Cryptonanus

''Cryptonanus'' is a genus of opossums from South America. It includes five species found from Bolivia to Uruguay and eastern Brazil, one of which is now extinct. Although the first species were discovered in 1931, the genus was not recognized as distinct from '' Gracilinanus'' until 2005. It includes small opossums with generally grayish, sometimes reddish, fur that are mainly distinguished from other opossums by characters of the skull.

Taxonomy

Species of ''Cryptonanus'' were first described in 1931 by George Henry Hamilton Tate,Voss et al., 2005, p. 5 who described ''Marmosa microtarsus guahybae'' (now '' Cryptonanus guahybae'') as a subspecies of ''Marmosa microtarsus'' (now '' Gracilinanus microtarsus''), ''Marmosa agilis chacoensis'' (now '' Cryptonanus chacoensis'') as a subspecies of ''Marmosa agilis'' (now ''Gracilinanus agilis''),Tate, 1931, p. 10 and ''Marmosa unduaviensis'' (now '' Cryptonanus unduaviensis'') as a separate species.Tate, 1931, p. 11 In 1943, another species was described, ''Marmosa agricolai'' (now '' Cryptonanus agricolai'').Gardner, 2009, p. 41 Species of ''Cryptonanus'' were then included in a broadly defined genus ''Marmosa'' until the genus '' Gracilinanus'' was described in 1989. The fifth currently recognized ''Cryptonanus'' species, '' C. ignitus'', was described as a species of ''Gracilinanus'' in 2002. At that time, the species of ''Cryptonanus'' were variously regarded as separate species or as synonyms or subspecies of other species of ''Gracilinanus''.Gardner, 2009, p. 40

Robert Voss and others noticed that some of the animals then classified in ''Gracilinanus'' had an additional foramen ovale, an opening in the skull that is formed by an extension of the bone of the alisphenoid tympanic wing towards the middle and front. They looked for other characters that correlated with the presence of the foramen and found them easy to find, defining a group of species distinct from ''Gracilinanus''.Voss et al., 2005, p. 2 A phylogenetic analysis corroborated the distinctness of ''Cryptonanus'' and ''Gracilinanus''.Voss et al., 2005, fig. 4 Voss and colleagues first noted the discovery in a footnote in their 2004 paper on '' Chacodelphys'' and subsequently described the group of species with the additional foramen as a new genus, ''Cryptonanus''. The generic name, ''Cryptonanus'' is derived from the Ancient Greek words κρυπτος ''kryptos'' (hidden) and νανος ''nanos'' (dwarf) and was chosen because ''Cryptonanus'' species are small and their true identity was long hidden by taxonomic synonymy.Voss et al., 2005, p. 11 ''Cryptonanus'' is currently classified in the tribe Thylamyini of subfamily Didelphinae within the opossums.

Voss and colleagues recognized each of the five names they referred to ''Cryptonanus''—''agricolai, chacoensis, guahybae, ignitus'', and ''unduaviensis''—as separate species, although they could find few distinguishing characters between them. Further research in this matter is needed.Voss and Jansa, 2009, p. 128

Species

Cladogram of living ''Cryptonanus'' species.

The five species currently recognized are:

Description

''Cryptonanus'' species are small opossums even within their family and weigh about . The fur is unpatterned and usually reddish or grayish brown above and is grayish or unpigmented below. Guard hairs are poorly developed. A dark ring surrounds the eyes. On the forefeet, the third and fourth digits are longer than the second and fifth. Females lack a pouch and have 9 to 15 mammae. The tail looks naked to the unaided eye, but each scale in fact harbors three short hairs. Species of ''Cryptonanus'' and ''Gracilinanus'' are hardly distinguishable on external characters, though ''Cryptonanus'' species may have shorter tails, larger ears, broader eye-rings, and longer whiskers. More secure characters separate the skulls of the two genera.Voss et al., 2005, p. 6 In addition to the presence of the additional foramen ovale, which exhibits some variation within species, ''Cryptonanus'' usually lacks maxillary fenestrae, perforations of the palate near the first and second molars, has the second upper premolar shorter than the third,Voss et al., 2005, p. 7 lacks a rostral process, which extends the premaxillary bone further to the front, and usually has additional cusps on the upper canine tooth. The species of ''Cryptonanus'' differ in coloration, size, and some characters of the teeth.

The karyotype of ''C. agricolai'' includes 14 chromosomes with 24 major arms (2n = 14, FN = 24).Voss et al., 2005, p. 14

References

Literature cited

*Diaz M. and Barquez, R. 2008. . In IUCN. IUCN Red List of Threatened Species. Version 2009.2.
www.iucnredlist.org
. Downloaded on March 26, 2010.
*Gardner, A.L. 2009. Mammals of South America. Volume 1: Marsupials, xenarthrans, shrews, and bats. University of Chicago Press, 669 pp.
*Tate, G.H.H. 1931
Brief diagnoses of twenty-six apparently new forms of ''Marmosa'' (Marsupialia) from South America
''American Museum Novitates'' 493:1–14.
*Voss, R.S. and Jansa, S.A. 2009
Phylogenetic relationships and classification of didelphid marsupials, an extant radiation of New World metatherian mammals
''Bulletin of the American Museum of Natural History'' 322:1–177.
*Voss, R.S., Lunde, D.P. and Jansa, S.A. 2005
On the contents of ''Gracilinanus'' Gardner & Creighton, 1989, with the description of a previously unrecognized clade of small didelphid marsupials
''American Museum Novitates'' 3482:1–34.
*Voss, R.S., Gardner, A.L. and 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.

{{Taxonbar, from=Q311590

Opossums
Marsupial genera