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Chapter 34. Vertebrates. Overview: Half a Billion Years of Backbones. Early in the Cambrian period, about 530 million years ago, an astonishing variety of animals inhabited Earth’s oceans One type of animal gave rise to vertebrates, one of the most successful groups of animals

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Chapter 34

Chapter 34

Vertebrates


Overview half a billion years of backbones
Overview: Half a Billion Years of Backbones

  • Early in the Cambrian period, about 530 million years ago, an astonishing variety of animals inhabited Earth’s oceans

  • One type of animal gave rise to vertebrates, one of the most successful groups of animals

  • The animals called vertebrates get their name from vertebrae, the series of bones that make up the backbone

  • There are about 52,000 species of vertebrates, including the largest organisms ever to live on the Earth

  • Vertebrates have great disparity, a wide range of differences within the group


Fig. 34-1

Are humans among the descendants of this ancient organism?

Myllokunmingia fengjiaoa (3 cm)


Fig. 34-2

Echinodermata

(sister group to chordates)

Cephalochordata

(lancelets)

ANCESTRAL

DEUTERO-

STOME

Chordates

Urochordata

(tunicates)

Notochord

Myxini

(hagfishes)

Common

ancestor of

chordates

Craniates

Petromyzontida

(lampreys)

Head

Vertebrates

Chondrichthyes

(sharks, rays, chimaeras)

Vertebral column

Actinopterygii

(ray-finned fishes)

Gnathostomes

Jaws, mineralized skeleton

Actinistia

(coelacanths)

Osteichthyans

Lungs or lung derivatives

Lobe-fins

Dipnoi

(lungfishes)

Lobed fins

Amphibia (frogs,

salamanders)

Tetrapods

Reptilia

(turtles, snakes,

crocodiles, birds)

Legs

Amniotes

Amniotic egg

Mammalia

(mammals)

Milk


Concept 34 1 chordates have a notochord and a dorsal hollow nerve cord
Concept 34.1: Chordates have a notochord and a dorsal, hollow nerve cord

  • Vertebrates are a subphylum within the phylum Chordata

  • Chordates are bilaterian animals that belong to the clade of animals known as Deuterostomia

  • Two groups of invertebrate deuterostomes, the urochordates and cephalochordates, are more closely related to vertebrates than to other invertebrates

  • All chordates share a set of derived characters

  • Some species have some of these traits only during embryonic development

  • Four key characters of chordates:

    • Notochord

    • Dorsal, hollow nerve cord

    • Pharyngeal slits or clefts

    • Muscular, post-anal tail


Fig. 34-3 hollow nerve cord

Dorsal,

hollow

nerve cord

Muscle

segments

Notochord

Mouth

Anus

Pharyngeal

slits or clefts

Muscular,

post-anal tail


Notochord
Notochord hollow nerve cord

  • The notochord is a longitudinal, flexible rod between the digestive tube and nerve cord

  • It provides skeletal support throughout most of the length of a chordate

  • In most vertebrates, a more complex, jointed skeleton develops, and the adult retains only remnants of the embryonic notochord

Dorsal Hollow Nerve Cord

  • The nerve cord of a chordate embryo develops from a plate of ectoderm that rolls into a tube dorsal to the notochord

  • The nerve cord develops into the central nervous system: the brain and the spinal cord


Pharyngeal slits or clefts
Pharyngeal Slits or Clefts hollow nerve cord

  • In most chordates, grooves in the pharynx called pharyngeal clefts develop into slits that open to the outside of the body

  • Functions of pharyngeal slits:

    • Suspension-feeding structures in many invertebrate chordates

    • Gas exchange in vertebrates (except vertebrates with limbs, the tetrapods)

    • Develop into parts of the ear, head, and neck in tetrapods

Muscular, Post-Anal Tail

  • Chordates have a tail posterior to the anus

  • In many species, the tail is greatly reduced during embryonic development

  • The tail contains skeletal elements and muscles

  • It provides propelling force in many aquatic species


Lancelets

Fig. 34-4 hollow nerve cord

Lancelets

Cirri

2 cm

Mouth

Pharyngeal slits

Atrium

Notochord

Digestive tract

Atriopore

Dorsal, hollow

nerve cord

Segmental

muscles

Anus

Tail

  • Lancelets (Cephalochordata) are named for their bladelike shape

  • They are marine suspension feeders that retain characteristics of the chordate body plan as adults


Fig. 34-5 hollow nerve cord

  • Tunicates (Urochordata) are more closely related to other chordates than are lancelets

  • They are marine suspension feeders commonly called sea squirts

  • As an adult, a tunicate draws in water through an incurrent siphon, filtering food particles

Incurrent

siphon

to mouth

Water flow

Notochord

Dorsal, hollow

nerve cord

Excurrent

siphon

Tail

Excurrent

siphon

Excurrent

siphon

Atrium

Muscle

segments

Incurrent

siphon

Pharynx

with

slits

Intestine

Anus

Stomach

Intestine

Tunic

Atrium

Esophagus

Pharynx with slits

Stomach

An adult tunicate

A tunicate larva

  • Tunicates most resemble chordates during their larval stage, which may last only a few minutes


Conceptual summary
Conceptual Summary hollow nerve cord

  • Vertebrates almost certainly evolved from a tadpole-lie invertebrate larva that failed to metamorphose but became sexually mature


Concept 34 2 craniates are chordates that have a head
Concept 34.2: Craniates are chordates that have a head hollow nerve cord

  • The origin of a head opened up a completely new way of feeding for chordates: active predation

  • Craniates share some characteristics: a skull, brain, eyes, and other sensory organs

  • Craniates have two clusters of Hox genes; lancelets and tunicates have only one cluster

  • One feature unique to craniates is the neural crest, a collection of cells near the dorsal margins of the closing neural tube in an embryo

  • Neural crest cells give rise to a variety of structures, including some of the bones and cartilage of the skull

  • http://www.youtube.com/watch?v=00xr4kzYZn4 (neural tube formation)


Fig. 34-7 hollow nerve cord

Neural

crest

Neural

tube

Dorsal edges

of neural plate

Migrating neural

crest cells

Notochord


Hagfishes
Hagfishes hollow nerve cord

  • The least derived surviving craniate lineage is Myxini, the hagfishes

  • Hagfishes have a cartilaginous skull and axial rod of cartilage derived from the notochord, but lack jaws and vertebrae

Slime glands


Concept 34 3 vertebrates are craniates that have a backbone
Concept 34.3: Vertebrates are craniates that have a backbone hollow nerve cord

  • During the Cambrian period, a lineage of craniates evolved into vertebrates

  • Vertebrates became more efficient at capturing food and avoiding being eaten

  • Vertebrates underwent a second gene duplication involving the Dlx family of transcription factors

  • Vertebrates have the following derived characters:

    • Vertebrae enclosing a spinal cord

    • An elaborate skull

    • Fin rays, in the aquatic forms


Fig. 34-10 hollow nerve cord

  • Lampreys (Petromyzontida) represent the oldest living lineage of vertebrates

  • They are jawless vertebrates inhabiting various marine and freshwater habitats

  • They have cartilaginous segments surrounding the notochord and arching partly over the nerve cord


Concept 34 4 gnathostomes are vertebrates that have jaws
Concept 34.4: Gnathostomes are vertebrates that have jaws hollow nerve cord

  • Today, jawed vertebrates, or gnathostomes, outnumber jawless vertebrates

  • Gnathostomes have jaws that might have evolved from skeletal supports of the pharyngeal slits

  • Other characters common to gnathostomes:

    • An additional duplication of Hox genes

    • An enlarged forebrain associated with enhanced smell and vision

    • In aquatic gnathostomes, the lateral line system, which is sensitive to vibrations


Lateral line system
Lateral Line System hollow nerve cord


Concept 34 4 gnathostomes are vertebrates that have jaws1

Fig. 34-13-3 hollow nerve cord

Concept 34.4: Gnathostomes are vertebrates that have jaws

Gill slits

Cranium

Mouth

Skeletal rods

The skeleton of the jaws and their supports may have evolved from two pairs of skeletal rods (red and green) located between gills slits near the mouth. Pairs of rods anterior to those that formed the jaws were either lost or incorporated into the cranium or jaws.


Chondrichthyans sharks rays and their relatives
Chondrichthyans (Sharks, Rays, and Their Relatives) hollow nerve cord

  • Chondrichthyans (Chondrichthyes) have a skeleton composed primarily of cartilage

  • The cartilaginous skeleton evolved secondarily from an ancestral mineralized skeleton

  • Swim in primative vertebrate fashion (sinious)

  • Gills open separately to environment

  • The largest and most diverse group of chondrichthyans includes the sharks, rays, and skates

  • http://www.metacafe.com/watch/336740/great_white_shark_video/ (great white shark eating a seal)


Fig. 34-15a hollow nerve cord

Pelvic fins

Pectoral fins

(a) Blacktip reef shark (Carcharhinus melanopterus)


  • Most sharks hollow nerve cord

    • Have a streamlined body and are swift swimmers

    • Are carnivores

    • Have a short digestive tract; a ridge called the spiral valveincreases the digestive surface area

    • Have acute senses

  • Shark eggs are fertilized internally but embryos can develop in different ways:

    • Oviparous: eggs hatch outside the mother’s body

    • Ovoviviparous: the embryo develops within the uterus and is nourished by the egg yolk

    • Viviparous: the embryo develops within the uterus and is nourished through a yolk sac placenta from the mother’s blood

  • The reproductive tract, excretory system, and digestive tract empty into a common cloaca


Fig. 34-15b hollow nerve cord

(b) Southern stingray (Dasyatis americana)


Fig. 34-15c hollow nerve cord

(c) Spotted ratfish (Hydrolagus colliei)


Ray finned fishes and lobe fins
Ray-Finned Fishes and Lobe-Fins hollow nerve cord

  • The vast majority of vertebrates belong to a clade of gnathostomes called Osteichthyes

  • Osteichthyes includes the bony fish and tetrapods

  • Nearly all living osteichthyans have a bony endoskeleton

  • Aquatic osteichthyans are the vertebrates we informally call fishes

  • Most fishes breathe by drawing water over gills protected by an operculum

  • Fishes control their buoyancy with an air sac known as a swim bladder


Fig. 34-16 hollow nerve cord

Swim

bladder

Dorsal fin

Adipose fin

(characteristic

of trout)

Caudal

fin

Spinal cord

Brain

Nostril

Anal fin

Cut edge

of operculum

Lateral

line

Liver

Gills

Anus

Gonad

Heart

Stomach

Urinary

bladder

Pelvic

fin

Kidney

Intestine


Ray finned fishes
Ray-Finned Fishes hollow nerve cord

  • Class Actinopterygii, the ray-finned fishes, includes nearly all the familiar aquatic osteichthyans

  • The fins, supported mainly by long, flexible rays, are modified for maneuvering, defense, and other functions

  • http://www.youtube.com/watch?v=cKP53sB0itI (clown fish and sea anemone)

  • http://www.youtube.com/watch?v=iaoLxR9FTwk&feature=related (seahorse giving birth)


Fig. 34-18 hollow nerve cord

  • The lobe-fins (Sarcopterygii) have muscular pelvic and pectoral fins which can be used to “walk” underwater across the substrate

  • Three lineages survive and include coelacanths, lungfishes, and tetrapods


Conceptual summary1
Conceptual Summary: hollow nerve cord

  • These two classes of jawed fish also have two pairs of lagteral fins which allow fishes to balance and maneuver and were important in the evolution of paired limbs


Concept 34 5 tetrapods are gnathostomes that have limbs
Concept 34.5: Tetrapods are gnathostomes that have limbs hollow nerve cord

  • One of the most significant events in vertebrate history was when the fins of some lobe-fins evolved into the limbs and feet of tetrapods

  • The transition to land depended on solving probloems such as dehydration, lack of buoyant support, fertilization

  • Tetrapods have some specific adaptations:

    • Four limbs, and feet with digits

    • Ears for detecting airborne sounds

  • In one lineage of lobe-fins, the fins became progressively more limb-like while the rest of the body retained adaptations for aquatic life

  • For example, Acanthostegalived in Greenland 365 million years ago


Fig. 34-19 hollow nerve cord

Bones

supporting

gills

Tetrapod

limb

skeleton


Amphibians frogs salamanders toads newts
Amphibians: Frogs, Salamanders, Toads, Newts hollow nerve cord

  • Amphibians (class Amphibia) are represented by about 6,150 species of organisms in three orders

  • Amphibian means “both ways of life,” referring to the metamorphosis of an aquatic larva into a terrestrial adult

  • Amphibians require water for external fertilization and external embryonic development

    • No amnion

    • Excretes ammonia (by product of the breakdown of proteins & nucleic acids

  • Thin skinned – gas exchange through skin

  • First vertebrate with true tongue


Fig. 34-21 hollow nerve cord

(a) Order Urodela

(b) Order Anura

(c) Order Apoda


Fig. 34-22 hollow nerve cord

(a) Tadpole

(b) During

metamorphosis

(c) Mating adults


This frog incubates her eggs in a pouch of skin, helping to protect the eggs

from predators. When the eggs hatch, the female deposits the tadpoles in

water where they begin life on their own.


Concept 34 6 amniotes are tetrapods that have a terrestrially adapted egg
Concept 34.6: Amniotes are tetrapods that have a terrestrially adapted egg

  • Amniotes are a group of tetrapods whose living members are the reptiles, including birds, and mammals

  • Amniotes are named for the major derived character of the clade, the amniotic egg, which contains membranes that protect the embryo

  • The extraembryonic membranes are the amnion, chorion, yolk sac, and allantois

  • Amniotes have other terrestrial adaptations, such as relatively impermeable skin and the ability to use the rib cage to ventilate the lungs


The amniotic egg
The amniotic egg: terrestrially adapted egg

  • The embryos of reptiles and mammals form four extraembryonic membranes which is an evolutionary adaptation that protects developing embryo from drying out.

    • Amnion – The amnion protects the embryo in a fluid-filled cavity that cushions against mechanical shock.

    • Allantios – The allantois is a disposal sac for certain metabolic wasted produced by the embryo. The membrane of the allantois also functions with chorion as a respiratory organ.

    • Chorion – The chorion and the membrane of the allantois exchange gasses between the embryo and the air. Oxygen and carbon dioxide diffuse freely across the shell.

    • Yolk sac – The yolk sac contains the yolk, a stockpile of nutrients. Blood vessels in the yolk sac membrane transport nutrients from the yolk into the embryo. Other nutrients are stored in the albumen (“egg white”).


Fig. 34-25 terrestrially adapted egg

Chorion

Allantois

Yolk sac

Amnion

Embryo

Amniotic

cavity

with

amniotic

fluid

Yolk

(nutrients)

Albumen

Shell


Reptiles lizards snakes turtles and crocodiles
Reptiles: Lizards, Snakes, Turtles and Crocodiles terrestrially adapted egg

  • The reptile clade includes the tuataras, lizards, snakes, turtles, crocodilians, birds, and the extinct dinosaurs

  • They produce live born offspring or amniotic eggs which have membranes specialized for respiration, protection and storage of waste products. Fertilization is internal, embryonic development is external

  • Reptiles have scales that protect and reduce water loss

  • They lay shelled eggs on land

  • Ectothermic – taking most of their heat from the environment

  • Early reptiles showed much more diversity in methods of locomotion, feeding habits and life histories compared with modern reptiles.


Fig. 34-26 terrestrially adapted egg


Fig. 34-27 terrestrially adapted egg

(a) Tuatara (Sphenodon punctatus)

(b) Australian thorny devil

lizard (Moloch horridus)

(c) Wagler’s pit viper

(Tropidolaemus wagleri)

(d)Eastern box turtle (Terrapenecarolinacarolina)

(e) American alligator

(Alligator mississippiensis)



Birds
Birdshttp://www.arkive.org/galapagos-marine-iguana/amblyrhynchus-cristatus/video-06c.html

  • Birds are archosaurs, but almost every feature of their reptilian anatomy has undergone modification in their adaptation to flight

  • The major adaptation is wings with keratin feathers which provide protection, insulation, allow for flight and play a role in courtship rituals

    • Flight enhances hunting and scavenging, escape from terrestrial predators, and migration

    • Flight requires a great expenditure of energy, acute vision, and fine muscle control

  • Endothermic – generate heat by their metabolism

  • Other adaptations include lack of a urinary bladder, females with only one ovary, small gonads, and loss of teeth


Fig. 34-28http://www.arkive.org/galapagos-marine-iguana/amblyrhynchus-cristatus/video-06c.html

Finger 1

(b) Bone structure

Palm

(a) Wing

Finger 2

Finger 3

Forearm

Wrist

Shaft

Shaft

Barb

Vane

Barbule

Hook

(c) Feather structure


Fig. 34-29http://www.arkive.org/galapagos-marine-iguana/amblyrhynchus-cristatus/video-06c.html

Toothed beak

Wing claw

Fossil evidence indicates that

Archaeopteryx was capable

of powered flight but retained

many characters of nonbird dinasaurs.

Airfoil wing

with contour

feathers

Long tail with

many vertebrae


Fig. 34-30ahttp://www.arkive.org/galapagos-marine-iguana/amblyrhynchus-cristatus/video-06c.html

(a) Emu – a flightless bird


Fig. 34-30bhttp://www.arkive.org/galapagos-marine-iguana/amblyrhynchus-cristatus/video-06c.html

(b) Mallards – Like many birds the mallard exhibits pronounced color differences between the sexes


Fig. 34-30chttp://www.arkive.org/galapagos-marine-iguana/amblyrhynchus-cristatus/video-06c.html

(c) Laysan albatrosses – Most birds have specific , mating behaviors, such as this courtship ritual.


Fig. 34-30dhttp://www.arkive.org/galapagos-marine-iguana/amblyrhynchus-cristatus/video-06c.html

(d) Barn swallows – toes on their feet can lock around a branch or wire, enabling them to rest in place for long periods of time


Conceptual summary2
Conceptual Summaryhttp://www.arkive.org/galapagos-marine-iguana/amblyrhynchus-cristatus/video-06c.html

  • Feathers permit birds to fly while retaining other means of locomotion. They also contribute to endothermy, which has permitted birds to colonize most parts of the world.


Concept 34 7 mammals are amniotes that have hair and produce milk
Concept 34.7: Mammals are amniotes that have hair and produce milk

  • Mammalian evolutionary success is attributed to their:

    • Quadrapedal locomotion

    • Endothermy

    • Viviparity – live bearing (internal fertilization and development)

      • Integument (skin) and its derivatives (control body temp.)

  • Mammals have

    • Mammary glands, which produce milk

    • Hair

    • A larger brain than other vertebrates of equivalent size

    • Differentiated teeth


Monotremes
Monotremes produce milk

  • Monotremes are a small group of egg-laying mammals consisting of echidnas and the platypus


Fig. 34-32 produce milk


Marsupials
Marsupials produce milk

  • Marsupials include opossums, kangaroos, and koalas

  • The embryo develops within a placenta in the mother’s uterus

  • A marsupial is born very early in its development

  • It completes its embryonic development while nursing in a maternal pouch called a marsupium

(a) A young brushtail possum

(b) Long-nosed bandicoot



Fig. 34-34 diversity of marsupials that resemble the eutherians in other parts of the world

Marsupial

mammals

Marsupial

mammals

Eutherian

mammals

Eutherian

mammals

Plantigale

Deer mouse

Wombat

Woodchuck

Marsupial mole

Mole

Wolverine

Tasmanian devil

Sugar glider

Flying squirrel

Patagonian cavy

Kangaroo

  • In Australia, convergent evolution has resulted in a diversity of marsupials that resemble the eutherians in other parts of the world


Eutherians placental mammals
Eutherians (Placental Mammals) diversity of marsupials that resemble the eutherians in other parts of the world

  • Compared with marsupials, eutherians have a longer period of pregnancy

  • Young eutherians complete their embryonic development within a uterus, joined to the mother by the placenta

  • Placenta evolved from chorion and allantois and is formed from maternal and embryonic tissue

  • Molecular and morphological data give conflicting dates on the diversification of eutherians


Primates
Primates diversity of marsupials that resemble the eutherians in other parts of the world

  • The mammalian order Primates includes lemurs, tarsiers, monkeys, and apes

  • Humans are members of the ape group

  • Most primates have hands and feet adapted for grasping

  • Other derived characters of primates:

    • A large brain and short jaws

    • Forward-looking eyes close together on the face, providing depth perception

    • Complex social behavior and parental care

    • A fully opposable thumb (in monkeys and apes)


Fig. 34-36 diversity of marsupials that resemble the eutherians in other parts of the world


Fig. 34-39 diversity of marsupials that resemble the eutherians in other parts of the world

(a) Gibbon

(b) Orangutan

(c) Gorilla

(d) Chimpanzees

(e) Bonobos


Fig. 34-UN10a diversity of marsupials that resemble the eutherians in other parts of the world


Fig. 34-UN10b diversity of marsupials that resemble the eutherians in other parts of the world


Fig. 34-UN10c diversity of marsupials that resemble the eutherians in other parts of the world


Fig. 34-UN10d diversity of marsupials that resemble the eutherians in other parts of the world


Fig. 34-UN10e diversity of marsupials that resemble the eutherians in other parts of the world


Fig. 34-UN10f diversity of marsupials that resemble the eutherians in other parts of the world


Fig. 34-UN10g diversity of marsupials that resemble the eutherians in other parts of the world


Fig. 34-T1 diversity of marsupials that resemble the eutherians in other parts of the world


Fig. 34-UN11 diversity of marsupials that resemble the eutherians in other parts of the world


Fig. 34-UN12 diversity of marsupials that resemble the eutherians in other parts of the world


You should now be able to
You should now be able to: diversity of marsupials that resemble the eutherians in other parts of the world

  • List the derived traits for: chordates, craniates, vertebrates, gnathostomes, tetrapods, amniotes, birds, mammals, primates

  • Describe and distinguish between Chondrichthyes and Osteichthyes, noting the main traits of each group

  • Define and distinguish among amphibian, reptiles, and birds

  • Describe an amniotic egg and explain its significance in the evolution of reptiles and mammals

  • Explain why the reptile clade includes birds

  • Distinguish among monotreme, marsupial, and eutherian mammals


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