Thylamys karimii ( Petter, 1968 )

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 : 36-37

Thylamys karimii ( Petter, 1968)

SYNONYMS: None.

DISTRIBUTION: According to Carmignotto and Monfort (2006), who examined much more material than we have seen, Thylamys karimii inhabits open (nonforest) Cerrado and Caatinga landscapes in the Brazilian states of Bahia, Goiás, Mato Grosso, Minas Gerais, Pernambuco, Piauı´, Rondônia, and Tocantins; it has also been collected in the Distrito Federal. Although no Bolivian specimens are known, T. karimii could be expected to occur on the Serranía de Huanchaca in Santa Cruz department, where other Cerrado endemics have recently been discovered ( Emmons et al., 2006). The geographic range of T. karimii overlaps that of T. velutinus (see Carmignotto and Monfort, 2006: fig. 7), but these species have yet to be collected sympatrically.

MORPHOLOGICAL DIAGNOSIS: Body pelage tricolored (abrupt line of transition from darker middorsal to paler lateral coloration present) in all specimens examined by us, but perhaps less distinctly so in other material ( Carmignotto and Monfort, 2006); ventral pelage entirely self-white, usually without lateral zones of gray-based hairs; plantar pads of manus fused together (concave central palmar surface absent) and uniformly covered with small tubercles (plantar dermatoglyphs absent); manual claws long, extending well beyond fleshy apical pads of digits; tail much shorter than combined length of head and body (LT/ HBL X 100 5 77%; N 5 32 [based on measurement data from Carmignotto and Monfort, 2006: table 1]), without pale tip; ventral prehensile surface of tail tip absent. Nasals usually very long (extending posteriorly beyond lacrimals); lacrimal foramina partially exposed to lateral view on orbital margin in most specimens; infraorbital foramen above P3; nasolabial fossa usually shallow (deeply excavated in a few specimens); supraorbital margins beaded; maxillary fenestrae present; crown of second upper incisor (I2) smaller than or subequal to crown of I3; stylar cusp C often present on M1 and M2; metaconule indistinct or absent on M3.

COMPARISONS: Thylamys karimii can be distinguished unambiguously from T. velutinus , the only other member of the subgenus Xerodelphys , by its self-white ventral pelage (the ventral pelage is entirely gray based in velutinus ), and complete lack of plantar dermatoglyphs (vestigial dermatoglyphs are present at the apex of each plantar pad in velutinus ). Cranial character differences are difficult to evaluate with the small samples at hand, but the nasal bones appear to be absolutely longer on average (NL 5 11.6– 13.4 mm; N 5 5) in karimii than in velutinus (LN 5 11.3–11.7 mm; N 5 3) and they usually project posteriorly well behind the lacrimals (the nasals do not extend posteriorly beyond the lacrimals in any examined specimen of velutinus ; table 7). Although we observed supraorbital beads in karimii that we did not see in velutinus, Carmignotto and Monfort (2006) reported beaded interorbitals in specimens of velutinus that we have not examined. Whereas metaconules were indistinct or absent in all three specimens of karimii that we were able to score confidently for this character, distinct metaconules were present in all five scored specimens of velutinus (table 13).

Comparisons of measurement data between larger samples of Thylamys karimii and T. velutinus than we were able to examine are provided in Carmignotto and Monfort’s (2006) exemplary study. Briefly, T. karimii is larger than T. velutinus in most measured dimensions, but it has absolutely and relatively smaller canines, a difference that is conspicuous in side-by-side comparisons. Despite broad overlap in most univariate morphometric comparisons, T. karimii and T. velutinus can be separated into nonoverlapping clusters by canonical discriminant functions analysis ( Carmignotto and Monfort, 2006: fig. 8).

REMARKS: Originally described as a valid species by Petter (1968), karimii was subsequently listed as a synonym of Thylamys pusillus by Gardner (1993), whereas Palma (1995) and Solari (2003) treated it as a synonym of T. velutinus . Carmignotto and Monfort (2006) effectively refuted these synonymies by identifying most of the characters that we now recognize as distinguishing karimii from other species of Thylamys (table 15).

Three specimens of small didelphids collected near Exu in the Brazilian state of Ceará were misidentified as Marmosa karimii by Mares et al. (1981) and Streilein (1982). The single specimen from this series that we examined (CM 80015, from 0.5 km S Exu) is an old adult male Gracilinanus agilis , whereas two others examined by A.P. Carmignotto (in litt., 8 March 2010) are Cryptonanus agricolai : one is MZUSP 16610 (an immature female from Fazenda Guaranı´, 2.9 km N Exu), and the other is MZUSP 16961 (an adult male from Escola Agricola, 0.7 km S Exu). Behavioral observations based on these specimens were erroneously attributed to Thylamys karimii by Creighton and Gardner (2008) despite Palma’s (1995) well-founded doubts about their correct identification.

SPECIMENS EXAMINED (N 5 12): Brazil — Mato Grosso, Chapada dos Guimarães ( ANSP 4632 ), 264 km N Xavantina ( BMNH 76.632 –76.639; USNM 393536–393538 ) .