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

didelphimorph Opossums () are members of the marsupial order Didelphimorphia () endemic to the Americas. The largest order of marsupials in the Western Hemisphere, it comprises 93 species in 18 genera. Opossums originated in South America and entered North ...

marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a ...

. 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 ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

. The species is gaining popularity as a

pocket pet The most common rodents kept as household pets are hamsters (golden hamsters and dwarf hamsters), gerbils (Mongolian jirds and duprasi gerbils), common degus, fancy mice, fancy rats, common chinchillas, and guinea pigs (cavies). The domest ...

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 The 27 species in the genus ''Marmosa'' are relatively small Neotropical members of the family Didelphidae. This genus is one of three that are known as mouse opossums. The others are '' Thylamys'' (the "fat-tailed mouse opossums") and '' Tlacua ...

'', ''

Monodelphis ''Monodelphis'' is a genus of marsupials in the family Didelphidae, commonly referred to as short-tailed opossums. They are found throughout South America. , the most recently described species is ''M. vossi''. Species * Sepia short-tailed ...

'', '' Thylamys'', '' Tlacuatzin'', ''

Gracilinanus ''Gracilinanus'' is a genus of opossum in the family Didelphidae. It was separated from the genus ''Marmosa The 27 species in the genus ''Marmosa'' are relatively small Neotropical members of the family Didelphidae. This genus is one of t ...

'', '' Marmosops'', '' Lestodelphys'') in having a long third manual digit, no distinctly tricolored

pelage Fur is a thick growth of hair that covers the skin of 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 insulating blanket ...

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

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 South America Marsupials of Argentina Gran Chaco Mammals described in 1930