CHAPTER 17 The Evolution of Animals Figures 17 1 17 3 PowerPoint Lecture Slides for Essential Biology Second Edition Essential Biology with Physiology Neil Campbell Jane Reece and Eric Simon Presentation prepared by Chris C Romero Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings Zoologists estimate that about a billion billion 1018 individual arthropods populate the Earth Tapeworms can reach lengths of 20 meters in the human intestine Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings 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 Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings 1 BIOLOGY AND SOCIETY INVASION OF THE KILLER TOADS The incredible diversity of animals Arose through hundreds of millions of years of evolution Can be quickly threatened Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings The Australian quoll Is a catlike creature that preys on many small animals such as toads Figure 17 1a Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings 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 Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings 2 THE ORIGINS OF ANIMAL DIVERSITY Animal life began in the Precambrian seas with the evolution of multicellular creatures that ate other organisms Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings What Is an Animal Animals Are eukaryotic multicellular heterotrophic organisms that obtain nutrients by ingestion Digest their food within their bodies Figure 17 2 Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings Most animals reproduce sexually and then proceed through a series of developmental stages Haploid Sperm Egg 2 1 Meiosis Fertilization Zygote fertilized egg Adult 3 Diploid Blastula cross section 7 Metamorphosis Digestive tract Outer cell layer Primitive ectoderm gut 6 5 Early gastrula Larva Inner cell layer endoderm Figure 17 3 4 Later gastrula Opening Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings 3 Most animals have muscle cells and nerve cells that control the muscles Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings Early Animals and the Cambrian Explosion Animals probably evolved from a colonial protist that lived in the Precambrian seas Digestive cavity Reproductive cells 1 Early colony of protists aggregate of identical cells 2 Hollow sphere shown in cross section Somatic cells 3 Beginning of cell specialization 4 Infolding 5 Gastrula like protoanimal Figure 17 4 Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings At the beginning of the Cambrian period 545 million years ago animals underwent a rapid diversification Figure 17 5 Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings 4 What ignited the Cambrian explosion Many hypotheses exist Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings Animal Phylogeny To reconstruct the evolutionary history of animal phyla researchers must depend on clues from comparative anatomy and embryology Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings Four key evolutionary branch points have been hypothesized Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings 5 Sponges Cnidarians Flatworms Roundworms Mollusks Annelids Arthropods Echinoderms Coelom from cell masses Chordates Coelom from digestive tube 4 Pseudocoelom True coelom No body cavity 3 Body cavities Radial symmetry Bilateral 2 symmetry True tissues 1 Multicellularity Figure 17 6 Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings The first branch point is defined by the presence of true tissues Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings The second major evolutionary split is based partly on body symmetry a Radial symmetry b Bilateral symmetry Figure 17 7 Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings 6 Third the evolution of body cavities led to more complex animals Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings Body covering Tissue filled region from from ectoderm mesoderm A body cavity Is a fluid filled space separating the digestive tract from the outer body wall a No body cavity e g flatworm Pseudocoelom May be a pseudocoelom or a true coelom Body covering from ectoderm Digestive tract from endoderm b Pseudocoelom e g roundworm Coelom Figure 17 8 Digestive tract from endoderm Muscle layer from mesoderm Body covering from ectoderm Tissue layer lining coelom and suspending Digestive tract from Mesentery internal organs endoderm from c True coelom e g annelid mesoderm Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings Fourth among animals with a true coelom there are two main evolutionary branches which differ in embryonic development Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings 7 MAJOR INVERTEBRATE PHYLA Invertebrates Are animals without backbones Represent 95 of the animal kingdom Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings Sponges Phylum Porifera Includes sessile animals once believed to be plants Lack true tissues Figure 17 9 Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings The body of a sponge Resembles a sac perforated with holes Draws water into a central cavity where food is collected Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings 8 Choanocyte in contact with an amoebocyte Pores Water flow Skeleton fiber Central cavity Choanocyte Amoebocyte Flagella Figure 17 10 Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings Cnidarians Phylum Cnidaria Is characterized by organisms with radial symmetry and tentacles with stinging cells Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings 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 Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings 9 Examples of polyps are Hydras sea anemones and coral animals Figure 17 12 Copyright 2003