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Essentials of The Living World First Edition GEORGE B. JOHNSON 15 Evolution of Animals PowerPoint® Lectures prepared by Johnny El-Rady Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 15.1 General Features of Animals All animals are multicellular heterotrophs They all require oxygen for respiration Animals are diverse in form There are ~ 10 million living species Only ~ 54,000 are vertebrates (possessing a backbone) The rest are invertebrates (lacking a backbone) There are about 36 phyla Most occur in the sea Three phyla dominate life on land Arthropoda; Mollusca; Chordata Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Animals lack cell walls They are usually quite flexible Animals are mobile They move more rapidly and in more complex ways than members of other kingdoms Most animals reproduce sexually An animal develops from a zygote by a characteristic process of embryonic development Morula Blastula Gastrula Details vary widely between phyla Provide clues to evolutionary relatedness Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 15.2 Evolutionary trends among the animals Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 15.2 Sponges and Cnidarians: The Simplest Animals The Kingdom Animalia consists of two subkingdoms Parazoa Animals that lack symmetry and possess neither tissues nor organs 1 phylum: Porifera (sponges) Eumetazoa Animals that have symmetry and in most cases tissues and organs About 35 phyla Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Sponges Sponges are the simplest animals Bodies consist of little more than masses of specialized cells embedded in a gel-like matrix The adult sponge is shaped like a vase It is anchored in place on the seafloor Fig. 15.3 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Sponges are perforated by tiny holes Basis of the phylum name Porifera Unique flagellated cells called choanocytes or collar cells, line the body cavity of the sponge Beating of the flagella draws water in through the pores and drives it through the cavity The sponge is a ”filter-feeder” The choanocytes of sponges very closely resemble a kind of protist called choanoflagellates These may be the ancestors of all animals Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Cnidarians The structure of eumetazoans is much more complex than that of sponges Radially symmetric eumetazoans form two distinct embryonic layers An outer ectoderm epidermis An inner endoderm gastrodermis A jelly-like layer called the mesoglea forms between the epidermis and gastrodermis Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Cnidarians There are two radially symmetric phyla Together, they are called Radiata 1. Cnidaria Hydra Fig. 15.4 2. Ctenophora A minor phylum that includes the comb jellies Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Cnidarians A major evolutionary innovation among the radiates is extracellular digestion of food In radiates, digestion begins in the gastrovascular cavity Cnidarians are carnivores that capture their prey with tentacles Bear unique stinging cells called cnidocytes Contain a small but powerful harpoon called a nematocyst Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Cnidarians have two basic body forms Medusae Free-floating, gelatinous and often umbrella-shaped Polyps Cylindrical, pipeshaped and usually attached to a rock Fig. 15.5 Cnidarians may exist exclusively as either/or Others alternate between the two phases Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 15.3 The Advent of Bilateral Symmetry Radiates are radially symmetrical Have a regular arrangement of parts around a central axis All other eumetazoans are bilaterally symmetrical Have right and left halves that are mirror images Fig. 15.6 Dorsal (top) vs. Ventral (bottom) Anterior (front) vs. Posterior (back) Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Bilaterally symmetrical animals have evolved a definite head end, a process called cephalization Solid worms are the simplest of all bilaterally symmetrical animals Nervous system Ectoderm Mesoderm Endoderm Lack internal cavities, except for digestive tract Acoelomate + Fig. 15.7 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Flatworms Members of Platyhelminthes Planaria The largest phylum of solid worms Simplest animals in which organs occur Some species are free-living Most species are parasitic Tapeworms Fig. 15.8a Flukes Many require two or more hosts to complete their life cycle Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Flatworms Have incomplete gut with only one opening Cannot eat, digest and excrete food simultaneously Have an excretory system consisting of a network of tubules running throughout the body Have a simple nervous system Lack a circulatory system Most are hermaphroditic Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 15.4 The Advent of a Body Cavity The evolution of an internal body cavity was important for three reasons Circulation Rapid passage of material Movement Muscle-driven body movement Organ function Little deformation by surrounding muscles Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Three kinds of body plans Fig. 15.9 Acoelomates Have no body cavity Pseudocoelomates Have body cavity between mesoderm and endoderm Pseudocoel Coelomates Have body cavity entirely within mesoderm Coelom Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Pseudocoelomates There are seven phyla The pseudocoel serves as a hydrostatic skeleton Gains rigidity from being filled with fluid under pressure Therefore muscles can work against this “skeleton” Lack a defined circulatory system Two important phyla Cilia aid in feeding and locomotion Nematoda Fig. 15.10 Rotifera Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Phylum Nematoda: The Roundworms Nematodes are bilaterally symmetrical, cylindrical, unsegmented worms Covered by a thick, flexible cuticle Mouth is equipped with piercing organs called stylets Food passes through the mouth by the sucking action of the pharynx Lack flagella or cilia Reproduction is sexual Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Phylum Nematoda: The Roundworms Caenorhabditis elegans Only animal whose complete cellular anatomy is known First animal whose genome was fully sequenced Trichinella sp. Cause trichinosis Acquired from pigs Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Mollusks The bulk of the animal kingdom consists of coelomates A major advantage of the coelomate body plan is that it allows mesoderm–endoderm contact In pseudocoelomates, the body cavity limits developmental interaction between the tissues Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Mollusks Only major phylum of coelomates without a segmented body The second largest animal phylum, after Arthropods The body consists of three distinct parts Head-foot; Visceral mass; Mantle Gills capture O2 from water and release CO2 The radula is a rasping, tongue-like organ Used to scrape algae off rocks Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The three major groups of mollusks Fig. 15.11 Gastropods Snails and slugs Bivalves Clams, oysters and scallops Cephalopods Octopuses and squids Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Annelids Segmentation is the building of a body from a series of similar segments It offers evolutionary flexibility Small change in existing segment can produce a new segment with a different function The first segmented animals to evolve were the annelid worms, phylum Annelida Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Most annelid species are marine About one-third are terrestrial Representative annelids Fig. 15.12 Earthworm Shiny bristle worm Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The basic body plan is a tube within a tube Three characteristics Repeated segments Separate segments able to expand or contract independently Specialized segments Front segments contain the worm’s sensory organs Connections Materials and information pass through partitions in the segments Segmentation underlies the body organization of all complex coelomate animals Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Arthropods Arthropods belong to the phylum Arthropoda The most successful of all animal groups 2/3rd of all named species 80% of all arthropods are insects Scientists estimate that a quintillion insects are Fig. 15.13 alive at any one time Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display All arthropods have jointed appendages They have a rigid external skeleton made up of chitin This exoskeleton protects the animals and provides sites for muscle attachment It is brittle, so its thickness limits arthropod body size Arthropod bodies are segmented Most larval stages have many segments These fuse into functional groups in the adult Fig. 15.14 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Major kinds of arthropods Arachnids (spiders, ticks, mites) Crustaceans (lobsters, crabs, shrimps) Centipedes and millipedes Insects Fig. 15.15 Beetle Flea Honeybee Grasshoppers Moth Dragonfly Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 15.5 Redesigning the Embryo In the coelomates there are two different developmental patterns In protostomes, the mouth develops from or near the blastopore The anus (if present) develops later from another region of the embryo In deuterostomes, the anus develops from or near the blastopore The mouth develops later from another region of the embryo Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 15.16 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 15.16 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Deuterostomes differ from protostomes in three other fundamental embryological features 1. Cleavage pattern In protostomes, the egg cleaves spirally In deuterostomes, the egg cleaves radially 2. Developmental fate of cells In protostomes, the cells are committed even early on In deuterostomes, the commitment occurs later 3. Origination of coelom In protostomes, it forms directly from the mesoderm In deuterostomes, it forms indirectly via the archenteron Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Echinoderms Echinoderms belong to the phylum Echinodermata They have an endoskeleton composed of hard calcium-rich ossicles that are often fused They consist of about 6,000 living marine species Sand dollar Feather star Sea urchin Sea star Fig. 15.17 Sea cucumber Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Echinoderms are bilaterally symmetrical as larvae But they become radially symmetrical as adults This could be an environmental adaptation Adults have a five-part body plan The key evolutionary innovation is the development of a water vascular system A fluid-filled system with a central ring canal and five radial canals Thousands of tiny, hollow tube feet extend from each radial canal Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Chordates Chordates are members of the phylum Chordata They are deuterostomes that employ a truly internal endoskeleton Chordates are quite diverse Lancelets Tunicate Fig. 15.18 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Distinguishing features of chordates 1. Notochord A stiff, but flexible rod, that forms beneath the nerve cord 2. Nerve cord A single dorsal nerve to which other nerves are attached 3. Pharyngeal slits A series of slits behind the mouth into the pharynx 4. Postanal tail A tail that extends beyond the anus All chordates have all four of these at some time in their life Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Vertebrates With the exception of tunicates and lancelets, all chordates are vertebrates Distinguishing features of vertebrates 1. Backbone A bony vertebral column replaces the notochord 2. Head Well-differentiated, with skull and brain Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Vertebrates All vertebrates have an internal skeleton made of bone and cartilage against which the muscles work This makes possible great size and movement Lion Fig. 15.18c Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 15.6 Overview of Vertebrate Evolution The Earth’s past is divided into large blocks of time called eras Subdivided into periods Subdivided into epochs Subdivided into ages Virtually all of the surviving animal groups originated in the sea at the beginning of the Paleozoic Era During or soon after the Cambrian period (545490 mya) Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 15.6 Overview of Vertebrate Evolution The Cambrian period was a period of experimentation with different body forms and ways of life Some led to contemporary animal phyla Trilobites appear to be the ancestors of horseshoe crabs Others failed and became extinct Ammonites Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 15.6 Overview of Vertebrate Evolution The first vertebrates evolved around 470 mya in the oceans Fishes without jaws Invasion of the land First – fungi and plants (around 500 mya) Second – arthropods (around 410 mya) Third – vertebrates (360-280 mya) Amphibians were the first to live on land Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Mass extinctions are particularly sharp declines in species diversity Create vacant niches, allowing rapid evolution Five have occurred The most dramatic is the third Occurred at the end of the Paleozoic era Estimated 96% of all marine species became extinct The most famous and well-studied is the fourth Occurred in the Mesozoic era Dinosaurs became extinct We are living during the fifth Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 15.7 Fishes Dominate the Sea Fishes constitute about half of all vertebrates They are are the most diverse and successful group of vertebrates They provided the evolutionary base for invasion of land by amphibians Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 15.19 Vertebrate family tree Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Characteristics of Fishes Fishes vary in size, shape, color and appearance However, they all share these four characteristics 1. Gills Used to extract dissolved oxygen gas from water 2. Vertebral column An internal skeleton with a spine surrounding the dorsal nerve cord 3. Single-loop blood circulation Blood flow: Heart Gills Body Heart again 4. Nutritional deficiencies Inability to synthesize the aromatic amino acids Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The earliest fishes were jawless and toothless Sucked up small food particles from ocean floor Agnathans survive today as hagfish and parasitic lampreys These fishes were eventually replaced by larger, heavier, jawed fishes that were predators Jaws seem to have evolved from cartilage arch supports The heavier, jawed fish were in turn replaced by faster fishes Sharks and bony fishes Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Sharks The Class Chondrichthyes adopted a light skeleton made up of strong, flexible cartilage Skates and rays are flattened sharks that are bottom-dwellers Have the most advanced fish reproduction system Galápagos shark Fig. 15.20 Shark eggs are fertilized internally About 40% lay fertilized eggs Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Bony Fishes The Class Osteichthyes adopted a heavy internal skeleton made of bone Serves as base for attachment of strong muscles Fig. 15.21 Regulation of buoyant density occurs via a swim bladder By adjusting the amount of gas in it, fish rise up or down Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Bony Fishes The most successful of all vertebrates Of the ~ 30,800 species of living fishes, ~30,000 are bony fishes Lateral line system Detects changes in water pressure Operculum Covers gills Its flexing pumps water over the gills Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 15.8 Amphibians and Reptiles Invade the Land Amphibians are direct descendants of fishes They are the first vertebrate to walk on land They include Frogs Salamanders Caecilians Fig. 15.22 Red-eyed tree frog Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Characteristics of Amphibians 1. Legs Found in frogs and salamanders, but not in Caecilians Fig. 15.23 Evolution of legs Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Characteristics of Amphibians 2. Lungs Provide a more efficient means of respiration than gills 3. Cutaneous respiration Respiration directly across the skin supplements the use of lungs 4. Pulmonary veins Two large veins that return aerated blood to the heart for repumping 5. Partially divided heart Separates the blood circulation into two separate paths Pulmonary and systemic Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display History of Amphibians Amphibians were the dominant land vertebrates for 100 million years At their peak, 40 families existed Only two of these families survived the Age of Dinosaurs About 4,850 species of amphibians exist today Class Amphibia Order Anura (frogs) Order Urodela (salamanders) Order Apoda (caecilians) Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Reptiles Reptiles replaced amphibians as the dominant terrestrial vertebrates There are ~ 7,000 species of living reptiles Among the most important reptile characteristics are: Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 1. Amniotic egg Watertight egg Contains four membranes Chorion: Allows O2 entry Amnion: Fluid-filled cavity Yolk sac: Provides food Allantois: Excretes waste 2. Dry skin Fig. 15.24 Covers body and prevents water loss 3. Thoracic breathing Increases lung capacity Plus, leg arrangement to better support body weight Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 15.9 Birds Master the Air Birds evolved from small bipedal dinosaurs about 150 mya Birds still retain many reptilian characteristics 1. They lay amniotic eggs 2. They have reptilian scales on feet and lower legs So what distinguishes birds from living reptiles? Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 1. Feathers Derived from reptilian scales Lightweight and easily replaced when damaged Fig. 15.25 2. Flight skeleton Bones are thin and hollow Have a keeled breastbone (the wishbone) Have a fused collarbone Birds, like mammals, are endothermic However, they maintain body temperatures much higher than most mammals Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display History of Birds The oldest bird fossil is that of Archaeopteryx Had teeth and solid bones By the early Cretaceous period, a diverse array of birds had evolved Fig. 15.26 About 8,600 species of birds exist today Class Aves Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 15.10 Mammals Adapt to Colder Times Mammals (class Mammalia) evolved about 220 mya They share three characteristics with mammals today 1. Mammary glands Females have mammary glands which produce milk 2. Hair Keratin-made filaments that provide insulation 3. Middle ear Three middle ear bones that amplify vibration Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display History of Mammals They have been around since the time of dinosaurs The first mammals were tiny shrew-like creatures Lived in trees chasing insects Over 4,500 species of mammals exist today Almost one-quarter are bats! There are only 233 known species of primates Humans evolved less than 2 mya There have been at least three species Only Homo sapiens is alive today! Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Other Characteristics of Modern Mammals Endothermy Allows colonization of severe environments Depends on 1. More efficient blood circulation Provided by the four-chambered heart 2. More efficient breathing Provided by the diaphragm Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Other Characteristics of Modern Mammals Placenta Characteristic of most mammals Brings the bloodstream of mother and fetus into close contact The two don’t mix Fig. 15.27 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Other Characteristics of Modern Mammals Teeth Reptiles have homodont dentition Teeth are all the same Mammals have heterodont dentition Teeth are of different types specialized for different feeding types Hooves and horns Keratin is the structural building material in claws, hooves, and horns Hooves are specialized keratin pads on the toes of horses, cows and other running mammals Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Today’s Mammals Monotremes: Egg laying mammals The only living examples Duck-billed platypus Two species of echidna (spiny anteater) Echidna Have reptilians and mammalian features Fig. 15.28a Females lack well-developed nipples Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Today’s Mammals Marsupials: Pouched mammals Fertilized egg is surrounded by chorion and amniotic membranes, but no shell The embryo is nourished by an abundant yolk After embryo is born, it crawls into the marsupial pouch It latches onto a nipple and continues its development Kangaroo Fig. 15.28b Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Today’s Mammals Placental mammals Produce a true placenta Nourishes the embryo throughout its entire development The placenta forms from both fetal and maternal tissue Lion Fig. 15.28c Most species living today are in this group Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display