Vertebrates

1
Vertebrates

• Chapter 34

2
The Chordates

• Distinguished by four principle features some
  time in their lives
• nerve cord
• notochord
• pharyngeal slits
• postnatal tail
• Muscles arranged in segmented blocks
• Most have internal skeleton

3
Principle Chordate Features
4
The Nonvertebrate Chordates

• Tunicates
• exhibit neither a major body cavity nor visible
  segmentation
• tadpole larva clearly exhibit all basic
  characteristics of a chordate
• adults exist as sessile filter-feeders

5
Tunicates
6
The Nonvertebrate Chordates

• Lancelets
• scaleless, fishlike marine chordates
• notochord runs entire length of dorsal nerve cord
• feed on microscopic plankton using
  cilia-generated current

7
Characteristics of Vertebrates

• Vertebral column
• Distinct, well-differentiated head
• Neural crest
• Internal organs
• Endoskeleton

8
Overview of the Evolution of Vertebrates

• First vertebrates evolved in the oceans about 470
  mya.
• hinged-jaw
• amphibians on land
• reptiles take over
• split into birds and mammals

9
Overview of the Evolution of Vertebrates

• Four classes are land-dwelling tetrapods
• Amphibia - amphibians
• Reptilia - reptiles
• Aves - birds
• Mammalia - mammals

10
Fishes

• Over half of all vertebrates are fishes.
• Characteristics
• vertebral column
• jaws and paired appendages
• gills
• single-loop blood circulation
• nutritional deficiencies

11
Evolution of the Fishes
12
History of the Fishes

• First fishes
• members of five Ostracoderm orders
• jawless bottom-dwellers
• Evolution of the jaw
• jaws developed about 410 mya

13
History of the Fishes

• Rise of active swimmers
• Sharks and bony fishes replaced primitive fishes
  due to a superior swimming design.
• caudal (tail) fin
• dorsal (stabilizing) fins
• pectoral (shoulder - elevator) fins
• pelvic (hip- elevator) fins

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History of the Fishes

• Sharks become top predators
• sharks among first vertebrates to develop teeth
• sit on top of jaws
• programmed tooth loss
• teeth are always new and sharp
• extremely advanced reproduction
• shark eggs fertilized internally

15
History of the Fishes

• Bony fishes dominate the water
• bony fish evolved at same time as sharks, but
  adopted a heavy internal skeleton made of bone
• strong base for muscles
• evolved in fresh water
• highly mobile fins, thin scales, and completely
  symmetrical tails

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History of the Fishes

• Important adaptations of bony fishes
• swim bladder - regulates buoyancy
• lateral line system - assesses rate of movement
  through water as pressure waves against the
  lateral line
• gill cover (operculum) - flexing the operculum
  permits bony fish to pump water over their gills

17
History of the Fishes

• Path to land
• Lobe-finned fishes evolved 390 mya.
• have paired fins that consist of a long fleshy
  muscular lobe supported by a central core of
  bones that form fully articulated joints
• amphibians almost certainly evolved from
  lobe-finned fishes

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Lobe-Finned Fish and Primitive Amphibians
19
Amphibians

• First vertebrates to walk on land
• Characteristics
• legs
• cutaneous respiration
• lungs
• pulmonary veins
• partially divided heart

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History of the Amphibians

• Adaptations for the invasion of land
• legs to support bodys weight
• lung to extract oxygen from the air
• redesigned heart to drive new respiratory system
• reproduction in water to prevent egg desiccation
• system to prevent body desiccation

21
History of the Amphibians

• Rise and fall of amphibians
• became common during Carboniferous period 360-280
  mya
• began to leave marshes for dry uplands during
  early Permian period
• large size and complete body covering indicate
  skin was not used as respiratory system

22
History of the Amphibians

• By the end of Permian, therapsid (reptile)
  ousted amphibians from their niche on land
• by the end of the Triassic, there were only 15
  families of amphibians left
• almost all were aquatic
• only two groups are known from Jurassic period
  (213-144 mya)
• Anura - frogs and toads
• Urodela - salamanders and newts

23
History of the Amphibians

• Amphibians today
• Anura - amphibians without tails
• most live in or near water, and return to water
  to reproduce
• eggs fertilized externally and hatch into
  tadpoles
• metamorphosis

24
History of the Amphibians

• Urodela (Caudata) - salamanders
• have elongated bodies, long tails, and sooth,
  moist skin
• fertilization is usually external

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History of the Amphibians

• Apoda (Gymnophiona)
• caecilians - highly specialized group of tropical
  burrowing amphibians
• legless, but have jaws and teeth
• internal fertilization

26
Reptiles

• Characteristics
• amniotic egg
• chorion - outermost membrane
• amnion - encases embryo
• yolk sac - surrounds yolk (food)
• allantois - surrounds waste cavity
• dry skin
• thoracic breathing

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Rise and Fall of Dominant Reptiles

• Pelycosaurs a better predator
• first land vertebrates to kill organisms their
  own size

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Rise and Fall of Dominant Reptiles

• Therapsids speeding up metabolism
• extremely high food consumption
• endotherms?

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Rise and Fall of Dominant Reptiles

• Thecodonts wasting less energy
• warmer climates - ectothermic
• first bipedal land vertebrates

30
Rise and Fall of Dominant Reptiles

• Dinosaurs learning to run
• body located directly over legs
• increased speed and agility

31
Todays Reptiles

• Of the 16 orders of reptiles that have existed,
  only 4 survive
• turtles
• lizards and snakes
• tuataras
• crocodiles

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Evolutionary Relationships
33
Rise and Fall of Dominant Reptiles

• Other important characteristics
• internal fertilization
• improved circulatory system
• ectothermic - heat obtained from external sources
• endothermic - generate own heat
• homeothermic - constant body temperature
• poikilothermic - body temperature fluctuates with
  ambient temperature

34
Living Reptiles

• Order Chelonia turtles and tortoises
• differ from other reptiles because their bodies
  are encased within a protective shell
• anapsid - lack temporal opening in the skull,
  characteristic of other living reptiles

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Rise and Fall of Dominant Reptiles

• Order Rhynchocephalia tuatara
• lizardlike animals about half a meter long
• contain parietal eye
• only found on island off New Zealand coast

36
Rise and Fall of Dominant Reptiles

• Order Squamata lizards and snakes
• three suborders
• Sauria - lizards
• Amphisbaenia - worm lizards
• Serpentes - snakes
• paired copulatory organ in males
• lower jaw not joined directly to skull

37
Rise and Fall of Dominant Reptiles

• Order Crocodilia crocodiles and alligators
• remained relatively unchanged
• only two species of alligators
• southern US and China
• resemble birds more than other living reptiles
  (care for young and four-chambered heart)

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Birds

• Class Aves contains 28 orders containing 166
  families and about 8,600 species.
• key characteristics
• feathers
• modified reptilian scales
• flight skeleton
• thin, hollow bones

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History of the Birds

• Descended from dinosaurs
• Archaeopteryx
• Aves listed as separate class because of key
  evolutionary novelties of feathers, light bones,
  and super-efficient lungs

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History of the Birds

• Birds today
• adaptations for flight energy demands
• efficient respiration
• efficient circulation
• endothermy

41
Mammals

• Key mammalian characteristics
• hair
• heat loss
• camouflage
• sensory structures
• defense weapon
• mammary glands
• about 50 of energy in milk comes from fat

42
Key Mammalian Characteristics

• endothermy
• crucial adaptation that allowed activity at any
  time of the day to colonize severe environments
• placenta
• specialized organ allowing food, water, and
  oxygen to pass from mother to child
• teeth
• heterodont dentition

43
Key Mammalian Characteristics

• digestion of plants
• cellulose major source of food for herbivores
• mammals do not have necessary digestive enzymes
  to break apart cellulose
• some have evolved four-chambered stomachs
• some contain mutualistic bacteria in a cecum

44
Key Mammalian Characteristics

• hooves and horns
• hooves specialized pads of keratin
• horns composed of core of bone surrounded by
  keratin sheath
• flight
• bats have wing of leathery membrane of skin
  stretched over the bones of four fingers
• second largest order of mammals
• echolocation

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Orders of Mammals

• Origin of mammals
• first mammals arose about 220 mya
• tiny shrewlike creatures with large eye sockets -
  nocturnal?
• Early divergence
• Subclass Prototheria
• duckbill platypus
• Subclass Theria
• marsupials and placental mammals

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History of the Mammals

• Orders of mammals
• monotremes egg-laying mammals
• lay shelled eggs
• marsupials pouched mammals
• finish development in external pouch
• placental mammals
• placenta nourishes embryo throughout entire
  development

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Evolution Among Primates

• Primates
• two distinct features allowed them to succeed in
  arboreal environment
• grasping fingers and toes
• binocular vision
• Evolution of prosimians
• earliest primates split into prosimians and
  anthropoids about 40 mya
• before monkeys

48
Anthropoids

• Higher primates - includes apes, monkeys, and
  humans
• one of most contentious issues in primate biology
  is identity of first anthropoid
• Direct descendents
• New World monkeys
• Old World monkeys

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Primate Evolutionary Tree