Transcript Chapter 5: Stages of Vertebrate Evolution

Week 5: Stages of Vertebrate
Evolution
Phylogenies: Trees of Life
• Linnaeus: Linnaean System of Classification
• Based on similarity of traits
• Hierarchical:
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Kingdom
Phylum
Class
Order
Family
Genius
Species
Kings Play Chess On Fine Grained Sand
Keep Pots Clean Or Family Get Sick
Humans are:
Kingdom:
Phylum:
Class:
Order:
Family:
Genius
Species
Animal
Cordate (Sub Phylum Vertebrate)
Mammal
Primate
Hominid (Super Family Hominoid)
Homo
Sapiens
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
Present
Past
Yes
Derived Trait
(last common ancestor)
No
Analogous Trait
(convergence)
No
Ancestral Trait
(common ancestor of all 3)
Using Overall Similarity of Traits Leads to the Wrong Family Tree
Using Similarity of Derived Traits Leads to the Correct Family Tree
Using Similarity of Derived Traits Leads to the Correct Family Tree
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)
Cordates
• Solid Notochord (no longer solid in humans)
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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)
Vertebrates
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Bony Vertebral Column (backbone)
Cranium (skull)
Three part brain
Olfactory organs (smell)
Eyes
Skin
Internal Organs
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)