Evolution Biol 4802

Lecture 6

 

Topics for today

The fossil record

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

EvoBeaker: Dogs

 

Difficult to comprehend the age of the earth

  • Big bang ~14 byo
  • Earth ~4.6 byo
  • Oldest rocks ~3.8 byo
  • 1st living things ~3.5 byo
  • 1st animal life ~0.8 byo

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 doesn’t 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

Idea of a relative chronological sequence is not recent

  • Mid-1600’s 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

Timing of events needed to be defined

Calculation of earth’s age based on rate of:

Ideas that didn’t 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

 

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:
      • solidified
      • escape erosion, metamorphosis, subduction for millions of years
      • exposed

Three interpretations of patterns of change in the fossil record

  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

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

 

Changes in trilobite rib number over time

            What model best fits this data?

 

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

 

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

ü      Homology

ü      Change in form and function

ü      Mosaic evolution

2007 Lobe-finned fish Coelacanths

2007 Rare full-body imprint, skin texture

Example of dinosaurs to Birds (we skipped this example but will return to it later)

What model best fits this data

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

ü      Homology

ü      Change in form and function

ü      Mosaic evolution

ü      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

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

ü      Homology

ü      Change in form and function

ü      Mosaic evolution

  • Molecular phylogeny

ü      Cetacea whales, dolphins, seals

  • Intermediate forms

ü      Hippo-like ancestor

ü      Lived in shallow water used legs to swim

ü      Swam primarily with hind legs; couldn’t support itself on land

ü      Fully aquatic with nonfunctional pelvis and hindlimb

ü      Complete loss of hindlimb

 

Assignment 3

A single group submission is encouraged

Question 59 (page 14)

*     Describe the pattern of colonization your imposed (a few sentences)

*     Include the picture of your tree

*     Discuss the extent to which the pattern of colonization you imposed matches your tree (a few sentences)

 

Exercise 6 (pages 18-19)

*     Based on the figure on page 18, Write one paragraph that describes whether you think domesticated dogs came from different wolf lineages or the same one. Please refer to specific examples from the tree

*     Answer the question on page 19 in one paragraph.

 

Exercise 5  (pages 15-17)

*     Optional. I will give you 5 extra credit points (out of 100) for Mid-term Exam 1 only if it is completed when the workbooks are submitted