Fossils

Steven Dutch  University of Wisconsin - Green Bay  

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Fossils - Remains of Ancient Plants And Animals, Evidence of Life

Commonly Preserved
Hard Parts of Organisms:

• Bones
• Shells
• Hard Parts of Insects
• Woody
• Material

Rarely Preserved
Soft or Easily Decayed Parts of Organisms

• Internal Organs
• Skin
• Hair
• Feathers

Types of Fossils

• Original Material
• Casts & Molds
• Replacement (Petrified Wood)
• Carbonized Films (Leaves)
• Footprints, Tracks, Etc.

Pseudo Fossils: Look Like Fossils But Aren't

• Dendrites
• Concretions

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Fossils Occur Almost Exclusively in Sedimentary Rocks

• Heat of Melting or Metamorphism Would Destroy Almost Every Type of Fossil
• Rare Exceptions:
  • Some Fossils in Low-grade Metamorphic Rocks, Trees
  • Buried by Lava Flow

To Be Preserved, Organisms Have to Be:

• Buried Rapidly After Death
• Preserved From Decay

These Are Difficult Requirements! Probably Only One Organism in Millions Ever Gets Fossilized

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Good Index Fossils

• Abundant
• Widely-distributed (Global Preferred)
• Short-lived or Rapidly Changing

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Classification of Organisms (Taxonomy)

Classical System - Linnaeus, ca. 1760

• Kingdom - Animal or Plant?
  Humans and dogs are in the Animal Kingdom
• Phylum
  Humans and dogs are in the Phylum Chordata; they have a stiffening rod along their dorsal side.
• Class
  Humans and dogs are in the Class Mammalia; they have hair, warm blood, and nurse their young.
• Order
  Here humans and dogs part company:
  • Humans are in the Order Primata
  • Dogs are in the Order Carnivora
• Family
  • Humans are in the Family Hominidae
  • Dogs are in the Family Canidae
• Genus
  • Humans are in the Genus Homo
  • Dogs are in the Genus Canis
• Species
  • Humans are Homo sapiens
  • Dogs are Canis familiaris

Organisms are known by their genus and species names

Why use this system?

• Common organisms have names in many languages
• Sometimes different organisms are called by the same name in different places
• Often the same organism has different names in different places
• Rare, inconspicuous, and extinct organisms have no common names at all

Classification - The Modern System

Once upon a time, kingdoms were pretty trivial: Elephants were animals, Redwoods were plants. But in the last few decades the most interesting concepts in taxonomy have been happening at the highest levels.

For years, some biologists were frustrated by microorganisms that had characteristics of both animals and plants. They urged putting these organisms into a separate kingdom.

As long as we're on the subject, why are fungi plants? They don't respond to stimuli like animals, but they lack chlorophyll and most of the structures of green plants. Some biologists began treating fungi as a separate kingdom.

Bacteria differ from all other organisms. If fungi deserve a kingdom, so do bacteria. Thus, about 20 years ago, many biology texts adopted the

Five-Kingdom Classification

• Animals
• Plants
• Protists (one-celled microorganisms)
• Fungi
• Bacteria

Domains and Superkingdoms

Bacteria differ from all other organisms in not having a cell nucleus. Their DNA floats freely within the cell. The difference between bacteria and everything else suggests we need something even higher than the kingdom.

What's bigger than a kingdom? Maybe an empire, but most biologists prefer the term Domains. Some use Superkingdom. The current system of domains and kingdoms is:

• Domain Prokarya - Bacteria and blue-green algae
  • Several kingdoms to be defined
• Domain Archae - Primitive bacteria-like organisms
  • Several kingdoms to be defined
• Domain Eukarya
  • Kingdom Animalia
  • Kingdom Plantae
  • Kingdom Protista
  • Kingdom Fungi
  • Kingdom Ediacara? The Ediacaran fauna, named from a region in Australia, lived just before the start of the Cambrian and have now been found worldwide. They were very odd animals, up to a meter in size, with body plans totally unlike any living animals. They had no specialized feeding parts, so how did they live? Did they get nutrients directly from sea water, or from algae living within them? By analogy with fungi, why do we think these creatures were animals at all? Some biologists have proposed placing them in a new kingdom.

Why didn't Linnaeus think of this?

Easy. You need molecular biology and electron microscopes to see the defining characteristics at the domain level.

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Classification of Animals

There Are About 25 Phyla of Animals. Most Important Are:

Fossil representatives in parentheses

• Chordates - Mammals, Birds, Reptiles, Fish (Dinosaurs)
• Echinoderms - Starfish, Sand Dollars (Crinoids)
• Arthropods - Insects, Lobsters, Spiders, Crabs (Trilobites)
• Molluscs - Clams, Snails (Common)
• Brachiopods - Shelled Organisms (Common)
• Coelenterates - Jellyfish, Corals (Corals Are Common)
• Porifera - Sponges (Some Types Common)
• Protozoa - Single Cell, Mostly Microscopic (Foraminifera, Radiolaria) - Kingdom Protista in more modern schemes.

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Classificiation of Plants

There Are About Ten Plant Phyla - Most Important Are:

• Flowering Plants (Common)
• Cone-bearing Plants (Common)
• Ferns & Related Plants (Common especially in late Paleozoic)
• Horsetails & Scouring Rushes (Common especially in late Paleozoic)
• Mosses (Rare as fossils)
• Fungi (Mushrooms, Mold, Etc.- very rare as fossils) - A Kingdom in more modern schemes
• Algae (Some calcite secreting forms are common) - Kingdom Protista in more modern schemes
• Bacteria (Some preserved) - A Domain in more modern schemes

Plant Fossils Are Rarer Than Animal Fossils.
Leaves And Woody Parts of Higher Plants Most Common.

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Evolution

There Are Over 1,000,000 Species of Animals (90% of Them Are Insects!) And 350,000 Species of Plants

Scientists Believe All These Species Arose Through Evolution

Development of Evolution Theory

Early Developments

• Linnaeus C.1760
  Classification in Biology
• Hutton et Al C.1780
  Geology, Age of Earth
• Lamarck 1795
  Evolution by Acquired Characteristics

Originator of Modern Ideas on Evolution -Charles Darwin

• 1830's - Round-the-world Cruise on H.M.S. Beagle
• 1859 - Published Origin of Species
• Co-discovered by Alfred Russell Wallace
• Evolution by Natural Selection
  • Organisms Are Adapted to Their Environment
  • More Organisms Are Born Than Can Survive
  • Individuals Vary

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Natural Selection

• All Living Things Are Made up of Cells.
• Most Cells Have a Nucleus Which Contains a Complex Molecule Called DNA.
• The DNA in Cells Contains a "Code"
• When The Cell Multiples, The DNA Code Governs The Makeup of The New Cell.
• Sometimes The DNA Is Damaged by Chemicals or Radiation, or The DNA Code Isn't Copied Exactly in The New Cell. Either Way, The New Cell Is Slightly Different From The Old Cell. Such a Change Is Called a Mutation. 
• Mutations Cause DNA Code to Be Changed in Passing From Parent to Offspring.
• If Mutation Is Major, it Usually Causes Offspring to Be Less Well Adapted Than Parents. Mutation Tends to Die out.
• If Mutation Is Minor, Has Little Immediate Effect on Offspring. Mutation Doesn't Die Out, But Is Passed On.
• Most Organisms are already Well-Adapted, so any major change is likely to be harmful.
• There are no half-formed organisms. There is no such thing as "half an eye" or "half a wing." Early eyes and wings weren't as sophisticated as their later descendants but they gave their organisms advantages nevertheless.
• Mutations rarely have any immediate effect. If conditions change, then the mutation may be better for the organism, and those organisms without the mutation may die out.
• Very often, previously existing structures are put to new use, a process called exaptation. Amphibians already had legs before they left the water. The legs developed for locomotion along the bottom and perhaps locating food.

For the historical context and responses to evolution see:

• Social and historical context of Evolution
• Reactions to Evolution

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Mass Extinctions

Permian

• Trilobites
• Many Brachiopods
• Many Tree Ferns, Scale Trees
• Worst in Earth History - 90% of species

Cretaceous

• Dinosaurs
• Ammonites
• Moderately Bad - only 60% of species
• Three others as bad or worse

Causes ?

• Climate Change
• Disease
• Mountain-building
• Sea Level Change
• Competing Organisms
• Over-specialization
• Catastrophe
• Volcanism
• Meteor Impact

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Were the Dinosaurs Failures?

We often use the term "Dinosaur" to denote something clunky or obsolete, but consider:

Written History Lasted 5000 Years	The Dinosaurs Lasted 150,000,000 Years
For Every Year of written history:	The Dinosaurs had 30,000 Years
For Every Day of written history:	The Dinosaurs had 82 Years - a long human lifetime
For Every Minute of written history:	The Dinosaurs had 3 weeks
For Every Second of written history:	The Dinosaurs had 8.3 hours

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Created February 26, 1997; Last Update October 19, 1998