The Chacoan pygmy opossum (''Chacodelphys formosa'') is a recently described genus and species of didelphimorph

marsupial Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a r ...

. The only species in ''Chacodelphys'', ''C. formosa'', was known until 2004 from only one specimen collected in 1920 in the Chaco of

Formosa Province Formosa Province () is a province in northeastern Argentina, part of the Gran Chaco Region. Formosa's northeast end touches Asunción, Paraguay, and the province borders the provinces of Chaco and Salta to its south and west, respectively. The ...

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

Description

The Chacoan pygmy opossum is the smallest known species of didelphid. It has a head-body length of 68 mm, a tail of 55 mm and a hind foot of 11. It differs from the other " marmosine" genera ('' Marmosa'', '' Monodelphis'', '' Thylamys'', '' Tlacuatzin'', '' Gracilinanus'', '' Marmosops'', '' Lestodelphys'') in having a long third manual digit, no distinctly tricolored

pelage A fur is a soft, thick growth of hair that covers the skin of almost all mammals. It consists of a combination of oily guard hair on top and thick underfur beneath. The guard hair keeps moisture from reaching the skin; the underfur acts as an ...

, a long fourth pedal digit, and a tail shorter than head-body. No other marmosine genera has this combination of characters. It is

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

to a small region of northern

Taxonomic history

''C. formosa'' was originally described as ''Marmosa muscula'' Shamel (1930a); however, this name is preoccupied, so Shamel (1930b) renamed it ''M. formosa''. Afterwards, George Tate (1933) considered it a valid member of his "''Elegans'' group" (=''Thylamys'') of ''Marmosa'', whereafter it has been variously synonymized or treated as a distinct species of ''Marmosa'' or ''Thylamys'' until 1989, when Gardner & Creighton (1989) listed it as a synonym of ''Gracilinanus agilis'', and then later separated from this species as ''G. formosus''. Finally, Voss et al. (2004) erected the new genus ''Chacodelphys'' for the species.

References

*Gardner, A.L. & Creighton, G.K. 1989. A new generic name for Tate's microtarsus group of South American mouse opossums (Marsupialia: Didelphidae). ''Proceedings of the Biological Society of Washington'' 102:3–7. *Shamel, H.H. 1930a. A new murine opossum from Argentina. ''Journal of the Washington Academy of Sciences'' 20:83-84. *Shamel, H.H. 1930b. A new name for Marmosa muscula Shamel. ''Journal of Mammalogy'' 11:311. *Tate, G.H.H. 1933. A systematic revision of the marsupial genus Marmosa with a discussion of the adaptive radiation of the murine opossums (Marmosa). ''Bulletin of the American Museum of Natural History'' 66:1–250. *Voss, R.S., Gardner, A.L. & Jansa, S.A. 2004. On the relationships of "Marmosa" formosa Shamel 1930 (Marsupialia, Didelphidae), a phylogenetic puzzle from the chaco of northern Argentina. ''American Museum Novitates'' 3442:1-18, 2 June 2004. {{Taxonbar, from1=Q1058476, from2=Q18325039 Opossums Marsupials of Argentina Gran Chaco Mammals described in 1930