Cryptonanus guahybae ( Tate, 1931 )

VOSS, ROBERT S., LUNDE, DARRIN P. & JANSA, SHARON A., 2005, On the Contents of Gracilinanus Gardner and Creighton, 1989, with the Description of a Previously Unrecognized Clade of Small Didelphid Marsupials, American Museum Novitates 3482, pp. 1-35 : 15-17

Cryptonanus guahybae ( Tate, 1931)

Marmosa microtarsus guahybae Tate, 1931: 10 . Original description based on the holotype (by original designation: ZMB 4306 ) collected on the island of Guahiba near Porto Alegre, Rio Grande do Sul, Brazil, and eight paratypes.

Marmosa (Thylamys) microtarsus guahybae: Cabrera, 1958: 31 . New name combination.

Gracilinanus microtarsus: Gardner and Creighton, 1989: 6 (part). New name combination.

IDENTIFICATION AND DISTRIBUTION: Based on Tate’s (1931, 1933) accounts and our examination of two paratypes, Cryptonanus

8 Five specimens of Gracilinanus agilis (BMNH 3.2.3.39, 3.4.7.22, 3.4.7.23, 4.1.5.46, 4.1.5.47) were collected at Sapucay by William Foster between 7 September 1902 and 13 May 1903, whereas two Sapucay specimens of Cryptonanus chacoensis (BMNH 4.1.5.48, 5.8.1.8) were taken by the same collector on 10 August and 11 September 1903. The separate calendar intervals represented by these dates suggest that Foster might have shifted his collecting activities near Sapucay during the intervening three­month period, but we are not aware of any documentary evidence to support or refute this conjecture.

TABLE 6 External and Craniodental Measurements (mm) and Weights (g) of Cryptonanus chacoensis guahybae is a distinctively reddish form with gray­ based buffy underparts that differs conspicuously in coloration from other congeneric taxa (all of which have duller, usually brownish or grayish­brown dorsal fur and much paler, usually self­whitish ventral fur). Although overlapping broadly with C. agricolai and C. chacoensis in all measured dimensions (tables 5–7), C. guahybae has a geographically discrete distribution (all referred specimens are from Rio Grande do Sul), and other trenchant differences may emerge from side­by­side comparisons of fresh material. In particular, mammary counts may be diagnostic. In the material we examined, one fluid­preserved female specimen of C. guahybae ( BMNH 82.9.30.42) has 7–1–7 5 15 mammae, of which the anteriormost three pairs are ‘‘pectoral’’ (arranged in parallel series anterior to the circular array of abdominal/inguinal teats; see Tate, 1933: fig. 3), whereas a fluid­preserved female specimen of C. chacoensis ( UMMZ 134552) has 4–1–4 5 9 mammae, all of which are abdominal/inguinal.

SPECIMENS EXAMINED: Brazil — Rio Grande do

Sul, São Lourenço ( USNM 236677), Taquara ( BMNH 82.9.30.42).

Cryptonanus ignitus ( Díaz, Flores, and Barquez, 2002)

Gracilinanus ignitus Díaz, Flores, and Barquez, 2002: 825 . Original description based on the holotype (by original designation: AMNH 167852 ) collected at Yuto , Departamento Ledesma, Provincia Jujuy, Argentina.

IDENTIFICATION: The holotype and only known specimen of Cryptonanus ignitus ( AMNH 167852 ), collected in the northwestern Argentinian province of Jujuy, is an unusually large animal (table 8) with several qualitative traits that set it apart from most other congeneric material that we have examined. In particular, the ventral fur is selforange (‘‘clay colored’’ sensu Díaz et al., 2002) from chin to anus with a prominent mid­pectoral blaze of self­white hairs. In addition, the zygomatic arches are unusually wide and robust, and the postorbital process of the jugal is massively developed. Other unusual features include prominent temporal

TABLE 7 External and Craniodental Measurements (mm) of Cryptonanus guahybae (Both specimens are paratypes from Rio Grande do Sul, Brazil.)

scars that extend posteriorly from the postorbital region along the dorsolateral contour of the relatively small braincase to merge with well­developed lambdoidal crests near the dorsal apex of the occiput. The upper canines are very long, and the palatine fenestrae consist of two small holes on each side of the palate rather than the single large hole seen in most congeneric specimens.

Despite this impressive list of distinctive attributes, however, we note that AMNH 167852 is a very old adult male (as indicated by its heavily worn molars and fused basioccipital/basisphenoid suture) and that some of its peculiar features are age­correlated in other didelphid taxa. Large ontogenetic series of most opossums, for example, show a tendency for older animals to have better­developed temporal scars, lambdoidal crests, and more massive zygomatic arches, but relatively smaller braincases than younger conspecifics (e.g., Tate, 1933; Abdala et al., 2001; Flores et al., 2003). In addition, the canine fangs of old adult male didelphids are often extruded from their alveoli to a much greater extent than in conspecific females and younger males.

The holotype of Cryptonanus ignitus was collected sympatrically with C. chacoensis (represented in our material by AMNH 167851, a subadult female), and the latter species has also been taken elsewhere in Jujuy (e.g., AMNH 185270). Given the ontogenetic interpretation of some traits exhibited by the holotype of ignitus , the hypothesis that this specimen is just an elderly example of chacoensis merits consideration. Indeed, although the holotype of ignitus is larger than any specimens herein referred to chacoensis in most measurements, ontogenetically invariant dimensions of the molar dentition (LM, M1–M3) are similar in both forms (tables 6, 8).

Díaz et al. (2002) did not explicitly compare iginitus with chacoensis because they regarded the latter form as conspecific with Gracilinanus agilis following then­current usage. Our side­by­side comparisons of AMNH 167852 with representative material of chacoensis do not reveal any consistent craniodental differences that cannot plausibly be attributed to age. However, the ventral pelage coloration of ignitus is unmatched by any specimens of chacoensis that we have yet examined, and on that basis we prefer to retain Cryptonanus ignitus as a valid binomen pending the results of ongoing fieldwork to obtain additional specimens (R.M. Barquez, personal commun.).

SPECIMENS EXAMINED: Argentina — Jujuy, Yuto ( AMNH 167852 ) .