Animal Evolution – The Invertebrates

Comparing Key Groups  Evolutionary trends toward Greater size Compartmentalization (division of labor among cells, tissues, and organs) Integration of specialized activities that keep the organism alive

Body Symmetry: Radial and Bilateral  Most animals are bilateral

Body Organization  Cephalization Sensory cells concentrated at the head  Segmentation Repetition of body units, front-to-back

Body Cavities  Most bilateral animals have a coelom and a complete gut

Key Concepts: INTRODUCING THE ANIMALS  Animals Multicelled heterotrophs (ingest other organisms) Grow and develop through a series of stages Actively move about during all or part of life cycle  Cells of most animals form tissues and extracellular matrixes

Sponges (Phylum Porifera)  Sponges No symmetry, tissues, or organs Flattened cells line the body wall (many pores; spikes of silica and/or proteins) Filter feeders (flagellated collar cells absorb food; amoeboid cells digest and distribute it) Zygote develops into free-living larva

Sponges

Cnidarians (Phylum Cnidaria)  Jellyfishes, corals, and sea anemones Radial, tentacled carnivores Gastrovascular cavity (respiration and digestion) True epithelial tissues with a jellylike matrix in between Simple nervous system

Cnidarian Body Plans

Unique Cnidarian Weapons  Nematocysts Used to capture prey and for defense

Cnidarian Predators

Cnidarian Life Cycles

Flatworms (Phylum Platyhelminthes)  Free-living turbellarians (planarians), parasitic tapeworms and flukes Simplest animals with organ systems Paired nerve cords

Parasite Life Cycle: Blood Fluke

Parasite Life Cycle: Tapeworm

Annelids  Segmented worms (earthworms, polychaetes) and leeches Closed circulatory system Digestive and excretory systems Nervous system, ganglia in each segment Muscles and fluid in chambers act as a hydrostatic skeleton

secretory organ head end

Polychaete

Mollusks (Phylum Mollusca)  Including gastropods (snails), bivalves (scallops), chitons, nudibranchs, cephalopods 100,000 named species

Aquatic Snail Body Plan

Cephalopods  The fastest (squids), largest (giant squids), and smartest (octopuses) invertebrates  Have a mantle Sheetlike part of the body mass, draped back on itself

Cephalopods

Cuttlefish Body Plan

Roundworms (Phylum Nematoda)  More than 22,000 kinds of roundworms Free-living decomposers or parasites Some agricultural pests and human parasites Cylindrical body with bilateral features A complete gut Organ systems in a false coelom

Parasitic Roundworms

Key Concepts: BILATERAL INVERTEBRATES  Most animals show bilateral symmetry  Bilateral animals have tissues, organs, and organ systems  All adult tissues arise from two or three simple layers that form in early embryos

Simple Arthropods  Trilobite, millipede, centipede

Arthropod Characteristics  Key arthropod adaptations Hardened exoskeleton Jointed appendages Specialized and fused segments (wings) Efficient respiratory and sensory structures (eyes, antennae)

Chelicerates  Horseshoe crabs and arachnids (spiders, scorpions, ticks, and mites) Predators, parasites, or scavengers

Crustaceans  Mostly marine crustaceans (crabs, lobsters, barnacles, krill, and copepods)

Insect Diversity

Unwelcome Arthropods  Spiders, ticks, and mosquitoes

Echinoderms  Sea stars, sea urchins, sea cucumbers, etc. Exoskeleton with spines, spicules, or plates of calcium carbonate Water-vascular system with tube feet Adults are radial, but bilateral traits appear in larval stages

Echinoderms: “Spiny-Skinned”

Fig , p.381

Animal Evolution – The Vertebrates

Chordate Heritage  Four features define chordates A notochord A dorsal hollow nerve cord A pharynx with gill slits A tail extending past the anus  All features form in embryos May or may not persist in adults

Invertebrate Chordates  Tunicates and lancelets (marine filter-feeders)

Lancelet Body Plan

Craniates  Chordates with a braincase of cartilage or bone Hagfish (jawless fish): Simplest modern craniate

Vertebrate Evolution  Key innovations laid the foundation for adaptive radiations of vertebrates Vertebral column of cartilaginous or bony segments Jaws evolved in predatory fishes Gills evolved in water, then lungs for dry land Paired fins were a starting point for other limbs  Gill-Supporting Structures

Key Concepts: TRENDS AMONG VERTEBRATES  In some vertebrate lineages, a backbone replaced the notochord as the partner of muscles used in motion  Jaws evolved, sparking the evolution of novel sensory organs and brain expansions  On land, lungs replaced gills, and more efficient blood circulation enhanced gas exchange  Fleshy fins with skeletal supports evolved into limbs, now typical of vertebrates on land

Jawed Fishes and Tetrapods  Jawed fishes Cartilaginous fishes (sharks and rays) Bony fishes  Body plans adapted to life in water Streamlined shape reduces drag Swim bladder (in bony fishes) adjusts buoyancy

Cartilaginous Fishes

Bony Fishes  The most diverse vertebrates Lungfishes Lobe-finned fishes (coelacanth) Ray-finned fishes

Early Lineages  Coelacanth, lungfish, and Devonian tetrapod

Amphibians  Frogs, toads, and salamanders Carnivorous vertebrates Adapted to life on land (lungs, 3-chambered heart) Nearly all return to the water to reproduce

Amphibian Evolution

Amniotes  First vertebrates able to complete their life cycle on dry land Water-conserving skin and kidneys Amniote eggs (four membranes) Active life-styles

Dinosaur Extinctions  K-T asteroid impact hypothesis A huge asteroid impact caused extinction of last dinosaurs; spared earliest birds and mammals

Modern Reptiles  Major Groups Turtles (shell attached to skeleton) Lizards (the most diverse reptiles) Snakes (limbless) Crocodilians (closest relatives of birds)

Fig , p.397

Reptile Characteristics  General characteristics Live on land or in water Cold-blooded Have a cloaca (opening for wastes and reproduction) Eggs are fertilized in the body, usually laid on land

Fig , p.396 cloaca olfactory lobe (sense of smell) hindbrain, midbrain, forebrain spinal cord vertebral column gonad kidney (control of water, solute levels in internal environment) unmatched rows of teeth on upper and lower jaws snout stomach esophagus lungheartliverintestine

Birds  Birds are the only modern animals with feathers

Bird Eggs  Birds are warm-blooded amniotes

Adaptations for Flight and Migration  Feathers, lightweight bones, and highly efficient respiratory and circulatory systems

Mammals  Animals with hair, females that nourish young with milk from mammary glands, a single lower jawbone and four kinds of teeth

Modern Mammals  Three major lineages Egg-laying mammals (monotremes) Pouched mammals (marsupials) Placental mammals, the most diverse and widespread mammals

Three Major Lineages

Placental Mammals

Primates

Primate Evolution  Key trends Better daytime vision Upright walking (bipedalism) More refined hand movements Smaller teeth Bigger brains Social complexity (extended parental care; culture evolved in some lineages)

The Foramen Magnum  Four-legged walkers versus upright walkers

Emergence of Early Humans  Hominoids and hominids originated in Africa

Australopiths: Upright Walking

Early Humans  Humans (Homo) arose 2 million years ago H. habilis was an early toolmaking species H. erectus dispersed into Europe and Asia

Emergence of Modern Humans  Extinct Neandertals and modern humans are close relatives with distinct gene pools  Modern H. sapiens evolved 195,000 years ago

Dispersal of Homo sapiens  Based on fossils and studies of genetic markers