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Lab 2B: Fossil Preservation

Geology 1402

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What we will cover today…

• Definition of a fossil

• Limitations of the fossil record

• Modes of preservation

• Biochemical signatures and pseudofossils

• Fossil classification

• Symmetry

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The branch of geology that

studies fossils

• Paleontology

– Paleo- from the Greek palaios—ancient

– Ology- the study of

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What is a fossil?

• Remains or traces of organisms (plants,

animals, etc.)

• Preserved through natural processes

• Over 10,000 years old

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To be preserved—Two Things

• Hard parts (there are exceptions to this)

– Teeth

– Bones (endoskeletons)

– Shells (exoskeleton)

• Rapid burial (preserved from decay)

– Mud

– Clay

– Volcanic ash

– Marine (ocean) sediments

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The fossil record is incomplete…

• Few organisms with soft parts are preserved (jellyfish, insects and many plants)

• No organisms that decay before burial

• Shallow marine organisms are most likely to be buried rapidly

• Note:

– We have about 250,000 fossil species

– Today around 4,000,000 species exist

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Which is more likely to become a

fossil?

• Fish

• Rabbit

Modes of Preservation (There is a slide on each.)

• Unaltered preservation

• Replacement

• Recrystallization

• Permineralization

• Carbonization

• Indirect preservation

– Molds & casts

– Trace fossils

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To Petrify

• To turn into stone—several methods.

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Unaltered preservation

• Original material is preserved

– Frozen mammoths of Siberia (ice)

– The Ice Man in northern Italy (5,000 years old)

– Tigers and insects in tar pits (15,000 years old)

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Unaltered preservation (cont.)

• Original material is preserved

– Insects in amber (amber is…) (100 million

years old)

– Desiccation (drying out—becomes a mummy)

in desert areas (sloth found in volcanic vent—

35,000 years old)

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Recrystallization

• Change in crystal structure of minerals

• Detailed structure is lost

• For example: Calcite (rhombohedral crystal

form) can change to aragonite (cubic crystal

structure). (Both calcite and aragonite have

the same chemical formula.)

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Replacement

• Groundwater dissolves original material

molecule by molecule and replaces it with

another mineral. Great detail is preserved.

– Calcite shells dissolve or

– Woody parts of trees dissolve

– Quartz or pyrite deposited

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Permineralization

• Groundwater passes through porous

remains and

– original hard parts remain and

– additional mineral material deposited in the

pores.

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Carbonization

• Most common way soft parts are preserved

• High pressure and temperature after burial

drives off volatile substances (hydrogen,

oxygen, nitrogen) and leaves behind mostly

carbon.

• These are carbon films that preserve details

of original organism

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Indirect preservation

• Molds and Casts

– Groundwater dissolves buried shell material

and leaves a mold in the surrounding material

– The mold later becomes filled with sediment or

minerals and forms a cast—a replica of the

original shell

– Not good detail

– Example: Pompeii, Italy (79 A.D.)

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Indirect preservation

• Trace fossils—evidence that an organism was there

– Tracks

– Trails

– Burrows

– Coprolites (fossilized dung)

– Gastroliths (stomach stones)—swallowed to help digestion (dinosaurs and chickens)—pits etched by stomach acid and piles of 100 stones

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Indirect preservation

• Biochemical signatures (a type of trace

fossil)

– Carbon and sulfur with isotopic ratios

indicating living organisms

– DNA in soils

– Complex organic molecules

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Oldest evidence of life…

• Biochemical signatures

• Carbon spheres with isotopic signatures of

living organisms—3.9 billion years old

(organic origin is being debated)

• Undisputed organic carbon 3.7 billion year

old rocks

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Pseudofossils (fake fossils)

• Naturally occurring inorganic minerals or

rocks which are mistaken for true fossils.

– Manganese dendrites—mistaken for plant

fossils. Water moves through a fracture and

deposits pyrolucite (a dark mineral)

– Concretions (geodes)—mistaken for dinosaur

eggs

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Fossil classification

• Linnaean system—same used to classify

living organisms

• Uses morphologic (form) structure as basis

• Three Domains (Five kingdoms)

Linnaean Classification

• Kingdom

• Phylum

– Subphylum

• Class

• Order

• Family

• Genus

• species

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Linnaean Classification

• Species—

– Group of organisms

– Similar structure, function and development

– Able to produce fertile offspring (in nature)

• Examples of non-species:

– Mule (female horse and male donkey)

– Liger (tiger and lion—only happens in zoos)

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Linnaean Classification

• Refer to an organism by genus and species.

• Genus capitalized; species lower case; both

italics

• Example: Homo sapiens

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Symmetry of invertebrate fossils

• No backbone or spinal column

• Symmetry—orderly arrangement of parts in

relation to lines, planes or points

– Radial

– Bilateral

– No apparent symmetry

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Types of Symmetry

• Radial symmetry: repetition around an axis

– Round birthday cake and pizzas

– Starfish and echinoids

• Bilateral symmetry: duplicate parts on each

side of a plane (like people)

– Clams

– Snails

Radial symmetry Bilateral Symmetry

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No Symmetry

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Any questions?

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