Sciurus (Hadrosciurus) pachecoi, Voss & Fleck & Jansa, 2019

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 : 22-26

Sciurus (Hadrosciurus) pachecoi , new species

Figures 5B, 6B, 8C, 10A, 10D, 11A, 13, 15

Hadrosciurus “species 3”: Abreu et al., 2020b: 8 (informal name for an undescribed putative species identified by phylogenetic analysis of mtDNA sequence data).

HOLOTYPE: AMNH 73924, consisting of the skin and skull of an adult female collected at Orosa (on the right bank of the Amazon at or near the mouth of the Río Orosa ; see appendix 1), Loreto department, Peru, by Alfonso and Ramón Olalla on 21 September 1926. The tip of the tail is missing, but the specimen is otherwise intact. A complete mitochondrial genome from this specimen was analyzed by Abreu et al. (2020b), who deposited the sequence in GenBank with accession number OM154952.

OTHER VOUCHER MATERIAL (N = 25): Nuevo San Juan ( AMNH 268251, MUSM 13353), Orosa ( AMNH 73917–73923, 754079–74083), Quebrada Esperanza ( FMNH 88982, 88983), Quebrada Vainilla ( LSUMZ 28416, 28417), San Fernando ( FMNH 88981), Santa Cecilia ( FMNH 87173–87177).

OTHER SPECIMENS EXAMINED: In addition to the 26 specimens from the Yavarí-Ucayali interfluve listed above, we examined three others (AMNH 76443, 75277, 75278) collected just outside our region on the right (“east”) bank of the lower Ucayali. Although these specimens are all labelled “Sarayacu,” documentary evidence summarized by Wiley (2010: 41–43) suggests that they came from two different camps (table 4), one opposite the town of Sarayacu (ca.

6°47′S, 75°07′W) and the other a few kilome- anteromedial wall of the orbit) and the dorsal ters upriver near the modern town of Orellana palatine foramen (in the floor of the orbit) are (ca. 6°55′S, 75°09′W). always separate, but the sphenopalatine vacuities OTHER INTERFLUVIAL RECORDS: 6 Actiamë (in the roof of the mesopterygoid fossa) are ( Amanzo, 2006), Anguila (Escobedo-Torres, highly variable: small or even absent in some 2015), Itia Tëbu ( Amanzo, 2006), Río Yavarí- individuals (e.g., MUSM 13353) but quite large Mirím ( Salovaara et al., 2003), San Pedro (Valqui, in others (e.g., AMNH 73917). The optic fora- 1999, 2001). men is usually larger than the sphenopalatine DISTRIBUTION AND SYMPATRY: Sciurus pache- foramen, and an accessory foramen ovale is coi is only known from the Peruvian department almost always bilaterally present (fig. 6B). Of 18 of Loreto, where it has been collected south of adult specimens that could be scored for contacts the Amazon and east of the Ucayali (fig. 12). In among the alisphenoid, frontal, parietal, and the Yavari-Ucayali interfluve (e.g., at Nuevo San squamosal bones on the lateral surface of the Juan) it occurs sympatrically with Sciurillus braincase, 12 exhibit alisphenoid-parietal conpusillus, S. pyrrhinus , S. spadiceus , and S. flavi- tact, whereas 6 exhibit squamosal-frontal conventer. On the right (“east”) bank of the Ucayali tact. The upper incisors are opisthodont or opposite Sarayacu it additionally occurs with S. orthodont, and there is only a single premolar in ignitus , which it closely resembles in size and each upper cheektooth row (P3 is absent). dorsal coloration (see below). COMPARISONS: Sciurus pachecoi differs con- DESCRIPTION: This is a medium-sized (230– spicuously from three other members of the 280 g) squirrel that is uniformly grizzled brown- subgenus Hadrosciurus — S. igniventris , S. pyrish dorsally from nose to rump (fig. 13), without rhinus, and S. spadiceus —which are all much any markings other than a narrow ring of pale- larger and have reddish or blackish dorsal pelorange fur around each eye. Postauricular age (for additional contrasting traits of sympatpatches of contrastingly pale fur behind the pin- ric S. pyrrhinus and S. spadiceus , see table 2). nae are absent. The tail is lightly frosted with Instead, S. pachecoi closely resembles S. ignitus , orange, but it is not banded or otherwise pat- another species of the Hadrosciurus clade (sensu terned. The ventral pelage is abruptly paler from Abreu et al., 2020b). 7 Sciurus pachecoi and S. chin to anus, including the insides of the fore- ignitus are mostly allopatric, but these species and hind limbs. The predominant ventral color- occur together on the right (“east”) bank of the ation is yellowish orange, paler in some Ucayali just west of our region (table 4, fig. 12). individuals than in others, but at least some of the ventral hairs (especially posteriorly) have 7 Abreu et al.’s (2020b) sequencing results and our examination of relevant type material (see below) are consistent grayish bases. All adult female specimens with with Vivo and Carmignotto’s (2015: 41) hypothesis that the countable mammae (N = 4) have eight teats. following nominal taxa are conspecific: ignitus Gray, 1867 ; The skull (fig. 10A, 10D, 11A) is unremark- irroratus Gray, 1867 ; cuscinus Thomas, 1902; ochrescens Thomas, 1914; iquiriensis Vieira, 1952; boliviensis Osgood, able in gross morphology (resembling those of 1921; argentinius Thomas, 1921; and sanborni Osgood, 1944. many other squirrels of similar size), without However, we not type have examined material of cabrerai unusual rostral, zygomatic, or bullar propor- Moojen, 1958, which might or might not also be a synonym of S. ignitus . By contrast, neither Abreu et al.’s (2020b) results tions. The sphenopalatine foramen (in the examination of representative specimens nor our supports Vivo and Carmignotto’s (2015) hypothesis that any of these taxa are closely related to the species they called Notosciurus 6 All originally reported as Sciurus ignitus . pucheranii (Fitzinger, 1867) . FIG. 13. Dorsal view of skins of squirrels in the subgenus Hadrosciurus . Left to right: Sciurus pachecoi (LSUMZ 28417), S. pyrrhinus (AMNH 73874), a red-phase specimen of S. spadiceus (AMNH 73870), and a black-phase specimen of S. spadiceus (AMNH 73881).

Despite their external similarity, S. pachecoi and S. ignitus are not sister taxa, because each is more closely related to one or more of the larger reddish or blackish species of the Hadrosciurus group (fig. 14).

Like the present species, Sciurus ignitus is a medium-sized, albeit somewhat smaller (ca. 170–240 g) squirrel, with similarly unpatterned, uniformly grizzled-brownish or -olivaceous dorsal fur. However, all the specimens of S. ignitus that we examined have pale (usually orange, but sometimes yellowish or even whitish) postauricular patches. The ventral pelage of S. ignitus is highly variable across the species’ considerable geographic range, but in the Peruvian department of Loreto, S. ignitus has much darker ventral fur than S. pachecoi , especially laterally and on the insides of the fore- and hind limbs (fig. 15). Lastly, parous adult females of ignitus with countable mammae (N = 26) invariably have just six teats.

Sciurus ignitus is very similar to S. pachecoi in cranial morphology but averages slightly smaller in most measured dimensions (table 5). Additionally, the sphenopalatine foramen of S. ignitus is usually equal to or larger than the optic foramen, the foramen ovale accessorius is almost always bilaterally absent (fig. 6A), and the alisphenoid and parietal are almost always in contact on the lateral braincase. Although few of these cranial differences are absolute (table 6), specimens with atypical traits for one character are not atypical in other respects, such that polymorphisms are seldom a problem for specimen identification.

One specimen of Sciurus pachecoi from the Yavarí-Ucayali interfluvium (AMNH 73917) was identified as Guerlinguetus aestuans by Vivo and Carmignotto (2015), who identified two others (FMNH 87173, 88981) as Notosciurus pucheranii . Neither identification is plausible in the context of Abreu et al.’s (2020b) phylogenetic results, but such discrepancies illustrate the still confused taxonomy of Neotropical squirrels and the urgent need for revisionary studies to reconcile molecular results with morphological character variation.

ETYMOLOGY: For Victor Pacheco, curator of mammals at the Museo de Historia Natural de la Universidad Nacional Mayor de San Marcos, whose career accomplishments have substantially transformed Peruvian mammalogy and