The history of biodiversity –based on counts of fossils sampled from the rock record and for most groups biodiversity patterns have been based on the fossil record available from land-based outcrops.
But there is a problem – a worrisome correlation exists between sampled diversity and the rock record driven by large transgression-regression cycles. As we have heard from Shanan this could be biological as much as sampling artefact - so what we need is another system where the rock record is very different so that we can resolve how important rock sampling is. Such a record exists! – in the deep-sea.
For microfossils such as coccolithophorids we have access to both a deep-sea record and a land-based record which gives us two biodiversity estimates under two different rock records which allows us to explore the relationship between rock & fossil records and pinpoint how much the rock record influences biodiversity curves. Today I’m going to concentrate on the deep sea
Comparing rock and fossil records in the deep sea
Comparing rock and fossil records in the deep seaGraeme T. Lloyd, Andrew B. Smith and Jeremy R. Young
Fossil record is our only record of the diversification of life
Diversity correlates with rock record on landPeters and Foote 2001 Smith and McGowan 2007
An alternative record• Calcareous microfossils such as coccolithophores have land-based and deep sea records• i.e., two diversity records and two rock records• What is the relationship between these records?• How much does the rock record influence diversity patterns?
The database• Study groups are Coccolithophores and planktic Foraminifera• Novel compilation from North Atlantic• Compiled from 40 years ODP/DSDP data• 64,077+ occs from 20,723+ samples• High temporal resolution (biozones)
Correlation tests• First both time series were log-transformed• Long term test: – Simple correlation• Short term tests: – First differences (absolute) – Moving average differences (relative to long term trend)• Degree (rho) and significance (p) of correlations determined using Spearman rank
Conclusions• Deep sea diversity curve largely explicable by sampling• Apparent rise in nannofossil diversity to present strongly associated with rise in sampling
The other side of the story• What about the land-based record for the same groups?• Sampling strategy based on distribution charts from primary literature• Rock record measure is number of localities
Summary• Both land and sea have measurable rock biases that follow different trajectories over geological time• Will allow a clear and explicit test of how important a role these play in shaping our fossil record