertebrates with limbs and digits

110 Concept 27.4: Several animal groups had features facilitating their colonization of land Some bilaterian animals colonized land following the Cambrian explosion, causing profound changes in terrestrial communities

111 Early Land Animals Members of many animal groups made the transition to terrestrial life Arthropods were among the first animals to colonize the land about 450 million years ago Vertebrates colonized land 365 million years ago

112 The evolutionary changes that accompanied the transition to terrestrial life were much less extensive in animals than in plants

113 Video: Bee Pollinating

114 Video: Butterfly Emerging

115 Figure AQUATIC ANCESTOR TERRESTRIAL ORGANISM CHARACTER GREEN ALGA MARINE CRUSTACEAN AQUATIC LOBE-FIN Anchoring structure Derived (roots) N/A N/A Support structure Derived (lignin/stems) Ancestral Ancestral (skeletal system) Derived (limbs) Internal transport Derived (vascular system) Ancestral Ancestral Muscle/ nerve cells N/A Ancestral Ancestral Protection against desiccation Derived (cuticle) Ancestral Derived (amniotic egg/scales) Gas exchange Derived (stomata) Derived (tracheal system) Ancestral LAND PLANTS INSECTS TERRESTRIAL VERTEBRATES

116 TERRESTRIAL ORGANISM CHARACTER AQUATIC ANCESTOR Figure 27.18a GREEN ALGA Anchoring structure Support structure Internal transport Muscle/nerve cells Protection against desiccation Gas exchange Derived (roots) Derived (lignin/stems) Derived (vascular system) N/A Derived (cuticle) Derived (stomata) LAND PLANTS

117 TERRESTRIAL ORGANISM CHARACTER AQUATIC ANCESTOR Figure 27.18b MARINE CRUSTACEAN Anchoring structure Support structure Internal transport Muscle/nerve cells Protection against desiccation Gas exchange N/A Ancestral Ancestral Ancestral Ancestral Derived (tracheal system) INSECTS

118 TERRESTRIAL ORGANISM CHARACTER AQUATIC ANCESTOR Figure 27.18c AQUATIC LOBE-FIN Anchoring structure Support structure Internal transport Muscle/nerve cells Protection against desiccation Gas exchange N/A Ancestral (skeletal system) Derived (limbs) Ancestral Ancestral Derived (amniotic egg/scales) Ancestral TERRESTRIAL VERTEBRATES

119 Colonization of Land by Arthropods Terrestrial lineages have arisen in several different arthropod groups, including millipedes, spiders, crabs, and insects

120 General Characteristics of Arthropods The appendages of some living arthropods are modified for functions such as walking, feeding, sensory reception, reproduction, and defense

121 Figure Cephalothorax Abdomen Antennae (sensory reception) Head Thorax Swimming appendages (one pair per abdominal segment) Pincer (defense) Mouthparts (feeding) Walking legs

122 The body of an arthropod is completely covered by the cuticle, an exoskeleton made of layers of protein and the polysaccharide chitin The exoskeleton provides structural support and protection from physical harm and desiccation A variety of organs specialized for gas exchange have evolved in arthropods

123 Insects The insects and their relatives include more species than all other forms of life combined They live in almost every terrestrial habitat and in fresh water

124 Figure Lepidopterans Hymenopterans Hemipterans

125 Figure 27.20a Lepidopterans

126 Figure 27.20aa

127 Figure 27.20ab

128 Figure 27.20b Hymenopterans

129 Figure 27.20c Hemipterans

130 Insects diversified several times following the evolution of flight, adaptation to feeding on gymnosperms, and the expansion of angiosperms Insect and plant diversity declined during the Cretaceous extinction, but has been increasing in the 65 million years since

131 Flight is one key to the great success of insects An animal that can fly can escape predators, find food, and disperse to new habitats much faster than organisms that can only crawl

132 Figure 27.21

133 Terrestrial Vertebrates One of the most significant events in vertebrate history was when the fins of some lobe-fins evolved into the limbs and feet of tetrapods

134 The Origin of Tetrapods Tiktaalik, nicknamed a fishapod, shows both fish and tetrapod characteristics It had Fins, gills, lungs, and scales Ribs to breathe air and support its body A neck and shoulders Fins with the bone pattern of a tetrapod limb

135 Figure Fish Characters Scales Fins Gills and lungs Tetrapod Characters Neck Ribs Fin skeleton Flat skull Eyes on top of skull Head Neck Shoulder bones Ribs Scales Eyes on top of skull Flat skull Fin Elbow Radius Humerus Ulna Wrist Fin skeleton

136 Figure 27.22a Eyes on top of skull Flat skull Head Neck Shoulder bones Fin

137 Figure 27.22b Ribs

138 Figure 27.22c Scales

139 Figure 27.22d Elbow Radius Humerus Ulna Wrist Fin skeleton

140 Tiktaalik could most likely prop itself on its fins, but not walk Fins became progressively more limb-like over evolutionary time, leading to the first appearance of tetrapods 365 million years ago

141 Figure Lungfishes Eusthenopteron Panderichthys Tiktaalik Acanthostega Limbs with digits Tulerpeton Silurian Devonian Amphibians Amniotes PALEOZOIC Carboniferous Permian Time (millions of years ago) Key to limb bones Ulna Radius Humerus

142 Figure 27.23a Lungfishes Eusthenopteron Panderichthys Tiktaalik Key to Lobe-fins with limbs with digits limb bones Ulna Silurian PALEOZOIC Radius Devonian Carboniferous Permian Humerus Time (millions of years ago)

143 Figure 27.23b Acanthostega Limbs with digits Tulerpeton Silurian Devonian Amphibians Amniotes PALEOZOIC Carboniferous Permian Time (millions of years ago) Key to limb bones Ulna Radius Humerus

144 Amphibians Amphibians are represented by about 6,150 species including salamanders, frogs, and caecilians Amphibians are restricted to moist areas within their terrestrial habitats

145 Video: Marine Iguana

146 Video: Flapping Geese

147 Video: Snake Wrestling

148 Video: Soaring Hawk

149 Video: Swans Taking Flight

150 Video: Tortoise

151 Figure Salamanders retain their tails as adults. Caecilians have no legs and are mainly burrowing animals. Frogs and toads lack tails as adults.

152 Figure 27.24a Salamanders retain their tails as adults.

153 Figure 27.24b Frogs and toads lack tails as adults.

154 Figure 27.24c Caecilians have no legs and are mainly burrowing animals.

155 Terrestrial Adaptations in Amniotes Amniotes are a group of tetrapods whose living members are the reptiles, including birds, and mammals Amniotes are named for the major derived character of the clade, the amniotic egg, which contains membranes that protect the embryo The extraembryonic membranes are the amnion, chorion, yolk sac, and allantois The amniotic eggs of most reptiles and some mammals have a shell

156 Video: Bat Licking

157 Video: Bat Pollinating

158 Video: Chimp Agonistic

159 Video: Chimp Cracking Nut

160 Video: Gibbon Brachiating

161 Video: Sea Lion

162 Video: Shark Eating Seal

163 Video: Wolves Agonistic

164 Figure Extraembryonic membranes Amnion Allantois Chorion Yolk sac Embryo Amniotic cavity with amniotic fluid Yolk (nutrients) Shell Albumen

165 The Origin and Radiation of Amniotes Living amphibians and amniotes split from a common ancestor about 350 million years ago Early amniotes were more tolerant of dry conditions than early tetrapods The earliest amniotes were small predators with sharp teeth and long jaws

166 Reptiles are one of two living lineages of amniotes Members of the reptile clade includes the tuataras, lizards, snakes, turtles, crocodilians, birds, and some extinct groups

167 Figure Plesiosaurs Crocodilians Pterosaurs Common ancestor of reptiles Common ancestor of dinosaurs Ornithischian dinosaurs Saurischian dinosaurs other than birds Birds Turtles Turtles Tuataras Squamates Squamates Crocodilians Birds Tuataras

168 Figure 27.26a Plesiosaurs Crocodilians Pterosaurs Common ancestor of reptiles Common ancestor of dinosaurs Ornithischian dinosaurs Saurischian dinosaurs other than birds Birds Turtles Tuataras Squamates

169 Figure 27.26b Crocodilians Tuataras Squamates Birds Turtles

170 Figure 27.26ba Crocodilians

171 Figure 27.26bb Birds

172 Figure 27.26bba

173 Figure 27.26bbb

174 Figure 27.26bc Turtles

175 Figure 27.26bd Tuataras

176 Figure 27.26be Squamates

177 Reptiles have scales that create a waterproof barrier Most reptiles lay shelled eggs on land Most reptiles are ectothermic, absorbing external heat as the main source of body heat Birds are endothermic, capable of keeping the body warm through metabolism

178 Mammals are the other extant lineage of amniotes There are many distinctive traits of mammals including Mammary glands that produce milk Hair A fat layer under the skin A high metabolic rate, due to endothermy Differentiated teeth

179 The first true mammals evolved from synapsids and arose about 180 million years ago By 140 million years ago, the three living lineages of mammals had emerged Monotremes, egg-laying mammals Marsupials, mammals with a pouch Eutherians, placental mammals

180 Figure Monotremes Marsupials Eutherians

181 Figure 27.27a Monotremes

182 Figure 27.27aa

183 Figure 27.27ab

184 Figure 27.27b Marsupials

185 Figure 27.27c Eutherians

186 Human Evolution Humans (Homo sapiens) are primates, nested within a group informally called apes

187 Figure New World monkeys Old World monkeys Gibbons Apes Orangutans Gorillas Chimpanzees and bonobos Humans

188 A number of characters distinguish humans from other apes Upright posture and bipedal locomotion Larger brains capable of language, symbolic thought, artistic expression, and the use of complex tools

189 The evolution of bipedalism preceded the evolution of increased brain size in early human ancestors Brain size, body size, and tool use increased over time in Homo species Modern humans, H. sapiens, originated in Africa about 200,000 years ago and colonized the rest of the world from there

190 Figure 27.29

191 Concept 27.5: Animals have transformed ecosystems and altered the course of evolution The rise of animals from a microbe-only world affected all aspects of ecological communities, in the sea and on land

192 Ecological Effects of Animals The oceans of early Earth likely had very different properties than the oceans of today

193 Figure Murky, poorly-mixed Low oxygen Cyanobacteria (a) Ocean conditions before 600 mya Clear, well-mixed High oxygen Eukaryotic algae (b) Changes to ocean conditions by 530 mya

194 Marine Ecosystems The rise of filter-feeding animals likely caused the decline of cyanobacteria and other suspended particles in the oceans during the early Cambrian This resulted in a shift to algae as the dominant producers and changed the feeding relationships in marine ecosystems

195 Terrestrial Ecosystems Terrestrial ecosystems were transformed with the move of animals to land Herbivores, such as the lesser snow goose, can improve the growth of plants at low population sizes through additions of nutrient-rich wastes At high population sizes herbivores can defoliate large tracts of land

196 Figure 27.31

197 Evolutionary Effects of Animals The origin of mobile, heterotrophic animals with a complete digestive tract drove some species to extinction and initiated ongoing arms races between bilaterian predators and prey

198 Evolutionary Radiations Two species that interact can exert strong, reciprocal selective pressures on one another For example, flower form can be influenced by the structure of its pollinators mouth parts, and vice versa

199 Figure 27.32

200 Reciprocal selection pressures can also occur when the origin of new species in one group stimulates further radiation in another group For example, the origin of a new group of animals provides new food sources for parasites, resulting in radiations in parasite groups

201 Human Impacts on Evolution Humans have made large changes to the environment that have altered the selective pressures faced by many species For example, human targeting of large fish for harvesting has led to the reduction in age and size at which individuals reach sexual maturity

202 Figure Age at maturity (years) Year

203 Figure 27.33a

204 Rapid species declines over the past 400 years indicate that human activities may be driving a sixth mass extinction Molluscs, including pearl mussels, have suffered the greatest impact of human-caused extinctions

205 Figure Other invertebrates Molluscs An endangered Pacific island land snail, Partula suturalis Insects Fishes Birds Amphibians Mammals Reptiles (excluding birds) Recorded extinctions of animal species Workers on a mound of pearl mussels killed to make buttons (ca. 1919)

206 Figure 27.34a Other invertebrates Molluscs Insects Fishes Birds Mammals Amphibians Reptiles (excluding birds) Recorded extinctions of animal species

207 Figure 27.34b An endangered Pacific island land snail, Partula suturalis

208 Figure 27.43c Workers on a mound of pearl mussels killed to make buttons (ca. 1919)

209 The major threats imposed on species by human activities include habitat loss, pollution, and competition or predation by introduced, non-native species

210 Figure 27.UN03 Average number of periwinkles killed Southern Northern Source population of crab Southern periwinkles Northern periwinkles

211 Figure 27.UN mya: Cambrian explosion 560 mya: Ediacaran animals Era Neoproterozoic 365 mya: Early land animals Paleozoic Origin and diversification of dinosaurs Mesozoic Diversification of mammals Cenozoic 1, Millions of years age (mya)

212 Figure 27.UN05