Oldest species of marine mollusc discovered in Iberian Peninsula

Wednesday, February 23, 2011

WASHINGTON - A new species of mollusc - thought to be the oldest in its genus - has been discovered from various parts of the Iberian Peninsula.

Discovered in 2007, the new species Polyconites hadriani has been crowned the oldest in the Polyconites genus of the family Polyconitidae (rudists), a kind of extinct sea mollusc.

Till date, scientists had thought that the oldest mollusc in this genus was Polyconites verneuili.

“P. hadriani is similar in shape to P. verneuili, but it is smaller (with a 30mm smaller diameter), and with a thinner calcite layer to its shell (around 3mm difference),” said Eulalia Gili, one of the authors of the study and a researcher at the Department of Geology of the Autonomous University of Barcelona.

Gili said the new species was found in several parts of the Iberian Peninsula - in the Maestrat basin, the Vasco-Cantabrica basin, to the south of the Lusitania basin and in the Cordillera Prebetica mountain range, ‘where it accumulated in dense conglomerations along the banks of the carbonate marine platforms of the Lower Aptian period (114 million years ago)’.

“This recognition of P. hadriani resolves the lengthy uncertainty about the identity of these polyconitids of the Lower Aptian,” he added.

Researchers said the new species adapted to the acidification of the oceans that took place while it was in existence.

This process could now determine the evolution of modern marine systems.

According to Gili, the Lower Aptian was a convulsive period, during which significant climate change took place.

P. hadriani existed at the time when the first oceanic anoxic event of the Cretaceous took place (between 135 and 65 million years ago).

This event was characterised by a ‘lack of oxygen on the seabed, which led to the mass burial of organic carbon and climate cooling’.

“The thicker calcite layer of the shell of this new species compared with that of its predecessor (of the Horiopleura genus), could have helped it adapt better to life in colder waters, which were more acidic due to the increased solubility of atmospheric CO2,” said Gili.

The finding has been published in the Turkish Journal of Earth Sciences. (ANI)

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