Biostratigraphy

Staatliches Museum für Naturkunde Stuttgart

Amoeboceras bauhini: Amoeboceras bauhini

I. IntroA. Aim is to establish

correlations between time-equivalent strata by presence of a particular fossil species.

B. generally straightforward, i.e. presence of a specific fossil species in two geographic localities indicates the rocks containing the fossil specimens were deposited at about the same timeA. in practice

biostratigraphic studies tend to be complex

II. What is a Fossil?

A. Term fossil from Latin word for "dug up,"

B. originally -- anything dug out of the earth.

C. Today, refers to remains or other evidence of ancient life forms. Generally, more than about ten thousand years old

Hussam Zaher / University of Sao Paulo via AP

updated 10:08 a.m. PT, Wed., April 19, 2006

NEW YORK - A new fossil discovery has revealed the most primitive snake known, a crawling creature with two legs, and it provides new evidence that snakes evolved on land rather than in the sea. Snakes are thought to have evolved from four-legged lizards, losing their legs over time. But scientists have long debated whether those ancestral lizards were land-based or marine creatures. The new find reveals a snake that lived in the Patagonia region of Argentina some 90 million years ago, said Hussam Zaher of the University of Sao Paulo in Brazil, who describes the find in Thursday's issue of the journal Nature. Its size is unknown, but it wasn't more than 3 feet long, he said in a telephone interview.

III. Index FossilsA. Used to establish correlationB. Critieria

1. must have a widespread distribution

Most limited to a small region or found only in particular depositional environment)

2. must show rapid evolution 3. must be present in

substantial numbers 4. fossils should be robust

mineralogically so that depositional and diagenetic processes do not remove the fossils from the rock record).

5.Best index fossils are planktonic or nektonic

6.benthic organisms, tend to be less widespread, fewer in numbers, and typically found in particular environments

IV. Origin & Basis of Biostratigraphy

A. William “Strata” Smith (1769-1839)1. orderly succession

in fossil2. correlated rks

w/fossilsi. major advance

3. major achievements followed --maps

Biostrat ContinuedB. Principle of Faunal

Succession1.Non-reversible

evolutionary change

2. species had limited existence

3. species fundamental taxon

Biostrat ContC. Biozone

1. rk defined by presence, absence, relative abundance of certain species or other taxa or of assemblages of species or other taxa

Biostrat ContD. d’Orbigny used stages/zones

1. zones subdivision of stages2. defined zone fossils

IV Biozone Types

A. 3 major types1. Interval2. Assemblage3. Abundance

B. Interval zone1. taxon range zone

i. max stratigraphic range of species, taxon

2. concurrent & partial range zone

i. interval of overlap between 1st appearance of one species & last appearance of different taxaii. also uses gaps--partial range zones

3. InterzonesI. barron interzonesii. unfossiliferous

zones delineated by biozones above & below

4. lineage zonei. evolutionary

connectionii interval between

last appearance of one taxa and first appearance of descendent

C. Assemblage zone1 biozone characterized by association of 3+ taxa

i unique and distinguishable form assemblage above and belowii biocoenosisiii thanatocoenosis

a. problem--reworking of older strata

D. Abundance zone1. strata containing maximum abundance in numbers of individuals of one or more species or taxa.2. acme zone3. difficult to use4. sparseness above and below due to sed environment, preservation, etc.

i. correlation risky

V. Correlation Problems

A. Subjective taxonomic proceduresB. Missing Taxa

1. generate gaps in range zones2. facies control3. not preserved4. rare (missed)5. misidentified

C. No agreement on zone

Fossil Record BiasFOSSILS IN STRATIGRAPHY• Abundance and size: smaller fossils are moreabundant than larger ones, thus are moreuseful in biostratigraphy• Preservation Potential: Fossil recordrepresents only a minor portion of the past lifebecause (a) only hard parts are fossilized withfew exceptions (b) different environments havedifferent fossilizable potential (c) stratigraphicrecord is incomplete, only few environmentalniches are preserved in sedimentary rocks• Rate of Speciation: Differing rates ofspeciation observed in fossil record

A. SPECIES CONCEPT IN PALEONTOLOGYSpecies is the basic unit biological classification, i.e. organisms can be related to each other in a hierarchical manner. It is also used to classify fossils• Kingdom• Phylum• Class• Order• Family• Genus• Species

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Interval Zones

Interval Zone

Interval Zone

Taxon Range Zone

Concurrent Range Zone

Lineage Zone

Assemblage Zone

Assemblage Zone

Barron Zone

Abundance Zone