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Postdoctoral research visitor Ceran Sekeryapan from Turkey has been studying lacustrine ostracods from our collections over the past week with the intention of adding records to the database of Non-Marine Ostracod Distribution in Europe (NODE). This database, combined with details of modern climate records and Geographical Information System (GIS) software is increasingly being used to reconstruct past air temperatures.

 

 

Cypris pubera, a freshwater ostracod (courtesy of Dr David Horne).

 

  • Ostracods and temperature

 

It has long been known that some non-marine ostracod species prefer colder while others prefer warmer climates. The Mutual Ostracod Temperature Range (MOTR) method, developed by Dr David Horne at Queen Mary University of London, calibrates each species by calculating the range of air temperatures that they can tolerate. This is done by plotting the present geographical distribution of each species and using detailed modern records of climate in these locations to calculate a seasonal air temperature range.

 

Other factors affect the distribution of ostracods, for example the chemisty, depth and hydrology of different water bodies harbouring ostracods.

 

  • Reconstructing past climates

 

Many species present in the modern day are also present in the Quaternary fossil record covering the last 2.5 million years. The MOTR method plots air temperature ranges of each species present in a fossil assemblage so that a mutual temperature range can be derived.

 

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Temperature ranges of non marine ostracod species identified by Horton et al. (1992) from a Hoxnian site about 400,000 years old at Woodston, Peterborough. The mutual temperature range for the month of January is calculated and shows slightly lower mean temperatures than the present day (courtesy of Dr David Horne).

 

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The same species are plotted for July and show temperatures similar or slightly warmer than the present, a seasonal conclusion in general agreement with studies on plant macrofossils, pollen and molluscs (courtesy of Dr David Horne).

 

  • Developing our collections

 

Ceran has been identifying species part of a large microfossil collection donated in 1991 by Prof. John Neale of the University of Hull. As well as providing new identifications and ratifying previous interpretations, she will provide new latitude and longitude references for the sites that our material has come from using a method called georeferencing. Modern maps and available resources like Google Earth are used to provide up to date latitude and longitude readings that were not present in the original data.

 

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Coverage of Recent non marine ostracod records in the OMEGA database (courtesy of Dr David Horne).

 

  • The global picture

 

Key data from the NODE database and other large datasets from Canada, USA, southern Africa and Japan are being assembled in OMEGA (Ostracod Metadatabase of Environmental and Geographical Attributes). This will facilitate improved calibrations as well as biogeographical and biodiversity research. Details from large museum collections like ours are continually being used in this work.

 

  • The future

 

Testing and refinement of the MOTR method can only make this climate interpretation tool more accurate in the future. Ceran will be applying this method and gathering more data from sites in Turkey. Contributions to the OMEGA database are also invited as part of a citizen science project. Museum collections are also set to play a vital role in this study.

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In 2011 we accepted a donation of 2,500 microscope slides containing over 90,000 ostracods from the personal collection of Prof. Richard Dingle. Richard has been visiting the Museum for almost 10 years now and has organised, documented and subsequently donated this major collection.

 

The material in the collection represents a lifetime of work on ostracods and underpins research that has helped illuminate some major questions in evolution, detailed the movements of ancient continents and shown patterns of migration of ostracods across oceans. Some important type specimens are also included in the collection.

 

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One of the slides that Richard has prepared before donation to the Museum. The total length is 7cm. Each of these specimens has been positioned on the slides during visits to the Museum by Richard; a very time consuming and painstaking process.

 

 

  • The opening of the Atlantic Ocean


From the late Jurassic (very roughly 150 million years ago) the ancient continental mass of Gondwana began to split, creating the Atlantic and Indian oceans. This left the Agulhus Bank off the tip of southern Africa in a central "cross roads" location between warm and cold waters, a situation that persists to the modern day.

 

 

Richard was able to show that mid Cretaceous South African ostracod faunas were similar to those of the Falklands, indicating the presence of an Agulhus Bank/Falkland Plateau prior to the plates separating and creating the present day Atlantic Ocean.

 

 

  • How and when do ostracod species migrate across oceans?

 


Studying the benthic (bottom dwelling) ostracods from the Agulhus Bank enabled Richard to document the influx of Madagascan type faunas from the emerging Indian Ocean and their onward passage to South America.

 

 

Various oceanic barriers to migration existed and were subsequently bridged. The ostracod faunas were able to show the timing of the influx of south/central Atlantic faunas into the SW Indian Ocean.

 

 

 

Richard's work has also contributed to various theories about the migration and sometimes isolation of ostracods lineages across oceans by island hopping. The collection also shows the migration of the important genus Magungaella from pre-glacial to younger glacial high latitude sites.

 

 

 

  • Can evolution work in reverse?

 

In a nutshell, Dollo's Law suggests that once an evolutionary trait has evolved, it can't be un-evolved. Richard's collection of ostracods from Marion Island in the Southern Ocean, shows the re-appearance of eyes in deep water ostracod genera that were previousy considered blind.

 

Richard proposed a gene-reactivation hypothesis to account for this. The possession of eyes is key to classifying ostracods and evaluating their evolutionary history, a matter of continuing controversy amongst ostracod workers.

 

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An example of Poseidonamicus, one of the deep sea genera of blind ostracods used by Richard Dingle to show that sightedness returned later in geological time in shallow water forms. This example is from the Aberystwyth Collection and photographed by Gene Hunt now at the Smithsonian Institution, Washington.

 


 

  • What do ostracods tell us about ancient environments and oceans?


It has been suggested that 40 million years ago there was a major global deep sea event that caused a disruption in deep sea populations. Richard's findings derived from Ocean Drilling Programme/ Deep Sea Drilling Programme collection sites, have contributed to discussions and conclusions about this ancient event.

 

The collection now at the Museum also provides the source data for Richard's triangulation method of palaeo-environment prediction, based on late Cretaceous (roughly 70-85 million year old) ostracods.

 

Similarly, Richard proposed that ostracod provinces existed around the margins of the ancient continental mass of Gondwana. Examples of these assemblages are also present in the collections he donated to the Museum.

 

 

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The collection that Richard donated is vast in terms of numbers of specimens and represents a lifetime of work on ostracods. Hopefully it will be remembered not only for the large number of items present but also for the excellent science it backs up. More about Richard Dingle's Collection and his work can be found in a paper published this month in the Journal of Micropalaeontology.

Giles Miller

Giles Miller

Member since: Apr 21, 2010

This is Giles Miller's Curator of Micropalaeontology blog. I make the Museum micropalaeontology collections available to visitors from all over the world, publish articles on the collections, give public talks and occasionally make collections myself.

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