Mouse possums are relatively small members of the Neotropical marsupial family Didelphidae . Three genera are known: Marmosa (mouse possums), Thylamys (fat-tailed mouse possums) and Tlacuatzin (grayish mouse possums).
“Most Marmosa species are endemic to South America, and biogeographic reconstructions suggest that the genus evolved on that continent when it was still separated from North America by a seawater barrier,” says Robert Voss, curator of the Department of Mammalogy in the American Museum of Natural History. “Only a few species of Marmosa now belong to the North American fauna, but these include members of two subgenera.”
The new species, called Adler’s mouse opossum ( Marmosa adleri ), is among the smallest measures of the subgenus Micoureus. “In side-by-side morphological comparisons, Marmosa adleri could never be confused with its sister taxon, Alston’s mouse opossum ( Marmosa alstoni), ” the researchers said.
“ The difference in size alone is surprising; in fact, there is no overlap between most of the measurements of these species, and the average body weight of Marmosa adleri (58 g) is less than half that of Marmosa alstoni (137 g) ”.
The Adler’s mouse opossum has only been seen in Panama, but it is widely distributed within that country, from near the border with Costa Rica to the border with Colombia, and from near sea level to almost 1,500 meters.
“The discovery of this species is very unusual because I collected it in what may be the most studied tropical forest area in the world,” says Greg Adler, a researcher at the University of Wisconsin. “Numerous expeditions collected thousands of specimens there throughout the 20th century and they never found this species. It’s amazing that it has escaped discovery for so long. “
Referencia: Robert S. Voss et al. 2021. A revision of the didelphid marsupial genus Marmosa. Part 4, species of the Alstoni Group (subgenus Micoureus). American Museum Novitates 3983
