Evolution Biol 4802

Lecture 6, Chapter 4

 

Topics for today

The fossil record

  1. Radiometric dating
  2. How to interpret gaps?
  3. Intermediate forms

 

If we can show cladogenesis with extant taxa, why do we need to consider the fossil record anymore?

  • Evidence of extinct species
  • Details of change that doesnt need to be inferred
  • Change in biodiversity over time
  • Massive extinctions
  • Great radiations
  • Movement with continental shifts
  • Calibration of molecular clocks
  • Information about past environments

Fig. 2.1 (new and old)

Idea of a relative chronological sequence is not recent

  • Mid-1600s recognized superposition
  • Lower strata and the fossils they contain are older than the strata and fossils above them

Geological Sequence

  • Order of eras, periods, epochs was agreed upon before good dating methods were available
  • Boundaries most often marked by changes in composition of fossils

Table 4.1 (new and old)

Timing of events needed to be defined

Calculation of earths age based on rate of:

Ideas that didnt work

        Cooling of the earth

        Sedimentary build up of rock

        Increase in salinity in the oceans

Radioactive material decays at a constant rate

Radioactive clocks tick at different rates

Fig. 4.2 (new and old)

The fossil record is extremely incomplete

        How many are there?

    • 250,000 fossil species described
    • << 1% of organisms that lived in the past

        Why so few?

    • Delicate bodies
    • Environment promotes rapid decay
    • Sediments form episodically
    • Conditions for fossilization are rare
      • Sediments must become:
        1. solidified
        2. escape erosion, metamorphosis, subduction for millions of years
        3. exposed

Three interpretations of patterns of change in the fossil record

Fig. 4.19 new (4.18 older version of the book)

  1. Phyletic gradualism

        Evolutionary change is incremental

        Not necessarily associated with speciation

  1. Punctuated equilibrium

        Evolutionary change associated with speciation

        Rapid change thereafter followed by stasis

  1. Punctuated gradualism

        Evolutionary change is rapid followed by stasis

        Speciation does not necessarily occur

How should the patterns differ if you are looking at changes within species?

Example of grassland vole teeth attributes

What model best fits this data?

        Grass wears down molars

        Favorable attributes:

o       Longer teeth

o       Enamel

o       Cement

Fig. 4.20 (4.19 old)

Exceptionally fine-scaled fossil record (Nevada) of stickleback fish

What model best fits this data?

        Open pit diatomite mine

        Strata laid down annually for 110,000 years

        Sampled layers 5,000 years apart

Fig. 4.4 (old and new)

Changes in trilobite rib number over time

What model best fits this data?

Fig. 4.21 (4.20 old)

How should the patterns differ if you are looking at changes higher taxonomic groups?

Fig. 4.6 (this figure only appears in the older version of the book so reproduced below))

Evolution-Fig-04-06-2

 

 

Example of lobe-finned fish and intermediates to amphibians

What model best fits this data?

  • Link between higher taxonomic levels
  • Origin of major body form, tetrapod vertebrate
  • Examples of

      Homology

      Change in form and function

      Mosaic evolution

2007 Lobe-finned fish Coelacanths

2007 Rare full-body imprint, skin texture

Example of dinosaurs to Birds

Fig. 4.7 (4.9 older version)

What model best fits this data

  • Link between higher taxonomic levels
  • Origin of major body form, flying vertebrate
  • Examples of

      Homology

      Change in form and function

      Mosaic evolution

      Preadaptation

         Expanded and fused brain case

         Reduction and fusion of digits

         Fusion of pelvic bones

         Reduced and fused tail vertebrate

         Big keeled sternum

         Strengthened rib cage

         Long hand bones

         Similar leg structure

2003 feathered dinosaur found in China 140 myo

Fig. 4.8 (old and new)

Example of hippos to whales

What model best fits this data?

  • Link between higher taxonomic levels
  • Origin of major body form, aquatic mammal
  • Examples of

      Homology

      Change in form and function

      Mosaic evolution

  • Molecular phylogeny

      Cetacea whales, dolphins, seals

  • Intermediate forms

      Hippo-like ancestor

      Lived in shallow water used legs to swim

      Swam primarily with hind legs; couldnt support itself on land

      Fully aquatic with nonfunctional pelvis and hindlimb

      Complete loss of hindlimb

Fig. 4.11 (old and new)