Thylamys elegans ( Waterhouse, 1839 )

Giarla, T. C., Voss, R. S. & Jansa, S. A., 2010, Species Limits And Phylogenetic Relationships In The Didelphid Marsupial Genus Thylamys Based On Mitochondrial Dna Sequences And Morphology, Bulletin of the American Museum of Natural History 2010 (346), pp. 1-67 : 44-46

Thylamys elegans ( Waterhouse, 1839)

SYNONYMS:? soricinus Philippi, 1894.

DISTRIBUTION: As restricted by authors ( Meynard et al., 2002; Solari, 2003; Braun et al., 2005; Creighton and Gardner, 2008) and as recognized in this report, Thylamys elegans is endemic to central Chile, where its distributional limits remain to be convincingly documented. Examined specimens that we refer to this species were collected between about 30 ° and 36 ° S (in the regions of Coquimbo, Valparaíso, Metropolitana, and Maule), from near sea level to about 1000 m. As noted by Palma (1995), the specimens reported from much lower latitudes and/or higher elevations in northern Chile (Atacama and Tarapacá) by Pine et al. (1979) are referable to T. pallidior . Although Creighton and Gardner (2008: 110) did not map any northern Chilean localities for T. elegans , the elevational range that they attributed to this species (‘‘from sea level to over 3500 m’’) was presumably based on Pine et al.’s (1979) misidentified material. The type of soricinus is said to have been collected near Valdivia (ca. 40 ° S), but no additional specimens have apparently been collected so far to the south ( Palma, 1997).

Although the geographic range of T. elegans is not known to overlap that of any other congeneric species, newly identified material (see Remarks, below) indicates that the the range of T. pallidior closely approaches it in the Coquimbo region, where the two species might eventually be found to occur sympatrically.

MORPHOLOGICAL DIAGNOSIS: Body pelage tricolored (abrupt line of transition from darker middorsal to paler lateral coloration present); ventral pelage narrowly self-whitish or -yellowish from chin to anus, with broad lateral zones of gray-based hairs (in specimens from Coquimbo, Metropolitana, and Valparaíso), or almost entirely gray-based buffy with or without self-whitish midpectoral markings (in specimens from Maule); plantar pads of manus separate, surrounding a concave central palmar surface, and with well developed dermatoglyphs; manual claws long, extending well beyond fleshy apical pads of digits; tail usually longer than combined length of head and body (LT/ HBL X 100 5 108%; N 5 27), without pale tip; prehensile ventral surface of tail tip well developed. Nasal bones usually short (not extending posteriorly as far as the lacrimals); lacrimal foramina usually exposed anterior to orbit or partially exposed on orbital rim; infraorbital foramen above P3/M1 commissure or above M1; nasolabial fossa shallow; supraorbital margins usually rounded or squared; maxillary fenestrae consistently absent; crown of second upper incisor (I2) smaller than or subequal to crown of I3; stylar cusp C almost always absent on M1 and M2; metaconule absent or indistinct on M3.

COMPARISONS: Thylamys elegans can be distinguished unambiguously from T. pallidior by its much broader lateral zones of gray-based ventral fur, which are equal to or wider than the median streak of self-colored fur (versus much narrower than the selfcolored zone in pallidior ). Additionally, the self-colored ventral fur of elegans is usually off-white (‘‘cream’’) or even yellowish, whereas the self-colored ventral fur of pallidior is snowy white. Other characters contribute to the phenotypic distinctness of these species, although none provides a sufficient basis for identification by itself: elegans has, on average, larger hind feet (14–17 mm) than pallidior (12–15 mm), longer manual and pedal digits, shorter nasals (table 7), and less inflated auditory bullae. Digital lengths are difficult to measure (we did not attempt to do so), but the longer fingers and toes of elegans are apparent in most side-by-side comparisons. Bullar size is indexed by the ratio of bullar width to interbullar width (BW/IBW; see fig. 2), a proportion that averages 0.85 ± 0.05 SD (N 5 23) in elegans and 0.98 ± 0.07 SD (N 5 44) in pallidior .

Thylamys elegans externally resembles T. tatei in having wide lateral zones of graybased ventral fur, but these species can be distinguished unambiguously by incisor morphology. Whereas the crown of I2 is consistently smaller than or subequal to the crown of I 3 in elegans , the crown of I2 is consistently larger than the crown of I 3 in tatei ( fig. 17). Additionally, the nasals of elegans are usually shorter than those of tatei (table 7); one or both lacrimal foramina are usually exposed in elegans , whereas both foramina are concealed in tatei (table 8); and the infraorbital foramen of elegans is usually positioned over M1, whereas the foramen is often over P 3 in tatei (table 9). Among the integumental differences that Solari (2003) observed between elegans and tatei , the usual presence of a pale tail tip in tatei and its absence in elegans is the most consistently useful; we did not observe conspicuous differences between these taxa in fur length (10–12 mm middorsally in most examined specimens of both species), dorsal pelage pigmentation, or facial markings.

REMARKS: The holotype of coquimbensis (FMNH 22302), a taxon originally described from the Coquimbo region of Chile as a subspecies of elegans by Tate (1931), is unambiguously referable to Thylamys pallidior . All of the distinctive traits of coquimbensis mentioned by Tate (1931, 1933)— including its pale dorsal coloration, mostly white ventral fur, small feet, and large bullae—are consistent with the diagnostic traits that we attribute to T. pallidior . Sideby-side comparisons of FMNH 22302 with examples of typical T. elegans (which also occurs in Coquimbo; e.g., FMNH 119487) are

TABLE 19 Measurements (mm) of Sequenced Adult Specimens of Thylamys elegans

likewise consistent with the suite of differences that distinguish these species (see Comparisons, above). The occurrence of both species in Coquimbo suggests that they may occur sympatrically there, perhaps somewhere in between Paiguano (30 ° 01 9 S, 70 ° 32 9 W; the type locality of coquimbensis) and Parque Nacional Fray Jorge (30 ° 30 9 S, 71 ° 30 9 W; our northernmost record of T. elegans ) .

We have not examined the type of soricinus, whose widely assumed synonymy with elegans still needs to be confirmed. The type of soricinus, a mounted skin with the skull inside, was last seen by Osgood (1943), who noted that it differed from typical elegans by lacking the continuous median streak of self-whitish fur seen in the latter form; instead, he described the ventral surface of the type of soricinus as entirely covered by gray-based buffy hairs. The only Chilean specimens we examined that fit this description are a small series from Maule (USNM 541587–541591) from which, unfortunately, we have no sequence data. Pine et al. (1979) previously examined this series and concluded that it represents the soricinus phenotype. We agree, but because the Maule specimens are indistinguishable from typical elegans in measurements and qualitative craniodental traits, no taxonomic distinction seems warranted at this time.

Measurements of sequenced adult specimens of Thylamys elegans are provided in table 19.

SPECIMENS EXAMINED (N 5 29): Chile — Coquimbo, 10 km N Puente Los Molles (FMNH 119487), Fray Jorge National Park (MSB 70588, 87095, 87096, 87097); Maule, confluence of Río Maule and Río Claro (USNM 541587), Siete Tasas (USNM 541588–541591); Metropolitana, 7 road km SW Camino Rinconada (UWBM 49000, 49006, 49007, 49011, 49014), 12 road km SW Camino Rinconada (UWBM 44443– 44446), Fundo El Pangue (UWBM 49059), Rinconada de Maipu (MSB 133097), San Carlos de Apoquindo (MSB 133104); Valparaíso, Las Hijuelas (AMNH 97752, 97753), Olmué (AMNH 97755), Palmas de Ocoa (MSB 87098), Papudo (AMNH 97754), Quebrada del Tigre (MSB 133095).