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Essentials of Biology Sylvia S. Mader Chapter 19 Lecture Outline Prepared by: Dr. Stephen Ebbs Southern Illinois University Carbondale Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 19.1 Evolution of Animals • Animals are chemoheterotrophic, sexuallyreproducing eukaryotes. • Animals have two tissues that differ from other multicellular eukaryotes. – Muscle tissue – Nervous tissue • The specialized tissues and organs of animals arise from complex changes that occur during development. The Evolutionary Tree of Animals • Our understanding of animal evolution is based upon the limited fossil record. • There are also seven evolutionary trends that appeared during animal evolution. – – – – – – – Multicellularity True tissues and germ layers in the embryo Bilateral symmetry Body cavities Coelomates Segmentation Jointed appendages 19.2 Introducing the Invertebrates • There are several groups of organisms that comprise the invertebrates. – Sponges – Cnidarians such as Hydra – Flatworms – Nematodes and roundworms Sponges: Multicellularity • Sponges are aquatic, multicellular, radiallysymmetric, filter-feeding organisms. • The interior of the sponge is lined with collar cells that engulf food particles. • Sponges can reproduce asexually or sexually. Sponges: Multicellularity (cont.) Cnidarians: True Tissues • Cnidarians are radially-symmetric invertebrates with a ring of stinging cells (cnidocytes). • Cnidarians have two developmental germ layers during development. – Ectoderm – Endoderm • Cnidarians also have two basic body forms. – The tubular, sedentary polyp – The jellylike medusa Cnidarians: True Tissues (cont.) Flatworms: Bilateral Symmetry • Flatworms show bilateral symmetry and have several body systems. – Ladderlike nervous system with cephalization. – A digestive system with a muscular pharynx and a gastrovascular cavity – An excretory system provided by flame cells – Hermaphroditic reproduction • Flatworm can be free-living or parasitic. Flatworms: Bilateral Symmetry (cont.) Roundworms: Pseudocoelomates • Roundworms evolved a complete tube-within-atube digestive tract and a pseudocoelom. • Roundworms lack a skeletal system but use the fluid-filled coelom for support and movement. • Roundworms are nonsegmented with a smooth outside body wall. • Roundworms can be free-living or parasitic. Roundworms: Pseudocoelomates (cont.) 19.3 Protostomes and Deuterostomes Compared • The difference between these two groups involves the developmental fate of the first embryonic opening. – In protostomes, this opening becomes the mouth. – In deuterostomes, this opening becomes the anus. • There are three groups of organisms that are protostomes. – Molluscs – Annelids – Arthropods 19.3 Protostomes and Deuterostomes Compared (cont.) 19.3 Protostomes and Deuterostomes Compared (cont.) Molluscs • The body of a mollusc has three regions. – The visceral mass – The muscular foot – The mantle, which may secrete a shell • There are three main groups of molluscs. – Gastropods – Cephalopods – Bivalves Molluscs (cont.) Molluscs (cont.) • Gastropods, which means stomachfooted, include the snails and conchs. • Gastropods can be either herbivores or carnivores. Molluscs (cont.) Molluscs (cont.) • Cephalopods, meaning head-footed, include the octopi, squid, and nautiluses. • Cephalopods uses tentacles to seize prey and a beak and radula to tear apart food. • Cephalopods have a large brain, extensive nervous system, and highly developed eyes. Molluscs (cont.) Molluscs (cont.) • The bivalves are the clams, scallops, and mussels. • Bivalves have a muscular foot that can be projected from the shell for movement. • Bivalves are generally filter feeders, using an incurrent siphon to bring in food. Molluscs (cont.) Annelids: Segmented Worms • Annelids have segments divided by septa. • The digestive system of annelids has several specialized organs. • Annelids have a closed circulatory system with several hearts and blood vessels. • Tubules called nephridia collect wastes and excrete them from the worm’s body. Annelids: Segmented Worms (cont.) Annelids: Segmented Worms (cont.) Arthropods: Jointed Appendages • The success of arthropods can be linked to five key characteristics. – An exoskeleton that can be shed – Segmentation and jointed appendages – A well-developed nervous system – A variety of respiratory organs – Metamorphosis Arthropods: Jointed Appendages (cont.) Arthropods: Jointed Appendages (cont.) Arthropods: Jointed Appendages (cont.) • Crustaceans are arthropods such as shrimp, crabs, crayfish and lobsters. • All crustaceans share several features. – A head with five appendages – Legs attached to the thorax – A fused head and thorax (cephalothorax) – Abdominal segments with swimmerets. Arthropods: Jointed Appendages (cont.) • There are a wide variety of other arthropods, each with their own unique structures. – Arachnids such as spiders, scorpions, ticks, mites, and horseshoe crabs – Millipedes and centipedes – Insects 19.5 Echinoderms and Chordates • There are two groups of organisms that are deuterostomes. – Echinoderms – Chordates Echinoderms • Echinoderms such as sea stars, sea cucumbers, and sea urchins often show radial symmetry. • The nervous system is a network of nerves in a ring around the mouth and stretching outward radially. • Locomotion is provided by a water vascular system and tube feet. • The water vascular system is also the respiratory, circulatory, and excretory systems. Echinoderms (cont.) Chordates • Chordates display four traits at some point in their life cycle. – A dorsal supporting rod called a notochord – A dorsal tubular nerve cord such as the spinal cord – Pharyngeal pouches – A tail The Invertebrate Chordates • In the invertebrate chordates, the notochord persists rather than being replaced with a vertebral column. • There are two examples of invertebrate chordates, both of which retain the four chordate characteristics as adults. – The tunicates, or sea squirts – The lancelets Evolutionary Trends Among the Chordates • As the invertebrate chordates evolved, major changes can be from one group of chordates to the next. – Evolution of vertebrae – Evolution of the jaw – Evolution of lungs for land colonization – Jointed appendages for movement – Amniotic eggs with adaptations for development on land – Hair and mammary glands Fishes: First Jaws and Lungs • There are three classes of fish. – Jawless fish – Cartilaginous fish – Bony fish • The last remaining jawless fishes are the hagfishes and lampreys. Fishes: First Jaws and Lungs (cont.) • The cartilaginous fishes, such as the sharks, rays, and skates, have skeletons comprised of cartilage. • Sharks have three highly developed senses that help them hunt for prey. – The ability to sense electrical currents in water – The lateral line cells along the body, which sense differences in pressure – A keen sense of smell Fishes: First Jaws and Lungs (cont.) • Most bony fishes are ray-finned fishes, using fins for balance and movement. • The ray-finned fishes use a swim bladder to adjust their buoyancy in the water. • The bony fishes also have scales that protect the body. • The circulatory system of bony fishes is a single circuit. Fishes: First Jaws and Lungs (cont.) • The lobe-finned fishes are bony fishes that have fleshy appendages and lungs. • The lobe-finned fishes were the ancestors of the amphibians. Amphibians: Jointed Vertebrate Limbs • The amphibians evolved a number of features that were different from the lobefinned fishes. – Eyelids – Ears – A larynx, or voice box – Larger brains – A three-chambered heart Amphibians: Jointed Vertebrate Limbs (cont.) Amphibians: Jointed Vertebrate Limbs (cont.) Amphibians: Jointed Vertebrate Limbs (cont.) • Modern amphibians include the frogs, toads, newts, and salamanders. • The term amphibian describes their lifestyle as both aquatic and terrestrial. – Larval stages live in the water. – The adult lives on land but may return to water to reproduce. Amphibians: Jointed Vertebrate Limbs (cont.) Reptiles: Amniotic Egg • Modern reptiles include the turtles, crocodiles, snakes, and lizards. • Reptiles are covered with scales for protection from dehydration and predators. • The tongues of reptiles also evolved to become a sense organ. • Reptiles also have a four chambered heart and well developed lungs. Reptiles: Amniotic Egg (cont.) • Reptile reproduction also evolved to be completely terrestrial and free from water. • Fertilization of the eggs occurs inside the female body. • The amniotic egg and its extraembryonic membranes provide nutrients, protect the embryo, and facilitate waste and gas exchange. Reptiles: Amniotic Egg (cont.) Birds: Feathers • The most unique character of birds is the presence of feathers, which evolved from scales. • The anatomy of birds is designed for flight. – The forelimbs of birds are wings. – The bones of birds are hollow and light due to the presence of air cavities. Birds: Feathers (cont.) • Birds have a four chambered heart like mammals and are endothermic. • Birds have highly developed nervous systems and eyes. • Birds are subdivided into groups based on specific characters. – – – – Type of beak Type of foot Habitat Behavior Mammals: Hair and Mammary Glands • Mammals appeared during the time of the dinosaurs, but did not flourish until after dinosaurs became extinct. • Mammals share two common characters. – Hair – Milk-producing mammary glands • Animals are also endothermic. Mammals: Hair and Mammary Glands (cont.) • Monotremes such as the platypus were the earliest mammals. • Like birds, monotremes have a cloaca, a chamber at the end of the digestive tract for feces, excretory wastes, and sex cells. • Monotremes are egg-laying mammals. Mammals: Hair and Mammary Glands (cont.) • Marsupials have a pouch in which their immature young develop. • All other mammals are placental mammals. • The placenta is a highly modified extraembryonic membrane that facilitates exchange of gases, nutrients, and wastes. 19.6 Human Evolution • The primates evolved from a common ancestor. • There are two suborders of primates. – The prosimians include lemurs and lorises. – The anthropoids include monkeys, apes, and humans. • There are two prominent aspects of primate evolution. – The opposable thumb – Larger and more complex brains Evolution of Hominids • There have been several bipedal hominids that may have been human ancestors. – The primitive australopithecines – Homo habilis, the first hominid to use tools and possibly to speak – Homo erectus, the first hominid to use fire and advanced tools. Evolution of Modern Humans • The ancestral hominid from which modern humans evolved is not clear, but at least two hypotheses have been offered. – The multiregional hypothesis proposes that humans evolved separately from H. erectus in different regions and then later interbred. – The out-of-Africa hypothesis proposes that humans evolved from the H. erectus in Africa, and then migrated across the globe. Evolution of Modern Humans (cont.) Evolution of Modern Humans (cont.) Neanderthals • Neanderthals were a group of European hominids that may have been present when modern humans were evolving. • Neanderthals showed a complex culture and tool-making ability. • Neanderthals eventually either became extinct or may have interbred with humans. Cro-Magnons • Cro-magnons are the closest evolutionary ancestor to humans. • Cro-magnons also demonstrated a complex culture and may have used a spoken language. • Cro-magnons not only made tools, but crafted artwork as well. Cro-Magnons (cont.)