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•
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19.1 Evolution of Animals
19.1.1 Explain how animals are distinguished from other groups of organisms.
19.1.2 Explain how the evolutionary tree of animals is constructed.
19.2 Introducing the Invertebrates
19.2.1 Describe the evolutionary trends among sponges, cnidarians, flatworms, and roundworms.
19.2.2 Give examples of flatworms and roundworms that adversely affect human health.
19.3 Protostomes and Deuterostomes Compared
19.3.1 Distinguish between protostomes and deuterostomes.
19.4 Molluscs, Annelids, and Arthropods
19.4.1 Recognize the common characteristics of molluscs, annelids, and arthropods.
19.4.2 Describe the defining characteristics of molluscs, annelids, and arthropods, and give
examples of each.
19.4.3 Explain why arthropods are such a successful group.
19.5 Echinoderms and Chordates
19.5.1 Recognize the common characteristics of echinoderms and chordates.
19.5.2 Describe the defining characteristics of echinoderms.
19.5.3 Describe the defining characteristics of the invertebrate and vertebrate chordates.
19.5.4 Describe the defining characteristics of each group of vertebrates: fishes, amphibians,
reptiles, and mammals.
19.6 Human Evolution
19.6.1 Explain how the evolutionary tree of primates is constructed.
19.6.2 Describe evolutionary trends among the hominins.
19.6.3 Summarize the two major hypotheses for the evolution of modern humans.
19.1 Evolution of animals
•
Animals are multicellular eukaryotes.
•
•
Like plants and fungi
Animals are chemoheterotrophs.
•
•
•
Unlike autotrophic plants
Like fungi but animals ingest food and digest
internally while fungi digest food externally
Animals usually carry on sexual reproduction.
•
•
•
Begin life as a fertilized diploid egg
Undergo developmental changes
Organism with specialized tissues
• Muscle and nerve tissue characterize animals.
• Ancestry of animals
 Colonial flagellate hypothesis
• Animals descended from an ancestor that
resembled a hollow spherical colony of
flagellated cells.
• Implies radial symmetry preceded bilateral
symmetry as the evolutionary tree of
animals predicts
• Among protists,
choanoflagellates most
likely resemble the last
unicellular ancestor of
animals.
Figure 19.3
Choanoflagellate
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or
display.
 Supported by molecular
single cell
data
stalk
• Evolutionary tree of animals
 Based on molecular data and developmental
stages
 Trends
• Multicellularity
• 2 or 3 true tissues associated with 2 germ layers in
embryos
• Symmetry – radial vs. bilateral
 Bilateral organisms with cephalization
• Protostome vs. deuterostome
 Protostomes can be acoelomate, pseduocoelomates or
coelomates.
 Deuterostomes are coelomates.
• Segmentation – leads to specialization
• Symmetry
 Radial symmetry – animal is organized
circularly
 Bilateral symmetry – animal has right and
left halves
• Accompanied by cephalization – localization
of brain and specialized sensory organs at
the anterior end of animal
• Coelom – body cavity
 Acoelomate – no body cavity
• Packed solid with mesoderm
 Pseudocoelomates – body cavity
incompletely lined with mesoderm
 Coelomate – body cavity completely
lined with mesoderm
• Mesentery supports internal organs.
• Body movements are freer because outer
wall can move independently of organs.
• Organs have more space to become
complex.
• In animals without a skeleton, the coelom
acts as a hydrostatic skeleton.
19.2 Introducing the invertebrates
• Sponges: Multicellularity
 Saclike bodies with many pores
 Aquatic, largely marine
 Multicellular but lack organized tissues
• Cellular level of organization
 Interior of sponge lined with flagellated collar cells or
choanocytes
 Filter feeder – filters food out of water using pores
and collar cell microvilli
 Reproduce sexually or asexually
• Asexual fragmentation or budding
• Cnidarians: True Tissues
 Rich fossil record
 Radially symmetrical
 Capture prey using ring of tentacles with
cnidocytes
• Cnidocyte contains nematocyst that may trap,
penetrate or inject toxin
 Aquatic, mostly marine
 2 germ layers – ectoderm and endoderm
• Tissue level of organization
 2 basic body forms
• Polyp – mouth directed upward from substrate
• Medusa – mouth directed downward
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 19.9 More
cnidarians
float
a. Portugese man-of-war
is a colony of poly and
medusa type
individuals.
b. Coral have polyps as
the dominant life stage.
c. Jellyfish have medusa
as the dominant life
stage.
polyp
tentacles
fish
a. Portuguese man-of-war
b. Cup coral
c. Jellyfish
a: © Runk/Schoenberger/Grant Heilman Photography; b: © Ron Taylor/Bruce Coleman; c: © Under Watercolours
• Flatworms: Bilateral Symmetry
 Have 3 germ layers
 Acoelomate
 Planarians are free-living flatworms.
• Several body systems including a nervous system
• Cephalization – brain, eyespots and
chemosensitive organs on head
• Incomplete digestive system – only 1 opening
 Muscular pharynx
• Hermaphrodites
 Both male and female sex organs
 Cross-fertilize
• Flatworms (cont.)
 Parasitic flatworms
• Tapeworms
 Endoparasites
 Vary in size up to 20 meters
 Scolex used to attach to host
• Flukes




Endoparasites
Oral sucker and another sucker
Named for organ they inhabit
Nearly 800,000 people die from blood fluke
(Schistosoma) infections.
• Roundworms: Pseudocoelomates
 2 features not yet seen to this point
1. Body cavity – pseudocoelom
• Incompletely lined with mesoderm
2. Complete digestive tract
• Both mouth and anus
 Nonsegmented
 Occur almost everywhere – sea, fresh water,
soil
 Free-living or parasitic
 Ascaris (intestinal), Trichinosis (skeletal
muscle), Elaphantiasis (lymphatic vessels),
pinworms, hookworms
19.3 Protostomes and
Deuterostomes Compared
• Protostomes
 Flatworms, roundworms, molluscs, annelids,
arthropods
• Deuterostomes
 Echinoderms and chordates
• Distinguished based on embryological
development
 Cell division pattern is different
• First embryonic opening is called blastopore.
 In protostomes becomes mouth
 In deuterostomes becomes anus
19.4 Molluscs, Annelids,
and Arthropods
•
•
All are protostomes with a coelom.
Molluscs

All molluscs have a body with at least 3
parts.
1. Visceral mass – internal organs
2. Foot – muscular portion used for locomotion
3. Mantle – envelopes but does not enclose visceral
mass


May secrete shell
Radula – tongue like with many teeth
• 3 classes of molluscs: Gastropods,
Cephalopods, Bivalves
1. Gastropods
• Nudibranchs, conchs, and snails
• Herbivores or carnivores
• Terrestrial snails use mantle as lung.
2. Cephalopods
•
•
•
•
Octopuses, squids, and nautiluses
Foot evolved into tentacles around head
Well-developed nervous system
Complex sensory organs
3. Bivalves
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•
•
Clams, oysters, scallops, and mussels
2 parts to the shell
Filter feeders
• Annelids
 Segmented – can be seen externally in rings
encircling body
 Septa divide fluid-filled coelom.
• Used as hydrostatic skeleton
 Complete digestive tract with specialized parts
• Pharynx, esophagus, crop, gizzard, intestine
 Extensive closed circulatory system
 Nervous system has brain and ventral nerve cord.
• Ganglia in each segment
 Nephridia in excretory system
• Nephridium collects waste and excretes it through pore in
body wall.
• Annelids
Figure 19.17 Other annelids
 Polychaetes
• Have many setae per
segment
spiraled
tentacles
• Nereis is a predator.
• Other are sedentary setae
filter feeders.
a. Clam worm
b. Christmas tree worm
 Oligochaeates
• Few setae per segment
• Earthworms
• Scavengers in dirt
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a: © Heather Angel; b: © James Carmichael/Nature Photographics
Figure 19.17 continued
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
anterior
sucker
posterior
sucker
 Leeches
•
•
•
•
c. Medicinal leech
© St. Bartholomews Hospital/Photo Researchers, Inc.
No setae
Most freshwater but some marine or terrestrial
Some free-living but most are fluid feeders
Hirudin is a powerful anticoagulant.
•
Arthropods

Extremely diverse – over 1 million species
•

As many as 30 million may exist
Success due to 6 characteristics
1.
2.
3.
4.
5.
6.
Jointed appendages – modifications
Exoskeleton – made of chitin, must be molted
Segmentation – repeating body units
Well-developed nervous system
Variety of respiratory organs
Reduced competition through metamorphosis

Larvae and adult may have different lifestyle.
Figure 19.20 Crustacean diversity
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a.
d.
b.
c.
a: © Kim Taylor/Bruce Coleman; b: © James Carmichael/Nature Photographics; c: © Natural History Photographic Agency; d: © Kjell
Sandved/Butterfly Alphabet
• Arthropods
 Crustaceans – barnacles, shrimp, lobsters, crabs,
crayfish, pillbugs
• Head and thorax fused into cephalothorax
• Pair of compound eyes
• Gills above walking legs
• Arthropods
Figure 19.21 More arthropods
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
 Arachnids
• Spiders, scorpions, ticks,
mites, and harvestmen
(“daddy long legs”)
• Spiders
a.
 Narrow waist separates
cephalothorax from abdomen.
 Inject venom and digest food
externally before sucking it up
 Book lungs
• Scorpions
 Oldest terrestrial arthropods
 Nocturnal
b.
a: © C. Allan Morgan/Peter Arnold; b: © John Bell/Bruce Coleman
Figure 19.21 continued
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
e
c
• Arthropods
d.
c(ventral): © Daniel Lyons/Bruce Coleman; c(dorsal): © Ken Lucas/Ardea; d: © David M. Dennis/Animals Animals; e:
© Geof de Feu/Imagestate
• Mites and ticks are parasites.
 Chiggers are larvae of certain mites.
• Horseshoe crabs
 First pair of appendages pincerlike
 Great interest to medical sciences
• Centipedes – 1 pair of appendages per segment
 Carnivorous
• Millipedes – 2 pairs of appendages per segment
 Herbivorous
• Arthropods
 Insects
• Very numerous and diverse
• Entomology – study of insects
• Adapted to active life on land
 Some have secondarily invaded aquatic habitats
•
•
•
•
Body – head, thorax, abdomen
Mouthparts adapted to particular way of life
3 pairs of legs
1 or 2 pairs of wings (or none)
19.5 Echinoderms and Chordates
• Both deuterostomes
• Echinoderms
 Larva is free-swimming filter feeder with bilateral
symmetry.
 Adults are radially symmetric without a head, brain or
segmentation.
• Nerve ring around mouth extends outward
 Locomotion depends on water vascular system.
• Water enters through sieve plate
• Pumped into tube feet – like suction cups
 No complex respiratory, excretory, or circulatory
system
• Fluids in coelomic cavity and water vascular system do this
•
Chordates

At some time in their life history, a
chordate has 4 characteristics.
1. Dorsal supporting rod called notochord

Vertebrates have an endoskeleton of cartilage or
bone.
2. Dorsal tubular nerve cord
3. Pharyngeal pouches
4. Postanal tail
• Invertebrate chordates
Figure 19.25 Invertebrate
chordates
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
 Notochord never replaced
by vertebral column
 Tunicates
• “Sea squirts” can squirt
water from siphon when
disturbed.
• Larva is bilaterally
symmetrical and has 4
chordate characteristics.
• Metamorphosis produces
a.
sessile adult which retains
only gill slits of 4
characters.
© Rick Harbo
Copyright © The McGraw-Hill Companies, Inc. Permission required for
reproduction or display.
b.
Figure 19.25 continued
© Heather
Angel
• Invertebrate chordates
 Lancelets
•
•
•
•
•
Marine chordates a few cm long
Found in shallow water buried in sand
Filter feeder
Retain 4 chordate characteristics as adults
Segmentation is present – muscle and nerve cord
• Evolutionary trends among the chordates
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
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
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Presence of vertebrae
Jaws
Lungs
Jointed appendages
Amniotic egg
• Fishes: First jaws and lungs
 First vertebrates were jawless fishes.
 3 living classes of fishes
1. Jawless
2. Cartilaginous
3. Bony
 2 latter groups have jaws
• Believed to have evolved from first pair of gill
arches
• Jawless fishes
Figure 19.28 Diversity of fishes
 Cylindrical and up to a
meter long
toothed oral disk
 Smooth, scaleless skin gill slits
(seven pairs)
 No jaws or paired fins
 Hagfish are scavengers.
 Some lampreys are
parasites.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a. Lamprey , a jawless fish
•
Cartilaginous fish



Figure 19.28 continued
Sharks, skates and rays
Skeletons of cartilage
not bone
3 well-developed
senses enable sharks
and rays to detect prey.
1. Sense electric currents in
water
2. Lateral line system
3. Keen sense of smell
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or
display.
dorsal fin
gill slits
(five pairs)
jaw with
teeth
b. Bull shark, a cartilaginous fish
pectoral fin
© Heather Angel; : © Ingram Publishing/Alamy RF
• Bony fish
 Most numerous and
diverse of all
vertebrates
 Ray-finned fishes – fins
supported by bony
spikes
• Perch, trout, salmon,
haddock, etc.
• Filter feeders,
opportunists, or predators
• Swim bladder serves as
buoyancy organ.
 Can change density of
gases to go up or
down in water
• Single-circuit circulatory
system
 Nondivided atrium and
ventricle
Figure 19.28 continued
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or
display.
caudal fin anal fin second dorsal finfirst dorsal fin
gill slit
(one pair)
operculum
(covering
for gills)
pectoral fin
pelvic fin
c. Soldierfish, a bony fish
© Ron & Valerie Taylor/Bruce Coleman
Lobe-finned fishes
•Most had a lung for respiration
•Evolved into amphibians
•A shift in the position of the bones in
the forelimbs and hind limbs lifts and
supports the body.
• Amphibians: Jointed Vertebrate Limbs
 Frogs, toads, newts, and salamanders
 Features not seen in bony fish…
•
•
•
•
•
Jointed limbs
Eyelids
Ears
Voice-producing larynx
Larger brain
 Adults usually have small lungs.
• Air enters through mouth and is forced into
lungs.
• Supplemental gas exchange through moist
skin
 3 chambered heart
• Mixed blood sent to all parts of body
• Blood sent to skin – further oxygenated
 Larval stage lives in water; adults live on
land.
• Adult usually returns to water to reproduce.
• Reptiles: Amniotic Egg
 Diversified and were most abundant between 245 and
66 MYA
• Including ancestor to today’s mammals
• Bipedal stance of some reptiles preadaptive for evolution of
wings in birds





Turtles, crocodiles, snakes, and lizards
Body covered in scales
Use tongue as sense organ
Well-developed lungs
4 chambered heart – division incomplete in some
species
• Most outstanding adaptation is amniotic
egg
 Eliminated need for swimming larval stage
 Provides developing embryo with oxygen,
food, water, removes nitrogenous waste, and
protects embryo
• Uses extraembryonic membranes
 Ectothermic – body temperature matches
outside environment
• Fishes, amphibians, and reptiles
• Must move to warmer or cooler area to regulate
temperature
• Birds
 Share common ancestor with crocodiles
 Traits show they are reptiles
• Tail with vertebrae, clawed feet, scales
• Feathers are modified reptilian scales
 Exact history still in dispute
 Endotherms – generate internal heat
 Nearly every anatomical feature related to flight
•
•
•
•
•
•
•
Forelimbs modified into wings
Hollow, light bones laced with air cavities
Horny beak instead of heavy jaws
Slender neck and compact torso
Efficient respiration using air sacs
Completely separated 4-chambered heart
Acute vision and well-developed brains
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Traditional
classification
based in beak
and foot type
Figure 19.33 Bird’s beaks
A cardinal’s beak
allows it to crack
tough seeds.
a.
b.
c.
A flamingo’s beak
strains food from
the water with
bristles that fringe
the mandibles.
A bald eagle’s beak
allows it to tear prey
apart.
a: © Kirtley Perkins/Visuals Unlimited; b: © Thomas Kitchin/Tom Stack & Associates; c: © Brian Parker/Tom
Stack & Associates
• Mammals: Hair and Mammary Glands
 2 chief characteristics of mammals
• Hair – provides insulation against heat loss
• Mammary glands – enable female to feed
young without leaving them to find food
Figure 19.34
continued
Copyright © The McGraw-Hill Companies, Inc. Permission required for
reproduction or display.
b.
• Mammals
c.
b: © Leonard Lee Rue/Photo Researchers; c: © Fritz Prenzel/Animals Animals
 Marsupials
• Born in immature condition
• Newborns complete development inside female’s
pouch.
• Virginia opossum only marsupial north of Mexico
• Most Australian – koalas, kangaroos, Tasmanian wolf
 Placental mammals
• Vast majority of living mammals
• Extraembryonic membranes of amniote
egg modified for internal development
within uterus of female
• Adapted to active life on land
 Well developed brain – expansion of cerebral
hemispheres
 4 chambered heart
19.6 Human Evolution
•
•
•
•
All primates share a common ancestor.
Prosimians – lemurs, tarsiers, and lorises
Anthropoids – monkeys, apes, and humans
Primates adapted to arboreal life
 Mobile limbs
 Opposable thumbs and big toes
• Trend toward larger and more complex brain
• Evolutionary tree indicates humans most closely
related to African apes.
 Humans did not evolve from apes.
 Believed to share a common ancestor about 7 MYA
• Evolution of Hominins
 To be a hominin must have anatomy suitable
for standing erect and walking on 2 feet –
bipedal
• Hominid is a family designation for humans and
African apes.
 Early hominins
• Sahelanthropus tchadensis – dated to 7 MYA
 Braincase apelike, suggestions of bipedalism
• Ardipithecus ramidus – 4.5 MYA
 Only skull fragments
 Possibly bipedal
 Teeth intermediate between earlier apes and later
hominids
• Australopithecines
 Possibly direct
ancestor of humans
 In Africa about 4 MYA
 Australopithecus
afarensis – “Lucy”
Figure 19.38 Australopithecus
afarensis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Brain small (apelike)
but she stood upright
and walked bipedally
(humanlike)
• Trail of footprints
• Mosaic evolution – not
all body parts change
at the same rate
a.
b.
a: © Dan Dreyfus and Associates; b: © John Reader/Photo Researchers, Inc.
• Homo habilis







Dated between 2.0 and 1.9 MYA
May be ancestral to modern humans
45% larger brain than A. afarensis
Cheek teeth smaller – likely omnivorous
Stone tools
Enlarged portion of brain dealing with speech
Beginnings of culture – encompasses human
behavior and products and is dependent upon
capacity to speak and transmit knowledge
• Homo erectus






Found in Africa, Asia, and Europe
Dated between 1.9 and 0.3 MYA
Similar in appearance but may be several species
Larger brain and flatter face compared to H. habilis
Much taller
Robust and muscled skeleton still like
australopithecines
 Believed to have appeared in Africa and migrated into
Asia and Europe
 First to use fire
 Fashioned more advanced tools
• Evolution of modern humans
 Most researchers believe Homo sapiens
evolved from Homo erectus but details differ
 Multiregional continuity hypothesis
• Evolved separately in Asia, Africa, and Europe from
Homo erectus to Homo sapiens
• Opponents argue this is highly unlikely to evolve so
similarly in 3 widespread areas.
 Replacement model or out-of-Africa
hypothesis
•Homo erectus evolved to Homo sapiens only
in Africa and then migrated outward.
•Suggests we are more genetically similar
•Supported by research on human
mitochondrial DNA
• Neanderthals Homo neandertalensis
 Take name from German valley
 Possibly already present when Cro-Magnons showed
up
 Competition may have made Neanderthals go extinct
 Neanderthals had massive brow ridges.
 Nose, jaws, and teeth protruded far forward.
 Forehead low and sloping
 No chin
 Heavily muscled
 Sturdy build may have helped conserve body heat in
last Ice Age
 Culturally advanced
• Most lived in caves but may have built homes
• Variety of stone tools
• Buried dead with flowers and tools – religion?
• Cro-Magnons Homo sapiens
 Thoroughly modern appearance
 Advanced tools
 May have been first to make knifelike blades
and throw spears
• May be responsible for extinction of many larger
mammals like giant sloth, mammoth, sabertoothed tiger and giant ox
 Hunted cooperatively
 Perhaps first to have language
 Culture included art