Lecture Outline
Interpreting and Misinterpreting the Past
A. The absence of transitional forms was an early obstacle to Darwin’s theory of evolution.
1. The discovery of Archaeopteryx specimens which display both reptilian and bird
features was significant.
2. Archaeopteryx lived about 150 million years ago.
B. Such fossils are witness to the history of life.
22.1 Overview of the Animal Kingdom
A. Animals are defined by these characteristics:
1. Animals are multicellular (diploid) with tissues arranged into organs and organ
systems.
2. Animals are aerobic and heterotrophic.
3. Animals reproduce sexually, and in some cases asexually, or both.
4. Most animals are motile during at least part of their life cycle.
5. Animal life cycles include a period of embryonic development; germ tissue layers
(ectoderm, endoderm, and in most species, mesoderm) give rise to adult organs.
Vertebrates
Invertebrates
B. Clues in Body Plans
1. Body Symmetry and Cephalization
a. Animals show either radial (round) or bilateral (right and left sides) symmetry.
b. Cephalization means having a definite head end, usually with feeding and
sensory features.
2.Type of Gut
a. Incomplete digestive tracts: The place where food is digested is the gut; some are
saclike with one opening (gastrovacular cavity)—a mouth.
blastopore
b. “Complete” digestive tracts have two openings (mouth and anus) for continuous
food processing, often through specialized regions.
1. Protosomes: flatworms, mollusks, annelids, roundworms, and arthropods
2. deuterostmes: Echinoderms and Chordates
3. Tissue layers
a. Endoderm: inner most, digestive system
b. Ectoderm: outer most layer, skin, nerves
c. Mesoderm: muscles, most internal organs
-develops into the Coelom: bilateral organisms with peritoneum
***more complex then Cnidarians
5. Body Cavities
a. A coelom (lined with peritoneum) is a space between the gut and body wall that
allows internal organs to expand and operate freely.
b. Some animals (flatworms) do not have a coelom (acoelomate) but instead are
packed solidly with tissue between the gut and body wall.
c. Others, such as roundworms, have a “false” coelom (pseudocoelomate), not lined
with peritoneum.
6.Segmentation
a. A segmented animal is composed of repeating body units (for example, the
earthworm).
b. The segments may be grouped and modified for specialized tasks, as for example
in insects.
C. Animal Origins
1. Animals probably arose from Ediacaran ancestors about 610 million years ago.
2. Early animals were thin, flat-bodied, with a good surface-to-volume ratio for
absorbing nutrients.
Invertebrates
Sponges
Cnidarians -Coelenterates
Flatworms - Platyhelminthes
Roundworms - Nematods
Arthropods—The Most Successful Animals
Annelids–Segments Galore
Mollusks
Echinoderms
Vertebrates
Chordates
Poriferans
16.2 Getting Along Well Without Organs
A. Sponges have an asymmetric body with no true tissues, no organs.
1. Between two layers of body cells there is a semifluid matrix with needlelike spicules
for support.
2. Collar cells line the interior chambers.
a. By means of their beating flagella, these cells move large volumes of water in
through body pores and out through the large opening at the top of the body.
b. They also trap suspended food particles in their collars and transfer the food to
amoeba-like cells in the matrix.
3. Most sponges reproduce sexually.
a. Sperm are released into the surrounding water to be picked up by a nearby
sponge and directed to the egg within the matrix.
b. The zygote develops into a free-swimming larva.
B. Cnidarians are radial, tentacled animals that have stinging cells called nematocysts.
1. Cnidarians include jellyfishes, sea anemones, corals, and hydras.
2. Unique stinging devices called nematocysts discharge threads to capture prey and
fend off predators. They are called stinging –celled animals.
3. There are two common body plans:
a. The medusa resembles an umbrella and floats like a tentacle-fringed bell in the
water; oral arms surround the central mouth.
b. The polyp is tubelike and is usually attached to some substrate; it may be solitary
or part of a colony.
4. The digestive cavity is saclike (only a mouth) and can accommodate prey larger than
the cnidarian itself.
5. An outer epidermis covers the body, and an inner gastrodermis lines the digestive
cavity.
a. A nerve net running through both layers coordinates the animal’s response to
stimuli.
b. Some jellyfishes also have sensory cells and contractile cells.
6. A jellylike mesoglea lies between the outer and inner body layers.
a. Jellyfishes have abundant mesoglea helpful in providing buoyancy and in
swimming.
b. Polyps have little mesoglea but use the water in their guts as a hydrostatic
skeleton.
7. The life cycle of a cnidarian may have a polyp and medusa stage, or it may have just
the polyp.
a. The medusa is usually the sexual form with gonads.
b. The zygote develops into a swimming larva called a planula.
16.3 A Gallery of Worms With Simple Organs
A. Flatworms - Platyhelminthes
1. Flatworms are the simplest animals to display organs—a grouping of tissues arranged
in such a manner as to perform specialized functions.
a. The gut is saclike with a single (mouth) opening through which a pharynx
extends for food gathering.
b. Most flatworms are hermaphrodites (both sexes in one body).
2. Turbellarians are free-living predators, but flukes and tapeworms are parasites.
B. Roundworms - Nematods
1. They are bilateral and possess a slender tapered body.
a. The digestive tract is complete–mouth and anus for continuous food processing.
b. Reproductive organs lie in a false coelom filled with fluid.
c. A tough cuticle covers and protects the body.
2. Most roundworms are small and free-living, but some are parasitic on plants and
animals.
a. In trichinosis, undercooked pork is the source of a roundworm that moves from
the digestive tract of the host to encyst in the muscles.
b. Elephantiasis is a severe welling of the legs due to blockage of lymph flow by
small roundworms deposited by a mosquito during feeding.
16.4 Arthropods—The Most Successful Animals
A. Keys to Success
1. Hardened exoskeleton:
a. The arthropod covering is a combination of protein and chitin (plus calcium in
some) that is flexible, lightweight, yet protective.
b. It is a barrier to water loss and can support a body deprived of water’s buoyancy.
c. Exoskeletons restrict growth and so must be shed periodically (molting process).
2. Jointed appendages:
a. Arthropod appendages are jointed.
b. Appendages became specialized for feeding, sensing, locomotion, sperm transfer,
and spinning silk.
3. Fused and specialized segments:
a. Body segments became more specialized, reduced in number, and grouped
together.
b. In some lineages this has resulted in a head, thorax, and abdomen regions.
4. Respiratory structures:
a. Special tubes called tracheas supply oxygen directly to body tissues.
b. This allows high metabolic rates and sustained activity, as in flight.
5. Specialized sensory structures:
a. The compound eye provides a wide angle of vision.
b. Many individual units of the eye allow motion perception.
6. Division of labor:
a. Larval stages concentrate on feeding and growth.
b. Adults specialize in dispersal and reproduction.
c. The process of change from larva to adult is called metamorphosis.
B. Spiders and Their Relatives
1. Chelicerates include some marine species such as horseshoe crabs and the more
familiar arachnids.
2. Arachnids include spiders, scorpions, ticks, and mites.
a. Spiders are keen predators that trap insects in their webs produced as silk strands
from the abdomen; some are poisonous such as the brown recluse and black
widow.
b. Some mites are free-living, others are serious pests of plants and animals; ticks are
notorious blood-suckers and disease-carriers (Lyme disease).
C. Crustaceans
1. Crustaceans—shrimps, lobsters, crabs, barnacles, and pillbugs—get their name from
the "crusty" exoskeleton.
a. These are important components of food webs and serve as human food also.
b. Like other arthropods, they repeatedly molt and shed the exoskeleton.
2. The crustacean body is divided into many segments each of which bears paired
specialized appendages including antennae, mandibles, maxillae, grasping claws, and
legs.
D. A Look at Insect Diversity
1. The body is divided into three regions: head (sensory and feeding), thorax
(locomotion by six legs, two pairs of wings), and abdomen.
2. The complete digestive tract is divided into three regions: foregut, midgut (digestion
and absorption), and hindgut (water reabsorption).
3. Unique small tubes attached to the gut and lying free in the abdominal cavity process
metabolic waste (uric acid) and aid in water retention.
4. Insects display enormous diversity.
a. Their ability to disperse by flight allows the utilization of widely ranging food
sources.
b. Their great success is due to their ability to exploit nature’s resources during
different stages of metamorphosis, such as larvae, nymphs, and pupae.
16.5 Annelids–Segments Galore
A. This phylum includes earthworms, polychaetes, and leeches.
1. The body is bilateral with definite segmentation evidenced on the surface as "rings."
a. A segmented body has great evolutionary potential, for individual parts can
undergo modification and become highly adapted for specialized tasks.
b. Leeches have suckers at both ends; polychaetes have fleshy, paddle-like
parapods.
2. Setae (bristles) which may be many or few in number, project directly from the body.
B. Earthworms are typical annelids
1. Their habit of ingesting dirt particles while scavenging for organic matter makes them
valuable tillers of the soil.
2. The outer body surface is covered with a cuticle; internal partitions define individual
coelomic chambers filled with fluid to provide a hydrostatic skeleton against which
the muscles act during movement.
3. The circulatory system is closed (blood confined to hearts and vessels).
4. Paired nerve cords extend from the brain to run the length of the body with a
ganglion in each segment.
16.6 The Evolutionarily Pliable Mollusks
A. Mollusks have a fleshy, soft bilateral body with a small coelom.
1. Some have a head with eyes and tentacles, some have a shell.
2. All have a mantle, a skirtlike tissue covering the body.
B. Hiding Out, Or Not
1. The chiton is protected by the eight plates surround the soft, edible body.
2. A bivalve not only has its two protected shells but can also burrow in the sand to
disappear from sight of predators; water and suspended food are drawn in, and waste
voided, through openings called siphons, by the action of the cilia on the gills.
3. Nudibranchs (no shells) protect themselves by secreting toxic substances and
incorporating nematocysts from the cnidarians they eat.
C. On the Cephalopod Need for Speed
1. The body of a squid is modified for a highly active predatory life-style; it has tentacles
and beaklike jaws.
2. They move by a type of jet propulsion caused by mantle contractions.
3. To support greater activity, the circulatory system is a closed one; the nervous system
is well developed with a large brain; the eyes form images; and learning and memory
are possible.
16.7 The Puzzling Echinoderms
A. The name of this phylum, Echinodermata, refers to the “spiny skin” made of calcium
carbonate.
1. Members include sea stars, sea urchins, brittle stars, and sea cucumbers.
2. Adults are radially symmetrical; larvae are bilateral.
B. Internally, echinoderms of simple design.
1. The nervous system is decentralized; there is no brain.
2. The unique water-vascular system operates the tube feet which have suction disks
that can be used in locomotion and prey capture.
3. Sea stars can evert their stomachs when feeding.
16.8 Evolutionary Trends Among Vertebrates
A. All chordates, at some time in their lives, have four distinctive features:
1. A notochord is a long rod of stiffened tissue that supports the body; later it changes to
bony units in vertebrates.
2. A dorsal, tubular nerve cord lies above the notochord and gut.
3. Embryos have gill slits in the wall of the pharynx.
4. A tail, or rudiment thereof, exists near the anus.
B. Early Craniates
1. Tunicates and lancelets do not have a cranium or vertebrae.
2. All other chordates are craniates.
a. The earliest ones resembled lamprey—modern fishes without jaws.
b. These were followed by ostracoderms—still jawless but with hardened external
plates
c. Placoderms were the first fishes with jaws and paired fins; they were replaced by
cartilaginous and bony fishes.
C. The Key Innovations
1. The single, continuous notochord was replaced by a column of separate, hardened
vertebrae, parts of which became modified near the head to form jaws.
2. Jaws allowed new feeding possibilities, coupled with better eyes for detecting both
prey and predators.
3. The fins of fishes were the starting point for the legs, arms, and wings seen among
higher vertebrates.
4. Gradually, there was less reliance on gills and more on lungs and the circulatory
system (heart, blood vessels), which works in connection.
16.9 Major Groups of Jawed Fishes
A. Enormous numbers of fishes attest to their success in meeting the challenges of life in the
water.
1. Their streamlined bodies allow easy movement through the dense medium.
2. Tail muscles are organized for powerful force.
3. The swim bladder provides buoyancy.
B. Cartilaginous fishes possess a streamlined body with a cartilaginous endoskeleton, gill
slits, fins, and small scales on the body surface.
1. This group includes the sharks and rays.
2. Sharks are formidable predators with their powerful jaws and teeth (replaceable).
C. Bony fishes are the most numerous and diverse vertebrates.
1. Ray-finned fishes have highly maneuverable fins supported by rays that originate
from the dermis.
2. The lobe-finned fishes, such as the coelacanths, bear fleshy extensions on the body.
3. Lungfishes have gills and one or a pair of "lungs" that are modified gut wall
outpouchings.
16.10 Early Amphibious Tetrapods
A. Amphibians have a body plan and mode of reproduction somewhere between "fishes"
and "reptiles."
1. Life on land presented new challenges to the emerging amphibians.
a. Water availability was not reliable.
b. Air temperatures were variable, and air itself was not the strong supporting
medium that water was, but it was a richer source of oxygen.
c. New habitats, including vast arrays of plants, necessitated keener sensory input.
2. Existing amphibians share several common characteristics:
a. All have bony endoskeletons and usually four legs.
b. Depending on their habitat, amphibians can respire by use of gills, lungs, skin,
and pharyngeal lining.
c. The skin is usually thin and sometimes supplied with glands that produce toxins.
B. Even though most amphibians are aquatic, none has escaped the water entirely for they
must return to it to lay eggs, which will produce larvae dependent on a watery
environment.
16.11 The Rise of Amniotes
A. The “Reptiles”
1. Four features were critical to amniotes' escape from water dependency:
a. The produce amniote eggs with covering membranes and a shell, which allow the
eggs to laid in dry habitats.
b. Amniotes have a toughened, dry, or scaly skin that is resistant to drying.
c. They have a copulatory organ that permits internal fertilization.
d. Their kidneys are good at conserving water.
2. "Reptiles" demonstrate certain advantages features compared to amphibians.
a. Modification of limb bones, teeth, and jawbones allowed greater exploitation of
the insect life emerging in the Late Carboniferous.
b. Development of the cortex region of the cerebrum permitted greater integration of
sensory input and motor response.
c. A four-chambered heart and more efficient lungs allowed greater activity.
3. Early reptiles gave rise to the dinosaurs.
a. The first dinosaurs probably were small, warm-blooded creatures who thrived in
the adaptive zones opened to them as the results of asteroid impacts about 213
million years ago.
b. The monstrous dinosaurs that we all recognize in pictures and movies dominated
life on Earth until the mass extinction proposed by the K-T asteroid impact theory
about 65 million years ago.
c. Their fact was sealed by the unbearably hot conditions created, according to the
global broiling hypothesis.
d. Present-day crocodilians, turtles, tuatuaras, snakes, and lizards are what’s left of
this group.
B. The Birds
1. Birds can fly because of several adaptations:
a. Feathers covering the wings make a good flight surface and conserve metabolic
heat
b. Bones in the bird body are lightweight because of air cavities within them.
c. The heart is four-chambered, and the lungs are highly efficient because of their
“flow-through” design.
d. Powerful muscles are attached at strategic places on the bones for maximum
leverage.
2. Birds are incredibly diverse in color, courtship, song, and size, including the very
large flightless ones such as the ostrich.
C. The Rise of Mammals
1. Mammals evolved before dinosaurs and outlasted them.
a. By Jurassic times, mouse-sized therians with jaws and hair had evolved.
b. With the demise of the dinosaurs, diverse adaptive zones opened up for egglaying mammals (monotremes), pouched mammals (marsupials), and placental
mammals (eutherians).
2. Mammals are characterized by the following:
a. Hair covers at least part of the body (whales are an exception).
b. Milk-secreting glands nourish the young.
c. Four different types of teeth (incisors, canines, premolars, and molars) in the
mammalian mouth are specialized to meet dietary habits.
d. Brain capacity is increased, allowing more capacity for memory, learning,
conscious thought, and behavioral flexibility.
16.12 From Early Primates to Humans
A. Primates include a wide variety of animals:
1. Prosimians (literally: before apes) are small tree dwellers (arboreal) that use their
large eyes to advantage during night hunting.
2. Tarsiers (tarsioids) are small primates with features intermediate between prosimians
and anthropoids.
3. Anthropoids include monkeys, apes, and humans.
a. Hominoids include apes and humans.
b. Hominid refers to human lineages only.
B. Primate evolution displays key trends:
1. Enhanced daytime vision:
a. Early primates had an eye on each side of the head.
b. Later ones had forward-directed eyes resulting in better depth perception and
increased ability to discern shape, movement, color, and light intensity.
2. Upright walking:
a. Bipedalism is possible because of skeletal reorganization in primates ancestral to
humans.
b. A monkey skeleton is suitable for a life of climbing, leaping, and running along
tree branches with palms down.
c. An ape skeleton is suitable for climbing and using the arms for carrying some
body weight; the shoulder blades allow the arms to swivel overhead.
d. Humans have a shorter, S-shaped, and somewhat flexible backbone.
3. Power grip and precision grip:
a. Prehensile movements allowed fingers to wrap around objects in a grasp.
b. Opposable thumb and fingers allowed more refined use of the hand.
c. The precision and power grip movements of the human hand allowed for toolmaking.
4. Teeth for all occasions:
a. Monkeys have rectangular jaws and long canines.
b. Humans have a bow-shaped jaw and smaller teeth reflecting the changes in diet.
5. Brain, behavior, and culture:
a. Brain expansion and elaboration produced a brain of increased mass and
complexity, especially for thought, language, and conscious movements.
b. Human brain development led to patterns of human behavior known collectively
as culture.
C. Origins and Early divergences
1. The first primates that evolved from mammals about 60 million years ago (Paleocene)
resembled small rodents or tree shrews; they had long snouts and were good foragers
on the forest floor.
2. By the Eocene, their descendants were living in trees, had larger brains, were active in
the daytime, and possessed better grasping movements.
3. By the time of the Oligocene, tree-dwelling ancestors of monkeys and apes, had
emerged.
4. The first hominoids appeared between 23 and 5 million years ago (Miocene).