Oligoryzomys microtis ( Allen, 1916 )

Voss, Robert S., Fleck, David W. & Jansa, Sharon A., 2019, Mammalian Diversity And Matses Ethnomammalogy In Amazonian Peru Part 5. Rodents, Bulletin of the American Museum of Natural History 2024 (466), pp. 1-180 : 84-85

Oligoryzomys microtis ( Allen, 1916)

Figures 21C, 21F

VOUCHER MATERIAL (N = 15): Orosa ( AMNH 73833–73846), San Pedro ( UF 30473). Additional material that we have not examined was reported from Jenaro Herrera by Pavlinov (1994) and from El Chino by Valqui (2001).

UNVOUCHERED OBSERVATIONS: None.

IDENTIFICATION: The genus Oligoryzomys (pygmy rice rats or colilargos) includes numerous species of small, soft-furred, long-tailed oryzomyines that collectively range from Mexico to Tierra del Fuego ( Weksler and Bonvicino, 2015b). The western Amazonian species O. microtis , one of the smallest cricetids in our region, 26 has short (5–7 mm) grizzled-tawny dorsal fur and gray-based whitish or buffy ventral fur (except on the chin and in the inguinal region, which have self-colored fur). As in most other congeners, the tail is distinctly bicolored, longer than the combined length of the head and body (see below) and lacks a terminal pencil of distinctively long hairs. The hind foot is narrow, and the middle three digits (II, III, and IV) are much longer than the outermost digits (the claw of dI does not extend to the end of the first phalange of dII, and the claw of dV extends only slightly beyond the first phalange of dIV). Cranial characters (also shared with most other congeners) include the absence of supraorbital beading, deep zygomatic notches, large sphenopalatine vacuities flanking the basisphenoid/presphenoid suture in the roof of the mesopterygoid fossa, absence of an alisphenoid strut, and absence of a supraorbital branch of the stapedial artery (carotid circulatory pattern 2 of Voss, 1988).

Most specimens of Oligoryzomys microtis from the Yavarí-Ucayali interfluve were collected many years ago, lack external measurements, and have hind feet that are too distorted to measure; therefore, only craniodental measurements are available for comparison with the type series (from the north

26 Reliable weight data are unavailable from specimens collected in the Yavarí-Ucayali interfluve, but 10 adults from northern Bolivia (Pando: AMNH 262826–262832, 262837, 262840, 262842) weighed 20 ± 2 g (range: 16–24 g).

Amazonas (MVZ 200908)

Amazonas (MVZ 200928)

Amazonas (MVZ 200927)

Amazonas (MVZ 200909)

Amazonas (MVZ 200907)

Amazonas (MVZ 200910)

Amazonas (MVZ 200912)

(MVZ 200917)

(MVZ 200918) roberti (A) (MVZ 200935)

(MVZ 200947)

(MVZ 200915)

: Amazonas (INPA 4193)

Amazonas (INPA 4207)

: Madre de Dios (KU 144333)

: Madre de Dios (KU 144335)

Madre de Dios (KU 144336)

de Dios (KU 144338)

(MVZ 200934)

17631)

17685) 98797)

44981)

44984) roberti (B) 44982)

44983)

(MVZ 153528)

(MVZ 155005) 16424)

273112) *

15340) *

273119) * roberti (C)

Peru: Loreto (AMNH 276701) *

bank of the Amazon just upstream from Manaus; Voss et al., 2001: 118–119) and with the series collected by Patton et al. (2000) along the Rio Juruá. Homologous sample means (table 28) from these three series are all within a few tenths of a millimeter of one another, suggesting minimal morphometric divergence. Identical karyotypes from specimens collected at Jenaro Herrera ( Sokolov and Malygin, 1994; Aniskin and Volobouev, 1999) and along the Rio Juruá ( Patton et al., 2000), together with the results of sequence-based species delimitation analyses ( Hurtado and D’Elía, 2019), additionally suggest that pygmy rice rats from the Amazonian lowlands of northeastern Peru are correctly associated with western Brazilian populations previously identified as O. microtis . 27

27 By contrast, we are not aware of any karyotypic or molecular data that document the occurrence of this species in eastern Amazonia ( Weksler and Bonvicino, 2015b: map 232).