The Fossil Record

Outcrop area

Not all differences in regions due to collection bias, as not all layers of all ages are exposed in all areas

Single sites: preservation potential

Not all species in an ecosystem are preserved (ex. soft tissue is not preserved as well as hard, so soft tissue only species may have millions of years between appearances)

Open and deep ocean

Open and deep ocean formations are likely to be new, or can be subducted or remain buried

Taxonomic practices bias

Some groups are split into more species than others, traits used to name species in modern may not be apparent in fossils, so more diversity in a time period may be due to a greater splitting in species or opposite.

Correcting Taxonomic Bias

Studies tend to use higher levels, such as genera and families, as these are more stable over long periods and are more identifiable in the record

Lagerstatten effect

The existence of these sites drive up diversity, but many species only occur or are only identifiable at the single site

The Fossil Record is biased and incomplete due to..

fossilization is inconsistent so some part will always remain unknown

Correcting for Patchiness: Lazarus Taxa and Ghost Lineages

We can assume that species do not evolve more than once

Depositional Hiatus

A gap in rock record due to lack of sedimentation or previous erosion

Single sites: Lagerstatten

A site with exceptional preservation (ex. Burgess Shale site)

The fossil record is _____ than looking at living alone

Better; using living diversity alone would miss diversities due to changes in envrionment, etc

Single sites: death assemblages

Fossils tend to be found in specific locations of limited areas, but species may not have existed together in life

Correcting for Collection Bias: Collection Curves

Can check if diversity has been stable, or if a lot more species are left to be found

Modeling

Can compare fossil record to expectations under various scenarios

Correcting Preservation potential and collection bias

Can make assumptions from like-dead studies about what is likely to be missing

Origination and Extinction Rates

Can track changes in origination and extinction against other metrics

Collection Bias

Certain types of species have more active workers and are more likely to be names (Dinos vs. seastars), certain time periods have more workers, certain regions are more likely to be explored for fossils or have been more extensively sampled in the past (Victorian England)

Sea level

Changes in sea level shift areas of deposition; fall can stop sedimentation and destroy previous layers through erosion

Live-Dead Studies

Compare living assemblages to recently dead at different layers, can determine rate of fossilization and loss, tells us what is lost randomly and what is due to poor preservation in older layers in different environments

Rock volumes

Depositional changes affect the amount of fossil bearing rock, and diversity tends to correspond with available rock

Konzentrat-Lagerstatten

Sites with extreme abundance of hard tissue, high time averaging

Biodiversity through time

Increases and decreases due to changes in environment, extinction and origination, and fossilization and sampling biases

The Fossil Record

Is patchy, as fossils are not deposited evenly through time

Phylogeny and Divergence Dates

It is unlikely that the first appearance is the actual time of origination

Macrofossil vs. Microfossil Record

Macrofossils less likely to be preserved or identified, while microfossils are abundant in record but may not be matched to a species

Common Cause Hypothesis

Models suggested that the relationship between diversity and rock volumes was caused by common environmental factors affecting both sedimentation and biodiversity

Sedimentation Rate

Rate is dependent on erosion, sea level, volcanism, plankton abundance, etc, so it is not even at all times

Habitat bias

Sedimentation rate higher on shelf than other areas, so shelf diversity tends to look higher than open ocean or terrestrial diversities

Geologic Timescale

Shows biases of fossil record (Precambrian and Phanerozoic are the two supereons, but Precambrian is from 4.5 Ba to about 541 Ma while Phanerozoic is 541 Ma to present)

Potential sources of bias in fossil record

Single sites, taxonomic practices, collection biases, habitat biases, sedimentation rate

Konservat-Lagerstatten

Sites which preserve soft tissues and animals which are not normally fossilized

Single sites: time averaging

low sedimentation rates can compress thousands or millions of years into one layer, hiding changes