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Vertebrates. Chapter 34. 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. Principle Chordate Features. The Nonvertebrate Chordates.

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Chapter 34

the chordates
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
the nonvertebrate chordates
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
the nonvertebrate chordates6
The Nonvertebrate Chordates
  • Lancelets
    • scaleless, fishlike marine chordates
      • notochord runs entire length of dorsal nerve cord
      • feed on microscopic plankton using cilia-generated current
characteristics of vertebrates
Characteristics of Vertebrates
  • Vertebral column
  • Distinct, well-differentiated head
  • Neural crest
  • Internal organs
  • Endoskeleton
overview of the evolution of vertebrates
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
overview of the evolution of vertebrates9
Overview of the Evolution of Vertebrates
  • Four classes are land-dwelling tetrapods
    • Amphibia - amphibians
    • Reptilia - reptiles
    • Aves - birds
    • Mammalia - mammals
  • Over half of all vertebrates are fishes.
  • Characteristics
    • vertebral column
    • jaws and paired appendages
    • gills
    • single-loop blood circulation
    • nutritional deficiencies
history of the fishes
History of the Fishes
  • First fishes
    • members of five Ostracoderm orders
      • jawless bottom-dwellers
  • Evolution of the jaw
    • jaws developed about 410 mya
history of the fishes13
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
history of the fishes14
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
history of the fishes15
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
history of the fishes16
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
history of the fishes17
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
  • First vertebrates to walk on land
  • Characteristics
    • legs
    • cutaneous respiration
    • lungs
    • pulmonary veins
    • partially divided heart
history of the amphibians
History of the Amphibians
  • Adaptations for the invasion of land
    • legs to support body’s 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
history of the amphibians21
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
history of the amphibians22
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
history of the amphibians23
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
history of the amphibians24
History of the Amphibians
  • Urodela (Caudata) - salamanders
    • have elongated bodies, long tails, and sooth, moist skin
      • fertilization is usually external
history of the amphibians25
History of the Amphibians
  • Apoda (Gymnophiona)
    • caecilians - highly specialized group of tropical burrowing amphibians
      • legless, but have jaws and teeth
      • internal fertilization
  • Characteristics
    • amniotic egg
      • chorion - outermost membrane
      • amnion - encases embryo
      • yolk sac - surrounds yolk (food)
      • allantois - surrounds waste cavity
    • dry skin
    • thoracic breathing
rise and fall of dominant reptiles
Rise and Fall of Dominant Reptiles
  • Pelycosaurs: a better predator
    • first land vertebrates to kill organisms their own size
rise and fall of dominant reptiles28
Rise and Fall of Dominant Reptiles
  • Therapsids: speeding up metabolism
    • extremely high food consumption
      • endotherms?
rise and fall of dominant reptiles29
Rise and Fall of Dominant Reptiles
  • Thecodonts: wasting less energy
    • warmer climates - ectothermic
    • first bipedal land vertebrates
rise and fall of dominant reptiles30
Rise and Fall of Dominant Reptiles
  • Dinosaurs: learning to run
    • body located directly over legs
      • increased speed and agility
today s reptiles
Today’s Reptiles
  • Of the 16 orders of reptiles that have existed, only 4 survive
    • turtles
    • lizards and snakes
    • tuataras
    • crocodiles
rise and fall of dominant reptiles33
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
living reptiles
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
rise and fall of dominant reptiles35
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
rise and fall of dominant reptiles36
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
rise and fall of dominant reptiles37
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)
  • Class Aves contains 28 orders containing 166 families and about 8,600 species.
    • key characteristics
      • feathers
        • modified reptilian scales
      • flight skeleton
        • thin, hollow bones
history of the birds
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
history of the birds40
History of the Birds
  • Birds today
    • adaptations for flight energy demands
      • efficient respiration
      • efficient circulation
      • endothermy
  • Key mammalian characteristics
    • hair
      • heat loss
      • camouflage
      • sensory structures
      • defense weapon
    • mammary glands
      • about 50% of energy in milk comes from fat
key mammalian characteristics
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
key mammalian characteristics43
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
key mammalian characteristics44
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
orders of mammals
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
history of the mammals
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
evolution among primates
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”
  • 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