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Deuterostomate Animals

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Title: Deuterostomate Animals


1
Deuterostomate Animals
2
Deuterostomate Animals
  • Deuterostome Ancestors
  • Echinoderms Pentaradial Symmetry
  • Hemichordates Conservative Evolution
  • Chordates New Ways of Feeding
  • Colonizing the Land Obtaining Oxygen from the
    Air
  • Birds More Feathers and Better Flight
  • The Origin and Diversity of Mammals
  • Primates and the Origin of Humans
  • Deuterostomes and Protostomes Shared
    Evolutionary Themes

3
Deuterostome Ancestors
  • A group of extinct animals known as the
    yunnanozoans are the likely ancestors of all
    deuterostomes.
  • These animals had a large mouth, six pairs of
    external gills, and a lightly cuticularized,
    segmented posterior body section.

4
Figure 34.1 The Ancestral Deuterostomes Had
External Gills
5
Deuterostome Ancestors
  • Modern deuterostomes fall into two major clades.
  • The echinoderms and hemichordates compose one
    clade.
  • This group is characterized by a three-part
    coelom and bilaterally symmetrical, ciliated
    larvae.
  • The other clade includes the chordates.
  • The ancestors of this clade had nonfeeding,
    tadpole-like larvae and a unique dorsal
    supporting structure.

6
Figure 34.2 A Current Phylogeny of the
Deuterostomes
7
Echinoderms Pentaradial Symmetry
  • Two major structural features evolved in the
    echinoderms (phylum Echinodermata).
  • One was a system of calcified internal plates
    covered by thin layers of skin and some muscles.
  • In some early echinoderm ancestors, these plates
    became fused inside the entire body, giving rise
    to an internal skeleton.
  • The other feature was a water vascular system, a
    network of calcified hydraulic canals leading to
    extensions called tube feet.
  • This system functions in gas exchange,
    locomotion, and feeding.

8
Figure 34.4 Echinoderms Display Two Evolutionary
Innovations (Part 1)
9
Figure 34.4 Echinoderms Display Two Evolutionary
Innovations (Part 2)
10
Echinoderms Pentaradial Symmetry
  • The development of these two structural
    innovations led to a striking evolutionary
    radiation.
  • There have been about 23 echinoderm classes
    described. Only 6 classes survive today, with a
    total of about 7,000 species.
  • Nearly all living species have a bilaterally
    symmetrical, ciliated larva that feeds for some
    time as a planktonic organism before transforming
    into an adult with pentaradial symmetry.
  • Living echinoderms are divided into two lineages
    the subphylum Pelmatozoa and the subphylum
    Eleutherozoa.

11
Echinoderms Pentaradial Symmetry
  • The arms are used for feeding. They are oriented
    in passing water currents so that food particles
    stick to tube feet on the arms, which transfer
    them to a groove that runs down the arm to the
    mouth.
  • Feather stars are similar to sea-lilies, but they
    have flexible appendages with which they grasp
    the substratum.

12
Figure 34.4 Diversity among the Echinoderms
(Part 1)
13
Echinoderms Pentaradial Symmetry
  • Most of the surviving echinoderms are members of
    the eleutherozoan lineage.
  • The sea urchins and the sand dollars (class
    Echinoidea) lack arms but they share a five-part
    body plan with all other echinoderms.
  • Sea urchins are hemispherical animals covered
    with spines attached to an underlying skeleton.
  • Sand dollars are flattened or disc-shaped animals
    that feed on algae and fragments of organic
    matter on the seafloor.

14
Figure 34.4 Diversity among the Echinoderms
(Part 2)
15
Echinoderms Pentaradial Symmetry
  • The class Holothuroidea, the sea cucumbers, have
    tube feet that are used primarily for attaching
    to a substrate rather than for moving.
  • They have anterior tube feet that are modified
    into tentacles used for feeding.
  • The body of sea cucumbers is oriented differently
    from other echinoderms. The mouth is anterior and
    the anus is posterior, not ventral and dorsal as
    in other echinoderms.

16
Figure 34.4 Diversity among the Echinoderms
(Part 3)
17
Echinoderms Pentaradial Symmetry
  • The sea stars (class Asteroidea) are the most
    familiar echinoderms.
  • Their tube feet serve as organs of locomotion and
    sites for gas exchange.
  • Tube feet are moved by expansion and contraction
    of circular and longitudinal muscles in the tube.
  • Sea stars are important predators in many marine
    environments, preying on polychaetes, gastropods,
    bivalves, and fishes.

18
Figure 34.4 Diversity among the Echinoderms
(Part 4)
19
Echinoderms Pentaradial Symmetry
  • The brittle stars (class Ophiuroidea) are similar
    in structure to the sea stars, but they have
    flexible arms that are composed of jointed hard
    plates.
  • Most feed by ingesting particles from the
    surfaces of sediments and assimilating the
    organic material from them, although some feed by
    capturing small animals.
  • Unlike most other echinoderms, they have only one
    opening to the digestive tract.

20
Figure 34.4 Diversity among the Echinoderms
(Part 5)
21
Chordates New Ways of Feeding
  • The phylum Chordata is the second major lineage
    of deuterostomes.
  • This phylum evolved several different
    modifications of the coelomic cavity that
    provided new ways for capturing and handling
    food.
  • They also evolved a different body plan
    characterized by an internal dorsal supporting
    structure.
  • The pharyngeal slits that originally served as
    sites for gas exchange and eliminating water
    became enlarged in the chordates.

22
Chordates New Ways of Feeding
  • Number of Species 49,530
  • Notable Features Bilateral symmetry complete
    gut coelomate.
  • Dorsal, hollow or tubular nerve cord
    cartilaginous notochord..
  • Pharyngeal gill slits.
  • Larval tunicates have nerve cord, notochord, tail
    and gill slits.
  • Adult forms retain only gill slits. Lancelets
    resemble larval sea squirts with the addition of
    myotomes (muscles).
  • In vertebrates the notochord is replaced by the
    vertebal column or backbone and there is cranial
    brain development.

23
Figure 34.7 Lancelets (Part 1)
24
Figure 34.7 Lancelets (Part 2)
25
Chordates New Ways of Feeding
  • In the lineage that gave rise to the vertebrates
    (subphylum Vertebrata), the enlarged pharyngeal
    basket came to be used to extract prey from mud.
  • The vertebrates have a jointed, dorsal vertebral
    column that replaced the notochord as their
    primary support.

26
Figure 34.8 A Current Phylogeny of the
Vertebrates
27
Chordates New Ways of Feeding
  • The following traits characterize the vertebrate
    body plan
  • A rigid internal skeleton, with the vertebral
    column as the anchor that provides support and
    mobility
  • Two pairs of appendages attached to the vertebral
    column
  • An anterior skull with a large brain
  • Internal organs suspended in a large coelom
  • A well-developed circulatory system, driven by
    contractions of a ventral heart

28
Figure 34.9 The Vertebrate Body Plan
29
Chordates New Ways of Feeding
  • Filter-feeding ancestral vertebrates lacked jaws
    and gave rise to the jawless fishes.
  • The ostracoderms were a group of jawless fishes
    that evolved a bony external armor that protected
    them from predators.
  • The hagfishes and the lampreys are the only
    jawless fishes (class Agnatha) to survive beyond
    the Devonian period. They have tough skins
    instead of external armor.
  • They lack paired appendages and have a round
    mouth that acts as a sucking organ by attaching
    to their prey and rasping at its flesh.

30
Figure 34.10 Modern Jawless Fishes (Part 1)
31
Figure 34.10 Modern Jawless Fishes (Part 2)
32
Chordates New Ways of Feeding
  • Many new kinds of fishes evolved during the
    Devonian period.
  • Members of one lineage evolved jaws from some of
    the skeletal arches that supported the gill
    region.
  • Jaws allowed fish to catch and subdue relatively
    large, living prey. The ability to chew aided in
    chemical digestion.

33
Figure 34.11 Jaws from Gill Arches
34
Chordates New Ways of Feeding
  • The cartilaginous fishes (class Chondrichthyes)
    became abundant during the Devonian period.
  • They include the sharks, skates and rays, and
    chimaeras.
  • They have a skeleton composed entirely of a firm
    but pliable material called cartilage.
  • Their skin is flexible and leathery the loss of
    external armor increased their mobility and their
    ability to escape from predators.

35
Figure 34.12 Cartilaginous Fishes (Part 2)
36
Chordates New Ways of Feeding
  • Pairs of unjointed appendages called fins control
    swimming.
  • These fins include the pectoral, pelvic, and
    dorsal fins.
  • Sharks move forward by means of their tail and
    pelvic fins.
  • Skates and rays propel themselves by means of
    undulating movements of their enlarged pectoral
    fins.
  • Nearly all cartilaginous fishes live in the
    oceans.

37
Figure 34.12 Cartilaginous Fishes (Part 1)
38
Chordates New Ways of Feeding
  • Class Osteichthyes - bony fish
  • Notable Features
  • Bony skeleton.
  • Bony operculum covering gill.
  • Two chambered heart swim bladder scales, mucous
    secretions to reduce friction.
  • Paired pectoral and pelvic fins

39
Chordates New Ways of Feeding
  • The early ray-finned fishes evolved gas-filled
    sacs to supplement the action of gills in
    respiration, enabling them to live in areas where
    oxygen was periodically in short supply.
  • In most species, these lunglike sacs evolved into
    swim bladders, which serve as organs of buoyancy.
  • Some fishes form large aggregations, called
    schools, in open waters.
  • Many species perform complex behaviors.

40
Figure 34.13 Diversity among Ray-Finned Fishes
(Part 1)
41
Figure 34.13 Diversity among Ray-Finned Fishes
(Part 2)
42
Figure 34.13 Diversity among Ray-Finned Fishes
(Part 3)
43
Figure 34.13 Diversity among Ray-Finned Fishes
(Part 4)
44
Colonizing the LandObtaining Oxygen from the Air
  • The evolution of lunglike sacs in response to the
    inadequacy of gills for respiration in
    oxygen-poor waters set the stage for the invasion
    of land.
  • Some bony fishes were able to supplement their
    gills with lung sacs when oxygen levels were low.
  • This ability allowed them to breathe air and to
    leave the water temporarily.

45
Colonizing the LandObtaining Oxygen from the Air
  • The amphibians (class Amphibia) arose during the
    Devonian period.
  • The jointed fins of their ancestors evolved into
    walking legs.
  • Finlike legs probably allowed Devonian
    predecessors of amphibians to crawl from one body
    of water to another.
  • Eventually they evolved the ability to live on
    dry land.
  • Most amphibian species have small lungs and
    exchange gases through their skin, and are
    confined to moist environments.

46
Colonizing the LandObtaining Oxygen from the Air
  • There are about 4,500 species of amphibians alive
    on Earth today.
  • The living amphibians are divided into three
    orders
  • Order - Caudata - Salamanders, Newts
  • Order Anura - Frogs, Toads
  • Class Reptilia - Reptiles
  • Most species live in water at some time in their
    lives.

47
Figure 34.15 Diversity among the Amphibians
(Part 1)
48
Figure 34.15 Diversity among the Amphibians
(Part 2)
49
Figure 34.15 Diversity among the Amphibians
(Part 3)
50
Colonizing the LandObtaining Oxygen from the Air
  • In a typical amphibian life cycle, adults spend
    part of all of their time on land, but return to
    fresh water to lay eggs.
  • Amphibian eggs can only survive in moist
    environments.
  • Fertilized eggs develop into larvae that live in
    water until they undergo metamorphosis to an
    adult.
  • Some amphibians are entirely aquatic, others
    entirely terrestrial.

51
Figure 34.16 In and Out of the Water
52
Colonizing the LandObtaining Oxygen from the Air
  • Two morphological changes contributed to the
    ability of one vertebrate lineage to control
    water loss and exploit a wider variety of
    terrestrial habitats
  • The evolution of an egg with a shell impermeable
    to water
  • A combination of traits that reduced water loss,
    such as skin that is impermeable to water and
    kidneys that could excrete concentrated urine
  • The vertebrates that evolved these traits are
    called amniotes.

53
Colonizing the LandObtaining Oxygen from the Air
  • Amniote eggs have a calcium-impregnated shell
    that prevents the evaporation of fluids inside
    but allows O2 and CO2 to pass through.
  • These eggs store large quantities of yolk that
    allow the embryo to attain a relatively advanced
    state of development before it hatches.

54
Figure 34.17 An Egg for Dry Places
55
Colonizing the LandObtaining Oxygen from the Air
  • The reptiles (class Reptilia) are an early
    amniote lineage that arose from the tetrapods
    during the Carboniferous period.
  • Although called a class, the reptiles are a
    paraphyletic group.
  • Some species have eggs that do not develop shells
    and are retained inside the females body until
    they hatch. Some of these species evolved
    placentas that nourish the developing embryos.
  • Reptiles have skin covered with horny scales that
    reduce water loss, exchange gas by the lungs, and
    have a heart divided into chambers that separate
    oxygenated from unoxygenated blood.

56
Figure 34.18 The Reptiles Form a Paraphyletic
Group
57
Figure 34.19 Reptilian Diversity (Part 1)
58
Colonizing the LandObtaining Oxygen from the Air
  • The subclass Squamata includes lizards, snakes,
    and the amphisbaenians, a group of legless
    burrowing animals with greatly reduced eyes.
  • The tuataras (subclass Sphenodontida) are a
    sister group to the lizards. This group was
    diverse in the Mesozoic, but only two species
    exist today.
  • Sphenodontids resemble lizards but differ in
    anatomical features.

59
Figure 34.19 Reptilian Diversity (Part 2)
60
Colonizing the LandObtaining Oxygen from the Air
  • The crocodilians (subclass Crocodylia) are
    confined to tropical and warm temperate
    environments.
  • They spend much of their time in water but build
    nests on land or on floating piles of vegetation.
  • Order Chelonia - turtles, tortoises

61
Figure 34.19 Reptilian Diversity (Part 3)
62
Colonizing the LandObtaining Oxygen from the Air
  • The dinosaurs dominated terrestrial environments
    from 215 mya until about 65 mya.
  • The ability to breathe and run simultaneously was
    a major innovation in the evolution of
    terrestrial vertebrates.
  • In the lineages leading to the mammals,
    dinosaurs, and birds, the legs assumed a vertical
    position.
  • Muscles that enabled the lungs to be filled and
    emptied while the limbs moved also evolved.
  • These muscles are present in living birds and
    mammals, and their existence can be inferred in
    dinosaurs from their fossils.

63
Colonizing the LandObtaining Oxygen from the Air
  • Dinosaur fossils recently discovered in China
    show that in some small predatory dinosaurs, the
    scales had been highly modified to form feathers.
  • Microraptor gui had feathers on all four limbs,
    very similar in structure to modern bird feathers.

64
Figure 34.20 Mesozoic Birds and Their Ancestors
(Part 1)
65
Birds More Feathers and Better Flight
  • A dinosaur lineage gave rise to the birds
    (subclass Aves) during the Mesozoic era.
  • The oldest known avian fossil is Archaeopteryx,
    (150 mya) which had feathers virtually identical
    to those of modern birds.
  • Archaeopteryx also had well-developed wings, a
    wishbone, and typical perching bird claws.
  • Another early bird known only from fossils is
    Confuciuornis sanctus fossilized remains were
    discovered in 120125-million-year-old fossil
    beds in China.

66
Figure 34.20 Mesozoic Birds and Their Ancestors
(Part 2)
67
Figure 34.20 Mesozoic Birds and Their Ancestors
(Part 3)
68
Birds More Feathers and Better Flight
  • Most paleontologists believe that birds evolved
    from terrestrial bipedal dinosaurs that used
    their forelimbs for capturing prey.
  • These dinosaurs may have initially developed
    feathers for insulation or display, and
    eventually were able to become airborne for short
    distances.
  • There are about 9,600 species of birds today,
    ranging in size from the 2-gram bee hummingbird
    to the 150-kilogram ostrich.

69
Class Aves
  • Class Aves - Birds
  • Notable Features
  • Four chambered heart.
  • Scales modified into feathers.
  • Internal fertilization.
  • Hard amniotic eggs.
  • Wings.
  • Endothermic.
  • Hollow bones

70
Figure 34.21 Diversity among the Birds (Part 1)
71
Figure 34.21 Diversity among the Birds (Part 2)
72
Figure 34.21 Diversity among the Birds (Part 3)
73
Figure 34.21 Diversity among the Birds (Part 4)
74
Birds More Feathers and Better Flight
  • As a group, birds eat almost all types of animal
    and plant material.
  • They serve as a major agent of seed dispersal by
    eating the seeds of plants.
  • Feathers function not only in flight, but also in
    thermoregulatory and display functions.
  • The bones of birds are modified for flight they
    are hollow and have internal struts for strength.
  • The breastbone forms a large, vertical keel to
    which pectoral muscles are attached. These
    muscles pull the wings downward during the
    propulsive movement in flight.

75
Birds More Feathers and Better Flight
  • Flight is metabolically expensive, and thus birds
    have very high metabolic rates.
  • As a consequence, they generate large amounts of
    heat, whose loss is controlled by feathers that
    can trap or release warm air.
  • Birds have an enlarged cerebellum, the center of
    sight and muscular coordination.
  • Most birds lay eggs in a nest, where the young
    are usually cared for by the parents after
    hatching.

76
The Origin and Diversity of Mammals
  • Mammals (class Mammalia) appeared in the early
    part of the Mesozoic era.
  • Notable Features
  • Four chambered heart.
  • Fur or hair.
  • Internal fertilization.
  • Mammary glands.
  • Endothermic
  • Small mammals coexisted with reptiles and
    dinosaurs for at least 150 million years.
  • Todays mammals range in size from tiny shrews
    and bats that weigh only 2 grams to the
    endangered blue whale, which can measure up to 33
    meters long and weigh up to 160,000 kilograms.

77
The Origin and Diversity of Mammals
  • Skeletal modifications accompanied the evolution
    of the small mammals from their larger reptilian
    ancestors
  • Bones from the lower jaw were incorporated into
    the middle ear, leaving a single bone in the
    lower jaw.
  • The number of bones in the skull was decreased.
  • The bulk of the limbs and the bony girdles from
    which they are suspended were reduced.
  • Mammals have fewer teeth than reptiles, but
    mammal teeth are more differentiated.

78
The Origin and Diversity of Mammals
  • Skeletal features are readily preserved as
    fossils, so these developments can be traced in
    the fossil record.
  • Soft parts of animals are seldom fossilized
    thus, it is difficult to tell when mammalian
    features such as mammary glands, sweat glands,
    hair, and a four-chambered heart evolved.
  • The mammals are unique in providing their young
    with milk secreted by mammary glands.
  • Mammalian eggs are fertilized within the females
    body, and prior to birth, embryos undergo a
    period of development called gestation within a
    uterus.

79
The Origin and Diversity of Mammals
  • The approximately 4,000 species of living mammals
    are divided into two major subclasses
    Prototheria and Theria.
  • The subclass Prototheria contains a single order,
    the Monotrema, which contains only three species.
  • The monotremes differ from other mammals in that
    they lack a placenta, lay eggs, and have legs
    that poke out to the side.

80
Figure 34.22 Monotremes
81
The Origin and Diversity of Mammals
  • Two major groups of mammals, the marsupials and
    the eutherians, are members of the subclass
    Theria.
  • Females of the group Marsupialia have a ventral
    pouch in which they carry and feed their
    offspring.
  • Gestation in marsupials is short early stages of
    offspring development take place in the pouch.
  • There are about 240 living species of marsupials.

82
Figure 34.23 Marsupials (Part 1)
83
Figure 34.23 Marsupials (Part 2)
84
The Origin and Diversity of Mammals
  • Most living mammals are eutherians.
  • Eutherians are more highly developed at birth
    than marsupials, and no external pouch houses
    them after birth.
  • There are about 4,000 living species of
    eutherians in 16 different groups.

85
Figure 34.24 Diversity among the Eutherians
(Part 1)
86
Figure 34.24 Diversity among the Eutherians
(Part 2)
87
Figure 34.24 Diversity among the Eutherians
(Part 3)
88
Primates and the Origin of Humans
  • Humans belong to another eutherian lineage, the
    primates.
  • The primates likely descended from small
    tree-living insectivores during the Cretaceous
    period.
  • A nearly complete fossil found in Wyoming of an
    ancient primate species, Carpolestes, dates to 56
    mya.
  • This early primate had grasping feet with an
    opposable big toe that had a nail rather than a
    claw.
  • These grasping limbs are one of the major
    adaptations that distinguish primates from other
    animals.

89
Primates and the Origin of Humans
  • The primate lineage split into two main branches
    early in its evolutionary history the prosimians
    and the anthropoids.
  • The prosimians include the lemurs, pottos, and
    lorises.
  • The mainland prosimian species are arboreal and
    nocturnal.
  • Diurnal and terrestrial prosimian species are
    present on the island of Madagascar.

90
Figure 34.25 A Current Phylogeny of the Primates
91
Figure 34.26 Prosimians
92
Primates and the Origin of Humans
  • The anthropoids include the tarsiers, monkeys,
    apes, and humans.
  • They evolved from an early primate lineage about
    55 mya in Africa or Asia.
  • The New World monkeys probably reached South
    America from Africa when those two continents
    were still touching.
  • All New World monkeys are arboreal many having
    long, prehensile tails.
  • Old World monkeys are terrestrial and arboreal,
    but none have prehensile tails. They often live
    in social groups.

93
Figure 34.27 Monkeys
94
Primates and the Origin of Humans
  • About 22 mya, the lineage leading to modern apes
    separated from other Old World primates.
  • About 9 mya, members of one European ape lineage
    migrated to Africa and became ancestors of modern
    African apes and of humans.

95
Figure 34.28 Apes (Part 1)
96
Figure 34.28 Apes (Part 2)
97
Primates and the Origin of Humans
  • The hominids separated from other ape lineages
    about 6 mya in Africa.
  • The earliest protohominids are known as the
    ardipithecines.
  • These apes had morphological adaptations for
    bipedalism.
  • Bipedal locomotion frees the hands to manipulate
    objects and carry them while walking.
  • It also elevates the eyes, enabling animals to
    spot predators and prey.
  • Bipedal movement is more energetically economical
    than quadruped movement.

98
Primates and the Origin of Humans
  • The ardipithecines gave rise to the
    australopithecines.
  • The most complete fossil skeleton of an
    australopithecine was discovered in Ethiopia in
    1974 and is known as Lucy.
  • Lucy is about 3.5 million years old and belongs
    to the species Australopithecus afarensis.
  • Experts disagree over how many species are
    represented by the different australopithecine
    fossils that have been found, but it is clear
    that at least two distinct types lived together
    over much of eastern Africa.

99
Primates and the Origin of Humans
  • Early hominidsmembers of the genus Homolived
    contemporaneously with australopithecines for
    about a half million years.
  • The oldest fossils belong to the extinct species
    Homo habilis, estimated to have lived about 2
    mya.
  • Homo erectus evolved in Africa about 1.6 mya and
    may have exterminated H. habilis.
  • H. erectus used fire and made tools that were
    probably used for digging, capturing animals,
    cleaning and cutting meat, scraping hides, and
    cutting wood.
  • H. erectus was replaced in tropical regions by
    Homo sapiens about 200,000 years ago.

100
Figure 34.29 A Current Phylogeny of Homo sapiens
101
Primates and the Origin of Humans
  • Large brain size evolved in the Homo lineage as
    social lives became increasingly complex.
  • The human brain has large amounts of omega-3 and
    omega-6 fatty acids, which cannot be synthesized
    they must be obtained from the diet.
  • Access to fat-rich foods from aquatic
    environments may have been the key factor that
    supported the expansion of the human brain.
  • The archeological record of the past 100,000
    years includes large piles of mollusk shells and
    fish bones, as well as carved points used for
    fishing, supporting this idea.

102
Primates and the Origin of Humans
  • Several Homo species existed during the
    mid-Pleistocene epoch and were skilled hunters of
    large mammals.
  • H. neanderthalensis was widespread in Europe and
    Asia between 75,000 and 30,000 years ago. They
    hunted large mammals and made a variety of tools.
  • Many scientists believe that they were
    exterminated by the H. sapiens known as the
    Cro-Magnons.
  • Cro-Magnon people spread across Asia and reached
    North America perhaps as early as 20,000 years
    ago.

103
Figure 34.30 Hunting Inspires Art
104
Primates and the Origin of Humans
  • The evolution of larger brains increased the
    behavioral capacity of our ancestors, especially
    the capacity for language.
  • Our expanded mental abilities are largely
    responsible for the development of culture, the
    process by which knowledge and traditions are
    passed from one generation to another by teaching
    and observation.
  • Cultural learning greatly facilitated the spread
    of domesticated plants and animals.
  • Human societies converted from those that were
    based on hunting and gathering to those that were
    pastoral and agricultural.

105
Deuterostomes and ProtostomesShared
Evolutionary Themes
  • Deuterostome evolution paralleled protostome
    evolution in several ways.
  • Both groups exploited abundant food in soft
    marine sediments attached to rock or suspended in
    water.
  • In lineages of both groups, the body became
    compartmentalized.
  • Planktonic larval stages evolved in both groups.
  • Both groups colonized the land, but the internal
    skeletons of deuterostomes were able to support
    much larger animals.
  • The terrestrial deuterostomes recolonized aquatic
    environments a number of times.
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