Wednesday, October 13, 2010

Fossil of the Week

10/13/10 –Tropical Antarctica?
In a salute to Museum of the Earth’s new exhibition “Science on the Half Shell: How and Why We Study Evolution” (created by PRI’s Bivalve Evolution project), this week’s fossil of the week is Lahillia wilckensi Zinsmeister, 1984 (PRI 13176). Lahillia is a heart cockle, a member of the bivalve family Cardiidae. This group of clams still living today is prevalent in the tropics and subtropics of the world’s oceans. What is special about Lahillia is that it was discovered and described from Eocene deposits in Antarctica – a decidedly un-tropical location today!

The world during the Eocene Period, 56 to 34 million years ago, was very different from the modern world. Globally, it was a very warm “hothouse” world – the air temperature difference from pole to equator was only half of today’s and the deep-ocean currents were exceptionally warm. Tropical climates extended as far north as Maine and Hokkaido, Japan. On a map of Eocene Earth, most of the modern continents are recognizable, but they have not yet moved to their present positions. There are no polar ice caps, India is still free-floating, and Europe and Asia are bisected by the large shallow Paratethys Sea. The Paratethys was a center of origin for many tropical Pacific bivalves, including Giant Clams, which are now restricted to coral reefs in the Indo-West Pacific.

Lahillia wilckensi was described by Dr. William J. Zinsmeister, a professor of geology at Purdue University. It was collected during a 1974-1975 joint Argentine-American expedition to Seymour Island. PRI received Professor Zinsmeister’s entire research collection in April 2009, and just recently was awarded National Science Foundation funding to curate the collection. The Zinsmeister Collection contains approximately 5,510 lots (almost 22,000 specimens) of Cretaceous-to-Eocene fossil mollusks from Seymour Island, Antarctica, and its vicinity, and is widely recognized as among the largest and finest in the world from this region. The Seymour Island fossil fauna contains species from both southern South America and Australasia and provides the key to understanding the biogeography of the southern Pacific Ocean during the final break-up of the ancient continent Gondwana.

Text by Paula Mikkelsen

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