Vertebrates

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Chapter 34

• Vertebrates

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Four anatomical features of Chordata

• Notochord
• Longitudinal flexible rod located between the
  digestive tube and the nerve cord
• Provides skeletal support
• Dorsal, hollow nerve cord
• Pharyngeal slits
• Muscular, postanal tail

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Invertebrate Chordates

• Provide clues to the origin of vertebrates
• Subphylum Urochordata
• Tunicates
• Subphylum Cephalochordata
• Lancelets

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Vertebrates

• Neural crest forms above the growing nerve cord
  and forms bones of cranium and other anatomy
• This separates vertebrate chordates from other
  chordate
• High degree of cephalization

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Vertebrates

• Hagfish do not have a vertebral column but are
  included in the survey of vertebrates because of
  a cranium
• Fast moving lifestyle
• Axial skeleton
• Faster digestion
• Growing skeleton

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Jawless Vertebrates

• Agnathans without jaws
• Includes the hagfish and lampreys
• Class Myxini hagfish
• Most primitive living vertebrates
• Secrete a slime as defense

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Jawless Vertebrates

• Class Cephalaspidomorphi lampreys
• Contains a true vertebral column
• Lack paired appendages (like hagfish)

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Fishes and Amphibians

• Gnathostomes jawed fishes
• Two extant classes Chondrichthyes and Osteichtyes
• Fishes also have paired appendages

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Evolution of Jaw
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Class Chondrichthyes

• Sharks, and rays
• Name means cartilaginous fish
• Cartilage for skeleton is a derived
  characteristic not a primitive one
• Whats the difference?

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Osteichthyes

• Most numerous vertebrates
• Bony fishes
• Once a single class now divided into three extant
  classes
• Class Actinopterygii ray finned fish
• Trout, bass
• Class Actinistia lobe finned fish
• Coelocanth
• Class Dipnoi lungfish
• Live in shallow waters and gulp air into a
  primitive lung

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Tetrapod evolution
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Class Amphibia

• Salamanders, frogs, and caecilians
• Require water for reproduction
• Probably evolved from a lungfish
• Rely heavily on moist skin for gas exchange

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Amniotes

• Noted by the evolution of the amniotic egg
• Evolved major adaptations for life on land

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Reptilian Characteristics

• Scaly skin for the prevention of dessication
• Advanced lungs
• Lay shelled eggs
• Cold blooded

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Class Aves

• Evolved during the great reptilian radiation of
  the Mesozoic era
• Anatomy is modified to aid in flight
• Endothermic warm blooded
• Brains are considerably larger than reptiles

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Class Mammalia

• Evolved rapidly with the extinction of the
  dinosaurs
• Posses mammary glands
• Hair
• Warm blooded
• Give live birth
• Evolved from a reptile ancestor

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Mammal and Reptile
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Class Mammalia

• Monotremes platypuses, and echidnas
• Still lay eggs
• Marsupials opossums, kangaroos
• Young born very early and continue development in
  a specialized pouch
• Most live in Australia
• Eutherian placental mammals
• Longer period of pregnancy

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Primates and Evolution of Homo sapiens

• Order Primates includes humans
• Most have hands and feet for grasping
• Large brains and short jaws
• Forward looking eyes
• Opposable thumbs
• Most are tree dweller
• Humans still maintain anatomy for tree living
  life

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Modern Primates
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Origins of Humans

• We did not come from chimpanzees
• We do share a common ancestor with chimpanzees
• At times several different human species lived
  together

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Adaptations

• Grasping fingers for tree life
• Binocular vision
• jumping from branch to branch requires good depth
  perception
• Large Brains
• brains size compared to body size is greatest in
  primates

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Hominids

• 20-30 mya dryopithecines developed from tree
  dwelling primates
• dryopithecines were ancestors to hominids (humans
  and fossil relatives) and pongids (great apes)
• 5-8 mya hominid line diverged from the pongid line

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Australopithecus

• Large brain human ancestor
• knees straightened out allowing for bipedal
  locomotion
• Genus Homo diverged from genus Australopithecus
  2.5 mya
• Homo species had more human like limb proportions

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Homo ergaster

• Gave rise to H. erectus, as well as H.
  heidelbergensis
• erectus first hominid to leave Africa
• average brain size was that of a small adult
• brow ridge, and no chin
• heidelbergensis migrated to Europe
• gave rise to Neanderthals
• meanwhile back in Africa gave rise to H. sapiens

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Neanderthals

• Large brained organims
• first appeared 150,000 ya
• 70,000 ya spread throughout Europe
• 30,000 ya were extinct

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Modern Humans

• arose 150,000 ya
• early human fossils known as Cro-Magnons
• Fossil records date back to 90,000 ya
• with smooth dome, prominent chins
• Created art in caves
• H. sapiens and H. neanderthalensis coexisted in
  same region during same time

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