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Week 5: Stages of Vertebrate Evolution

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Week 5: Stages of Vertebrate Evolution. Phylogenies: Trees of Life. Linnaeus: Linnaean System of Classification Based on similarity of traits Hierarchical: Kingdom Phylum Class Order Family Genius Species K ings P lay C hess O n F ine G rained S and

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phylogenies trees of life
Phylogenies: Trees of Life
  • Linnaeus: Linnaean System of Classification
  • Based on similarity of traits
  • Hierarchical:
    • Kingdom
    • Phylum
    • Class
    • Order
    • Family
    • Genius
    • Species

Kings Play Chess On Fine Grained Sand

Keep Pots Clean Or Family Get Sick


Humans are:

Kingdom: Animal

Phylum: Cordate (Sub Phylum Vertebrate)

Class: Mammal

Order: Primate

Family: Hominid (Super Family Hominoid)

Genius Homo

Species Sapiens

inheritance or convergence
Inheritance or Convergence?
  • Homologous = Similar because of common decent (share a recent common ancestor) – Inheritance.
  • Analogous = Similar because of adaptation to the same or similar environmentally stable problem (Bird and Bat wings) - Convergence.
phylogenies use homologous structures traits and must avoid analogous structures
Phylogenies use homologous structures (traits) and must avoid analogous structures







Derived Trait Analogous Trait Ancestral Trait

(last common ancestor) (convergence) (common ancestor of all 3)

systematics the study that distinguishes ancestral from derived traits
Systematics: the study that distinguishes ancestral from derived traits

Ancestral Traits

  • Appear earlier in embryonic development
    • Ontology recapitulates phylogeny
  • Appear earlier in the fossil record
    • Older traits
  • Seen in out-groups
    • If a trait is absence in one species but seen in other more distant lineages (tails)
  • Solid Notochord (no longer solid in humans)
    • Bilateral symmetry
    • Cephalization (head)
    • Tails
    • Endoskeleton
    • Three layer construction
      • Ectoderm
      • Mesoderm
      • Endoderm
  • Dorsal Nerve cord (spinal cord)
  • Brachial arches (gills in fish, seen in embryonic development in people)
  • Bony Vertebral Column (backbone)
  • Cranium (skull)
  • Three part brain
  • Olfactory organs (smell)
  • Eyes
  • Skin
  • Internal Organs
fish to amphibian to reptile
Fish to Amphibian to Reptile
  • Our Fish Heritage
    • Adaptive radiation associated with new niches created by higher levels of Oxygen in the environment (age of fish, Paleozoic 245 to 545 mya).
    • Backbones may have been an adaptation associated with swimming
    • Some early fish became larger and evolved skeletons, perhaps to avoid predation,
    • Evolved jaws to become predators
      • Earlier fish had larger throats to suck up water with food in it (like filter feeders today)
    • Evolved fins for stability in water
Our Amphibian Heritage
    • Some fresh water fish evolved fleshy lobed fins (2 front & 2 back) to support their bodies out of water
      • Adaptation to move from pond to pond
    • New theory is that lobed fins are adaptations to mangrove swamps which have lots of vegetation and roots to hide in but created difficulty for moving through, strong fleshy lobed fins allow for wiggling and pulling and pushing your way through this environment.
    • Air bladder evolve into lungs that allow early amphibians to live on land
      • Adaptation for avoiding predators
      • Opens up new niche (land plants and insects)
Amphibians retain:
    • Egg laying in water
    • Free swimming stage of development with gills and fins
  • Living on land (no buoyancy) selects for changes in skeletons
    • Thicker to support wait
    • Limbs for walking

Modern Amphibians stayed in early niche

    • Close to water
    • Insect eating
Our Reptilian Heritage
    • Age of Reptiles (Mesozoic Era, 245 to 264 mya)
    • Adaptive Radiation for new land niche
      • Adaptations include:
        • No longer need to return to water to lay eggs
        • Egg with amniotic structure (hard shell & yoke)
          • Development of nesting (nest guarding) behaviors
        • No swimming stage (babies look like adults)
        • Dry skin
        • Internal fertilization
          • Development of mating behaviors
Our Mammalian Heritage
    • Age of Mammals (Cenozoic, 70 mya)
    • Adaptive Radiation into what niche?
      • Maybe not special niche but vacated niche
      • Reproductive advantage
    • Mammalian Adaptations
      • Faster
        • Limbs moved under the body to get belly off the ground
      • Warm blooded (endothermic), better circulatory system (heart)
      • Hetrodontic (different teeth with different specializations
      • Live Birth
      • Lactation (parenting)
      • Hair
      • Good ears (inter ear)
      • Better Brain (we will elaborate much more on this later in the course)