Sciurus, Linnaeus, 1758

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 : 34-35

Sciurus (“ Microsciurus ”) flaviventer ( Gray, 1867)

Figures 8D, 16

VOUCHER MATERIAL (N = 28): Boca Río Yaquerana (FMNH 88991–88893), Nuevo San Juan (AMNH 268250, 272819; MUSM 11188, 13307), Orosa (AMNH 73899–73912, 74074– 74078), Quebrada Esperanza (FMNH 88994), San Fernando (FMNH 88990).

10 “Dorso et lateribus spadiceo nigroq. variis, capite superne obscuriore, abdomine albido, cauda nigro ferruginea, pilis nigris, apice ferrugineis.” (Back and sides grizzled with brown and black, head rather dark on top, abdomen white, tail rusty black, the hairs black at their bases with rusty tips.)

UNVOUCHERED OBSERVATIONS: Actiamë ( Amanzo, 2006), Anguila ( Escobedo-Torres, 2015), Choncó ( Amanzo, 2006), Divisor ( Jorge and Velazco, 2006), Quebrada Pobreza ( Escobedo-Torres, 2015), San Pedro ( Valqui, 1999, 2001), Tapiche ( Jorge and Velazco, 2006), Wiswincho ( Escobedo-Torres, 2015).

IDENTIFICATION: The species referred to Microsciurus by Vivo and Carmignotto (2015) do not comprise a monophyletic group according to phylogenetic analyses of mitogenomes reported by Abreu et al. (2020b). Instead, these diminutive, small-eared, six-mammate sciurines with procumbent upper incisors and two upper premolars appear to belong to three separate lineages: (1) a pair of species (including the type species, alfari J.A. Allen, 1895 , and an unnamed taxon [“species 1”]) restricted to Central America and western Colombia; (2) several species from Central America and the northern Andes (including boquetensis Nelson, 1903; isthmius Nelson, 1899; mimulus Thomas, 1898; otinus Thomas, 1901; and similis Nelson, 1899); and (3) three species from western Amazonia and the eastern Andes (including flaviventer Gray, 1867 ; sabanillae Anthony, 1922 ; and another unnamed taxon [“species 2”]). Each of these three clades is more closely related to larger squirrels traditionally referred to Sciurus , or to other sciurine genera, suggesting that the phenotype traditionally associated with Microsciurus has independently evolved several times ( Abreu et al., 2020b).

Sciurus flaviventer is a widespread western Amazonian species. According to Vivo and Carmignotto (2015: map 8), this squirrel occurs in southeastern Colombia, eastern Ecuador, eastern Peru, and western Brazil. Mitogenomic sequences amplified from specimens identified as S. flaviventer within the geographic range mapped by Vivo and Carmignotto (2015) belong to two strongly supported haplogroups that occupy opposite sides of the Amazon, but these haplogroups are not known to be morphologically distinguishable, and species delimitation analyses suggest that they are conspecific ( Abreu et al., 2020b). Unfortunately, the holotype of S. flaviventer (BMNH 51.7.3.6) is a carelessly labelled Castlenau specimen from “ Brazil,” so it is not known whether this name properly applies to the northern or the southern haplogroup. 11 However, the type is morphometrically similar to our small series from the Yavarí-Ucayali interfluve (table 8), which it also resembles in other phenotypic traits. We have not attempted to assess the taxonomic status of the nominal taxa that Vivo and Carmignotto (2015) regarded as junior synonyms of S. flaviventer , none of which are from localities in or near our region.

In the Yavarí-Ucayali interfluve, Sciurus flaviventer is a small squirrel with very short (6–7 mm), uniformly grizzled-brownish or -olivaceous dorsal pelage. Most specimens have gray-based orange ventral fur, but some (e.g., AMNH 73900, 73903) have paler (gray-based buffy) fur on the chest or throat. The postauricular patches are pale buff or grayish, and the feet do not contrast in color with the dorsal body fur. The tail base is short furred and grizzled brownish like the rump, but the distal caudal fur appears frosted because the longer hairs have pale (buffy or grayish) tips. All examined parous female voucher specimens with countable mammae (N = 4) have six teats. Most adult specimens from our region are unaccompanied by external measurements, but AMNH 272819 measured 145 mm (HBL) × 130 mm (LT) × 41 mm (HF) × 18 mm (Ear), and weighed 100 g. Measurements of undistorted dried hind feet that we obtained from another six specimens ranged from 38 to 42 mm.

Skulls of this species lack a sagittal crest, the squamosal and frontal are in contact on the lateral braincase, and an accessory oval foramen is usually absent (three specimens that we examined exhibit this opening unilaterally). The sphenopalatine and dorsal palatine foramina are separate, and sphenopalatine vacuities in the roof of the mesopterygoid fossa are very small or absent. The upper incisors are conspicuously

11 François-Louis Laporte, comte de Castelnau, was a French naturalist whose travels in Brazil from 1843 to 1847 included a descent of the Amazon with abundant opportunities for collecting on both banks of the river ( Papavero, 1971).