Cryptonanus, VOSS & LUNDE & JANSA, 2005

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 : 5-11

Cryptonanus , new genus

Figures 1A, 1B , 2A , 3A

TYPE SPECIES: Cryptonanus chacoensis

( Tate, 1931), originally described as a subspecies of Marmosa agilis (Burmeister, 1854) .

CONTENTS: We refer five nominal taxa to Cryptonanus , including chacoensis Tate (1931) , guahybae Tate (1931) , unduaviensis Tate (1931) , agricolai Moojen (1943) , and ignitus Díaz et al. (2002) . Despite the absence of unambiguously diagnostic characters in the small series we examined, it seems appropriate to accept provisionally the null hypothesis that all of these names represent valid species. However, in the event that chacoensis , guahybae , and unduaviensis —all named in the same publication ( Tate, 1931) and therefore having equal priority—should prove to be conspecific, we select chacoensis to have precedence under Article 24.2 of the International Code of Zoological Nomenclature ( ICZN, 1999).

MORPHOLOGICAL DIAGNOSIS: Species of Cryptonanus are small (15–40 g) didelphid marsupials that can be distinguished from other confamilial taxa by the following combination of qualitative morphological character states (see Voss and Jansa [2003] for character definitions and anatomical terminology).

Ventral margin of rhinarium with two shallow grooves on each side of median sulcus; eye narrowly surrounded by mask of dark fur contrasting in color with paler fur of cheeks and crown; pale spot above eye absent; dark midrostral stripe absent; gular gland present in adult males; dorsal body pelage unpatterned, usually grayish­ or reddish­brown; dorsal fur gray­based; dorsal guard hairs very short and inconspicuous; ventral fur graybased or self­colored (varying among species); manual digits III and IV subequal and longer than adjacent digits (II and V); manual claws shorter than fleshy digital pads; central palmar surface of manus sparsely tubercular (neither smooth nor densely covered with convex tubercles); lateral carpal tubercles present in adult males; pedal digit IV longer than adjacent digits III and V; plantar epithelium of pes naked from heel to toes; pouch absent; mammary complements differing among species, from 4–1–4 5 9 (without pectoral teats) to 7–1–7 5 15 (with pectoral teats); cloaca present; tail macroscopically naked but sparsely covered by short subequal hairs (three per caudal scale); caudal integument more­or­less bicolored (dark above, paler below) in most specimens; caudal scales in distinctly annular series; caudal prehensile surface present (the ventral surface naked distally, with an apical pad bearing dermatoglyphs); tail not incrassate.

Rostral process of premaxillae absent; palatal process of premaxilla contacts C1 alveolus on each side; nasal tips extend anterior to I1; nasals conspicuously wider posteriorly than anteriorly; maxillary turbinals large and elaborately branched; supraorbital margins rounded, without beads or processes (except in a few very old specimens with incipient postorbital processes and temporal scars); distinct interorbital and postorbital constrictions usually present in juveniles and young adults; sagittal crest absent; parietal and alisphenoid in contact (no squamosal­frontal contact); petrosal laterally exposed in fenestra between parietal and squamosal; maxillopalatine fenestrae large; palatine fenestrae present; maxillary fenestrae absent; posterolateral palatal foramina not extending lingual to M4 protocones; posterior palate with prominent lateral corners, the internal choanae abruptly constricted behind; maxillary and alisphenoid not in contact on orbital floor; transverse canal foramen present; secondary foramen ovale absent (anteromedial process of alisphenoid tympanic wing incomplete or absent); ectotympanic suspension direct; fenestra cochleae laterally exposed; paroccipital process of exoccipital small, adnate to petrosal; dorsal margin of foramen magnum formed by supraoccipital and exoccipitals; triangular stapes perforated by large foramen; two mental foramina on lateral aspect of each hemimandible; angular process acute and strongly inflected.

Unworn crowns of I2–I5 symmetrically rhomboidal, slightly increasing in breadth from front to back (I2 # I5); unworn C1 usually with one or two small accessory cusps (the posterior accessory cusp is more consistently distinct than the anterior cusp); P1 present, smaller than posterior premolars but not vestigial; P2 distinctly shorter than P3; P3 without anterior cutting edge; upper molars strongly dilambdodont and highly carnassialized, increasing in width (transverse dimension) from front to back (width M1 « width M4); ectoflexus shallow or absent on M1, deeper on M2, and consistently deep on M3. Unworn lower incisors with distinct lingual cusp; c1 procumbent, usually with small posterior accessory cusp (often absent on even moderately worn teeth); p2 taller than p3; m3 hypoconid labially salient (level with labial apex of protoconid); hypoconulid twinned with entoconid; entoconid large, much taller than hypoconulid.

COMPARISONS WITH GRACILINANUS : Species of Cryptonanus and Gracilinanus are similar in size and external characters and might be indistinguishable in the field. 4 Although sideby­side comparisons of museum specimens suggest that species of Gracilinanus tend to have broader circumocular masks, larger ears, and longer mystacial vibrissae than species of Cryptonanus , these impressions are hard to document with measurements or illustrations. Species of Gracilinanus also appear to have relatively longer tails (on average) than species of Cryptonanus , but there is enough overlap in the data at hand (table 2) to suggest that this trait is not a reliable basis for generic identifications.

Visual cranial comparisons (figs. 1, 2) suggest that Cryptonanus specimens have relatively shorter rostrums and smaller orbits than specimens of Gracilinanus , but such proportions are ontogenetically variable and available samples are too small for statistically compelling morphometric analyses. Fortunately, several discrete characters provide a less subjective basis for taxonomic diagnosis (table 3). A secondary foramen ovale (formed by an anteromedial process of the alisphenoid tympanic wing; Voss and Jansa, 2003: character 45, fig. 8) is uniformly present in our material of five species of Gracilinanus , including G. aceramarcae , G. dryas , G. emiliae , G. marica , and G. microtarsus . By contrast, a secondary foramen ovale is consistently absent in examined specimens of Cryptonanus chacoensis , C. guahybae , C. ignitus , and C. unduaviensis .

4 Three species of Cryptonanus that usually have selfwhitish or self­buffy ventral fur ( C. agricolai , C. chacoensis , and C. unduaviensis ) occur sympatrically with Gracilinanus agilis , which usually has distinctly graybased ventral fur. Allopatric congeners, however, are differently marked. Cryptonanus guahybae , for example, has gray­based ventral fur, and some species of Gracilinanus (e.g., G. emiliae ) have self­whitish ventral fur.

TABLE 2 Relative Tail Length (LT/HBL) among Species of Gracilinanus and Cryptonanus

Polymorphisms were observed in only two species. Of 38 specimens of G. agilis scored for this character, a secondary foramen ovale was observed in 37 specimens; the unique exception is UMMZ 126104 (from the Paraguayan department of Cordillera), a typical specimen of G. agilis in all respects but its lack of anteromedial bullar processes. The other polymorphic species is C. agricolai , of which two examined adult specimens ( ZMUC 151 , 154 ) have a secondary foramen ovale and six others ( BMNH 93.4.16.4; MN 1494, 36305, 36215; ZMUC 152 , 160 ) do not; a single juvenile (MN 36526, not scored for table 3) also exhibits a secondary foramen ovale, and one adult with damaged bullae ( MN 36216 , likewise not scored) has broken anteromedial processes on each bulla that may have formed a secondary foramen ovale in life .

Maxillary fenestrae (nonvascular perforations of the maxillary palate between the maxillopalatine fenestrae and M1 or M2; Voss and Jansa, 2003: character 40, fig. 5) appear to be consistently present in most species of Gracilinanus (e.g., G. aceramarcae , G. agilis , G. dryas , G. marica , and G. microtarsus ), but they are small and individually variable—sometimes absent unilaterally or bilaterally—in G. emiliae . By contrast, these openings are uniformly absent in our material of three Cryptonanus species ( C. chacoensis , C. guahybae , and C. ignitus ), and they are absent in most examined specimens of two others ( C. agricolai and C. unduaviensis ). The exceptions include the paratype of C. agricolai (MNRJ 1494) , which has a small (0.5 mm) maxillary vacuity on each side of the palate opposite M1; the paratype of C. unduaviensis (AMNH 72565), which has a somewhat larger opening on the right side of the palate; and another specimen of C. unduaviensis (AMNH 209156), which has very small (, 0.5 mm) openings on both sides of the palate.

The relative heights of the second and third upper premolars (fig. 4) provide the most consistent basis for generic diagnosis because intraspecific variation is minimal. However, relative premolar heights cannot be scored from old adults with heavily worn teeth, so sample sizes tend to be smaller for this character than for the two previously discussed. Nevertheless, in all examined specimens of Gracilinanus that preserve the apices of these teeth, P2 and P3 are subequal in height (in most species, P2 and P3 are equally tall, but P2 is often slightly taller than P 3 in our samples of G. aceramarcae , G. emiliae , and G. microtarsus ). By contrast, P2 is distinctly shorter than P 3 in all examined specimens of Cryptonanus with suitably preserved (unworn or lightly worn) dentitions.

A character whose diagnostic potential we did not recognize until late in this project, and for which we have correspondingly less information, is the rostral process of the premaxillae ( Voss and Jansa, 2003: character 29, fig. 4). This bony projection, which extends the suture between left and right premaxillae anterior to I1, is sometimes damaged during specimen preparation, and it is often obscured by dried skin or connective tissue on incompletely cleaned skulls. Among the specimens that we were able to score for this feature (table 3), a rostral process was consistently present in Gracilinanus aceramar­

TABLE 3 Craniodental Trait Frequencies in Species of Gracilinanus and Cryptonanus a cae, G. agilis , G. dryas , G. emiliae , G. marica , and G. microtarsus . 5 No distinct rostral process was observed in Cryptonanus chacoensis , C. guahybae , C. ignitus , or C. unduaviensis . The expression of this character remains to be determined in C. agricolai , ex­

5 We note that there are some taxonomic differences in the expression of this character in Gracilinanus , with G. aceramarcae having the longest rostral processes and G. agilis the shortest among the congeneric taxa we examined.

amples of which are not at hand at the time of writing.

The only other character that merits discussion in this context is the presence or absence of accessory cusps on the upper canine (fig. 3). As previously noted by Voss and Jansa (2003: character 53), this trait must be scored from unworn dentitions because accessory cusps are often absent in old adults of species that consistently exhibit such structures in youth, and because a false pos­

Marmosa agilis agilis: Tate, 1933: 195 (part). Another misidentification based on the same series of ZMUC specimens; not agilis Burmeister, 1854 , a valid species of Gracilinanus .

Marmosa agricolai Moojen, 1943: 2 . Original description based on the holotype (by original designation: MNRJ 1495 ) and one paratype, both collected at Crato , Ceara´, Brazil.

Marmosa (Thylamys) agricolai: Cabrera, 1958: 28 . New name combination.

Thylamys agricolai: Reig et al., 1985: 340 . New name combination implied by raising Thylamys (sensu Kirsch and Calaby, 1977) to generic rank.

Gracilinanus emiliae: Gardner and Creighton, 1989: 6 (part). New generic assignment and synonymy, based on alleged conspecificity with G. emiliae (Thomas, 1909) .

terior accessory cusp is sometimes formed when C1 is notched by occlusion with p1. Based on our examination of specimens with minimally worn dentitions, the upper canine is usually a simple (unicuspid) tooth in most species of Gracilinanus , whereas one or two distinct accessory cusps are usually present in species of Cryptonanus (table 3). The most conspicuous exception to this taxonomic trend is G. emiliae (see Voss et al., 2001: fig. 12), in which a distinct posterior accessory cusp is invariably present.

OTHER COMPARISONS: Morphological comparisons with other didelphid genera that appear to be closely related to Cryptonanus and Gracilinanus are summarized in table 4.

ETYMOLOGY: From the Greek words kruptos (hidden) and nanos (dwarf), as appropriate for small animals whose taxonomic identity has long been concealed by synonymy.

Figures

Fig. 1. Dorsal and ventral cranial views of Cryptonanus unduaviensis (A, B, AMNH 209152) and Gracilinanus agilis (C, D, MVZ 197437) illustrating generic differences discussed in the text.

Fig. 2. Lateral cranial and mandibular views of Cryptonanus unduaviensis (A, AMNH 209152) and Gracilinanus agilis (B, MVZ 197437) illustrating generic differences discussed in the text.

Fig. 3. Labial views of C1–P3 in Cryptonanus chacoensis (A, UMMZ 126105) and Gracilinanus agilis (B, UMMZ 134005) illustrating generic differences in the occurrence of accessory canine cusps and in the relative heights of P2 versus P3 (see text).