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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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Vertebrates l.jpg

Vertebrates

Chapter 34


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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


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Principle Chordate Features


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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


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Tunicates


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The Nonvertebrate Chordates

  • Lancelets

    • scaleless, fishlike marine chordates

      • notochord runs entire length of dorsal nerve cord

      • feed on microscopic plankton using cilia-generated current


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Characteristics of Vertebrates

  • Vertebral column

  • Distinct, well-differentiated head

  • Neural crest

  • Internal organs

  • Endoskeleton


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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


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Overview of the Evolution of Vertebrates

  • Four classes are land-dwelling tetrapods

    • Amphibia - amphibians

    • Reptilia - reptiles

    • Aves - birds

    • Mammalia - mammals


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Fishes

  • Over half of all vertebrates are fishes.

  • Characteristics

    • vertebral column

    • jaws and paired appendages

    • gills

    • single-loop blood circulation

    • nutritional deficiencies


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Evolution of the Fishes


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History of the Fishes

  • First fishes

    • members of five Ostracoderm orders

      • jawless bottom-dwellers

  • Evolution of the jaw

    • jaws developed about 410 mya


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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


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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


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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


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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 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


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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


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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


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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


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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


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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


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Rise and Fall of Dominant Reptiles

  • Dinosaurs: learning to run

    • body located directly over legs

      • increased speed and agility


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Today’s 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


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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


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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


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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


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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


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Mammals

  • Key mammalian characteristics

    • hair

      • heat loss

      • camouflage

      • sensory structures

      • defense weapon

    • mammary glands

      • about 50% of energy in milk comes from fat


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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


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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


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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”


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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


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