Friday 20 December 2013

A new species of Ant from late Eocene Danish Amber.

Ants are among the most widespread and abundant of Insect groups, with over 13 000 described species. They play a major role in the shaping of modern ecosystems and landscapes, and many other species of animals, plants and even fungi have commensal relationships with Ant species and could not survive without them. Ants become common inclusions in amber from the Miocene onwards, suggesting they underwent a successful adaptive radiation at this time, but earlier Ants are poorly understood. Ants are believed to have derived from Wasp ancestors between 115 and 135 million years ago, although the oldest Ant fossils are only around 100 million years old, and these are rare. 

In a forthcoming paper in the journal Acta Palaeontologica Polonica, available online since 11 April 2013, Gennady Dlussky of the Faculty of Biology at Lomonosov Moscow State UniversityAlexander Radchenko of the Museum and Institute of Zoology at the Polish Academy of Sciences, and Dmitry Dubovikoff of the Faculty of Biology & Soil Science at Saint Petersburg State University, describe a new species of Ant from late Eocene amber from Denmark.

The new species is named Usomyrma mirabilis, where 'Usomyrma' means 'Ant with a moustache' or 'Ant with antennae' (the terms are apparently interchangeable in Russian) and 'mirabilis' means 'miraculous' or 'wonderful'. The species is based upon two specimens, both male, collected in the 1960s by B√≥rge Martensen from an unknown location in Denmark, and housed in the Zoological Museum of the University of Copenhagen. Despite the lack of a known locality of origin, the specimens are thought to be late Eocene in age, since all known sources of Baltic amber are of this age (not knowing the precise location from which Baltic amber originates is neither unusual nor generally thought a problem, since the amber floats and often turns up on beaches).

Usomyrma mirabilis is a 3.5 mm Ant with 13-segmented antennae, the second segment of which is extremely elongate and curved, a feature seen only in some modern Ants of the genus Leptomyrmex, which is now strictly Australasian in distribution, but which is judged to be the closest living relative of Usomyrma mirabilis, based upon the structure of the antennae and the venation of the wings. Two previous fossil members of the genus Leptomyrmex have been found in amber from outside of Australasia, one from the early Oligocene of Italy and one from Miocene Dominican Amber, leading to speculation that the group could have arisen in South America, and subsequently distributed to Europe and Australia. This discovery of an earlier European member of the lineage suggests that this scenario is wrong, and Dlussky et al. suggest that it is more likely the group arose first in Eurasia, and either reached Australasia via Southeast Asia and the Caribbean  North America separately, or  first reached Australia then the Caribbean via Antarctica and South America (which were formerly connected).

Usomyrma mirabilis, in lateral view. Photograph (top) and line drawing (bottom). Dlussky et al. (2013).

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