This Research in Action article was provided to LiveScience in partnership with the National Science Foundation.
This image shows a Zeledon's mouse opossumat La Selva Biological Station, Heredia province, Costa Rica, in August 2005.
Small enough to climb onto the inflorescence, or flower cluster, of a palm plant, this tiny mouse opossum belongs to a newly re-classified South American species: Zeledon's mouse opossum (Marmosa zeledoni). Minute marsupials like this one are rarely seen at flowers, but this species may be a pollinator for some neotropical palms.
Zeledon's mouse opossum was previously lumped together with the Mexican mouse opossum, Marmosa mexicana. But in a recent study partly funded by the National Science Foundation, Curator Rob Voss of the Division of Vertebrate Zoology at the American Museum of Natural History and colleagues examined roughly 1,500 mouse opossum specimens, some collected from as far back as the 1800s. They determined that what had been known as the Mexican mouse opossum could actually be subdivided into two different species.
The morphological differences between the two species, such as tooth shape, tail length and fur color, can be miniscule.
"This is true of many nocturnal mammals—they usually have very subtle external morphology characteristics," said Voss, who authored the study with Rogério Rossi of the Universidade Federal de Mato Grosso in Brazil, and Darrin Lunde, also of the American Museum of Natural History. Their results were published in June 2010 issue of the peer-reviewed Bulletin of the American Museum of Natural History.
The results have also been confirmed by molecular analysis in a separate study that was published in the peer-reviewed American Museum Novitates.
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