Vertebrates

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Vertebrates

• Chapter 35

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The Chordates

• Chordates (phylum Chordata) are deuterostome
  coelomates
• Closest relatives are echinoderms (the only other
  deuterostomes)
• Four features all chordates share
• 1. Nerve cord
• 2. Notochord
• 3. Pharyngeal slits
• 4. Postanal tail

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The Chordates

• All chordates have all four of these
  characteristics at some time in their lives
• Other characteristics also distinguish chordates
• 1. Chordate muscles are arranged in segmented
  blocks called somites
• 2. Most chordates have an internal skeleton
  against which the muscles work

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The Nonvertebrate Chordates

• Phylum chordata can be divided into three
  subphyla
• 1. Urochordata
• 2. Cephalochordata
• 3. Vertebrata

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Subphylum Urochordata

• Tunicates are marine animals
• Larvae are tadpolelike and have notochord and
  nerve cord
• Are free-swimming but do not feed
• Adults typically lose the tail and notochord
• Are immobile filter-feeders
• Many secrete a tunic (cellulose sac) that
  surrounds the animal

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Subphylum Urochordata
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Subphylum Cephalochordata

• Lancelets are scaleless chordates
• -Notochord persists throughout animals life
• -Have no distinguishable head

-Feed on plankton using cilia-generated currents
-Closest relatives to vertebrates
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Subphylum Vertebrata

• Vertebrates chordates with a spinal column
• Distinguished from nonvertebrates by
• 1. Vertebral column Encloses and protects
  the dorsal nerve cord
• 2. Head Distinct where sensory are organs
  are located

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Subphylum Vertebrata

• Vertebrates also have
• Neural crest A unique group of embryonic cells
  that forms many vertebrate structures
• Internal organs Liver, kidneys, endocrine
  glands, heart and closed circulatory system
• Endoskeleton Made of cartilage or bone
• Makes possible great size and extraordinary
  movement

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Fishes

• Fishes are the most diverse vertebrate group
• -Over half of all vertebrates

-Vary greatly in size, shape, color and
appearance
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Fishes

• Fishes have the following characteristics
• 1. Vertebral column
• 2. Jaws and paired appendages
• 3. Internal gills
• 4. Single-loop blood circulation
• 5. Nutritional deficiencies

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History of the Fishes

• In the Carboniferous period (360-280 MYA), sharks
  (Class Chondrichthyes) became the dominant sea
  predators
• A light, flexible skeleton, and paired fins made
  them superior swimmers

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History of the Fishes

• Sharks were among the first vertebrates to
  develop teeth
• Evolved from rough scales on mouths skin
• Easily lost but continuously replaced (works as a
  conveyer belt)
• Sharks (and bony fishes) have a fully developed
  lateral line system
• Series of sensory organs under the skin that
  detects changes in pressure waves

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History of the Fishes

• Reproduction in sharks differs from that of other
  fishes
• Shark eggs are fertilized internally, and pups
  are born alive
• A few species do lay fertilized eggs
• Parthenogenic sharks
• Sharks have long gestation periods and relatively
  few offspring
• Therefore, are not able to recover quickly from
  population declines
• Shark numbers are declining drastically worldwide
  (shark fin soup)

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History of the Fishes

• Bony fishes- Class Osteichthyes evolved at the
  same time as sharks about 400 MYA
• However, they adopted a heavy internal skeleton
  made completely of bone
• Bony fishes are the most species rich group of
  all vertebrates (gt 30,000 living species)
• They developed significant adaptations that
  enabled them to dominate life in the water
• Swim bladder and gill cover

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History of the Fishes

• Swim bladder
• A gas-filled sac that allows bony fishes to
  regulate their buoyant density
• Gas addition Gas gland
• Gas release Oval body
• Gill cover
• A hard plate, the operculum, covers gills
• Its flexing permits water pumping over gills

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History of the Fishes
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Amphibians

• Amphibians (class Amphibia) are damp-skinned
  vertebrates
• First vertebrates to walk on land
• Amphibians have several key characteristics
• 1. Legs
• 2. Lungs
• 3. Cutaneous respiration
• 4. Pulmonary veins
• 5. Partially divided heart

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History of Amphibians

• Successful invasion of lands by vertebrates
  required several adaptations
• 1. Legs to support bodys weight
• 2. Lungs to extract oxygen from air
• 3. Redesigned heart to drive larger muscles
• 4. Reproduction in H2O to prevent egg drying
• 5. System to prevent whole body desiccation

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Modern Amphibians

• Today there are about 5,670 species in 37
  different families, comprising three orders
• Anura (without tail)
• Caudata (visible tail)
• Apoda (without legs)

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Modern Amphibians

• Order Anura (frogs and toads)
• Frogs have smooth, moist skin and long legs
• Most live in or near water
• Toads have bumpy, dry skin and short legs
• Most live in dry environments
• Eggs are fertilized externally
• Hatched into swimming tadpole larvae
• Undergo metamorphosis into adults

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Modern Amphibians

• Order Caudata (salamanders)
• Have long bodies, tails smooth, moist skin
• Live in moist places
• Eggs are fertilized internally
• Larvae similar to adults
• Order Apoda (caecilians)
• Tropical, burrowing amphibians
• Legless with small eyes and jaws with teeth
• Fertilization is internal

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Modern Amphibians
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Reptiles

• Over 7000 species of reptiles (class Reptilia)
  now live on Earth
• All living reptiles exhibit three key features
• 1. Amniotic eggs, which are watertight
• 2. Dry skin, which covers body and prevents
  water loss
• 3. Thoracic breathing, which increases lung
  capacity

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Reptiles

• Reptiles, birds and mammals are amniotes
• The amniotic egg has four membranes
• Chorion Allows O2 entry
• Amnion Fluid-filled cavity
• Yolk sac Provides food
• Allantois Excretes wastes

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Reptiles
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History of Reptiles

• Reptiles dominated earth for 250 million years
• Reptiles are distinguished by the number of holes
  on side of the skull behind eye orbit
• 0 (anapsids), 1 (synapsids), 2 (diapsids)

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Modern Reptiles

• Modern reptiles developed two important
  characteristics
• 1. Internal fertilization Sperm fertilizes egg
  before protective membranes are formed
• 2. Improved circulation Oxygen is provided to
  the body more efficiently

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Modern Reptiles

• All living reptiles are ectothermic
• Obtain heat from external sources
• There are four surviving orders of reptiles
• Chelonia (turtles and tortoises)
• Rhynchocephalia (tuataras)
• Squamata (lizards and snakes)
• Crocodylia (crocodiles and alligators)

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Order Chelonia

• Whats the difference between turtles and
  tortoises?
• Tortoises are terrestrial
• Have dome-shaped shell
• Turtles are mostly aquatic
• Have disc-shaped shells

• Both lack teeth but have sharp beaks
• Marine turtles must return to land to lay eggs

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Order Rhynchocephalia

• Contains only two species of tuataras
• -Large, lizardlike animals about half a meter
  long

-Only found on islands near New Zealand

• Feature a parietal eye
• Inconspicuous third eye on top of head

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Order Squamata

• Contains about 3800 species of lizards and about
  3000 species of snakes
• A characteristic of this order is the presence of
  paired copulatory organs in the male

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Order Squamata

• Most lizards and snakes are carnivores
• Only two species of lizards are venomous
• Gila monster and beaded lizard
• Four of the 13 snake families contain venomous
  species
• Elapids, sea snakes, vipers and colubrids

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Order Crocodylia

• Composed of 25 species of large, primarily
  aquatic carnivorous reptiles
• Crocodiles live near or in water in tropical and
  subtropical regions
• Are typically nocturnal
• Alligators exist in only two species
• One in Southern US other in China
• Caimans are native to Central America
• Gharials live only in India and Burma

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Order Crocodylia
Crocodile
Gharial

• In many ways, crocodiles resemble birds far more
  than they do other living reptiles
• Build nests and care for their young
• Have a four-chambered heart

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Birds

• Birds (class Aves) are the most diverse of all
  terrestrial vertebrates
• -28 orders, 166 families, about 8600 species

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Birds

• Birds still retain many reptilian traits
• Amniotic eggs and scales on legs
• Two major traits distinguish then, however
• 1. Feathers
• Provide lift for flight and conserve heat
• 2. Flight skeleton
• Bones are thin and hollow
• Many are fused (collarbone and keeled breastbone)

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History of Birds

• Most paleontologists agree that birds are the
  direct descendants of theropod dinosaurs
• Archaeopteryx is the first known bird

-Had skull with teeth -Feathers on wings and
tail
-Forelimbs nearly identical to those of theropods
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History of Birds

• The most ancient living birds appear to be the
  flightless birds, such as ostrichs
• The largest of the bird orders, Passeriformes,
  appears to have evolved the latest
• Many adaptations enabled birds to cope with the
  heavy energy demands of flight

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History of Birds

• 1. Efficient respiration
• -Air passes all the way through lungs in a
  single direction
• 2. Efficient circulation
• -Muscles receive fully oxygenated blood
• -Rapid heartbeat
• 3. Endothermy
• -Body temperature (40-42oC) permits higher
  metabolic rate

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Mammals

• There are about 4500 species of mammals (class
  Mammalia)
• -Lowest number among 5 vertebrate classes
• Mammals differ from other vertebrates in two
  fundamental traits
• 1. Hair
• -Long, keratin-rich filaments that extend from
  hair follicles
• -Insulation, camouflage, sensory structure
• 2. Mammary glands
• -Females possess mammary glands that secrete
  milk

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Mammals

• Other notable features of mammals include
• Endothermy
• Depends on more efficient
• Circulation Four-chambered heart
• Respiration Diaphragm
• -Placenta
• Specialized organ that brings fetal and maternal
  blood into close contact

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Mammals
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Mammals

• The mammalian lineage also gave rise to several
  adaptations in some groups
• 1. Specialized teeth
• -Different types of teeth are highly
  specialized to match particular eating habits

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Mammals

• 2. Digestion of plants
• -Herbivorous mammals rely on mutualistic
  partnerships with bacteria for cellulose
  breakdown
• 3. Development of hooves and horns
• -Hooves are specialized keratin pads
• -Horns are bone surrounded by keratin
• -Antlers are made of bone, not keratin

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Mammals

• 4. Flying mammals Bats
• -Bat wing is a leathery membrane of skin and
  muscle stretched over 4 finger bones

-Bats navigate in the dark by echolocation
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The Two Subclasses of Mammals

• Prototheria (most primitive)
• Lay shelled eggs
• One living group
• Monotremes
• Theria
• Viviparous Young are born alive
• Two living groups
• Marsupials and placental mammals

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Monotremes Egg-laying Mammals

• Only three living monotremes
• -Duck-billed platypus

-Short-nosed echidna
-Long-nosed echidna
-Have single opening, cloaca for digestive and
reproductive tracts
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Marsupials Pouched Mammals

• Egg has chorion and amnion, but no shell
• Embryo is nourished by abundant yolk
• -After birth, it crawls into marsupial pouch
• -Latches onto nipple continues to develop
• Examples
• -Kangaroo
• -Opossum

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Placental Mammals

• Produce a true placenta that nourishes embryo
  throughout its development
• Forms from both fetal and maternal tissue
• Includes most
• living mammals