Leiuromys occasius ( Thomas, 1921 )

Emmons, Louise H. & Fabre, Pierre-henri, 2018, A Review of the Pattonomys / Toromys Clade (Rodentia: Echimyidae), with Descriptions of a New Toromys Species and a New Genus, American Museum Novitates 2018 (3894), pp. 1-52 : 25-27

Leiuromys occasius ( Thomas, 1921)

Echimys occasius Thomas, 1921: 450 (original description).

Echimys armatus occasius: Ellerman, 1940: 112 (name combination).

Makalata occasius: Emmons and Feer, 1997: 237 (name combination).

Pattonomys occasius: Emmons, 2005: 282 (name combination).

TYPE SPECIMEN: The holotype, BMNH 21.2.15.6, consisting of the skin and skull of a juvenile female (with M2 unerupted), was collected for Ludovic Söderström (probably by his native employees; see Chapman, 1926) on 20 February 1914, and subsequently acquired by exchange from the Stockholm Museum.

TYPE LOCALITY: Allegedly “Gualea, Ecuador, west of Pichincha. Alt. 4000 [ft]” ( Thomas, 1921: 450). Tate (1935: 435) wrote “(Erroneous?)” next to this locality, and Emmons (2005) likewise surmised this type locality to be erroneous, because Gualea is in the western foothills of the Andes and all other known specimens are from lowland evergreen forests of eastern Ecuador and Peru. Moreover, the microhabitat noted on the skin tag is not plausible. 3 In 1914 Söderström acquired birds from around Pichincha, Gualea, on the western Andean slope, but also a montane hummingbird ( Aglaiocercus kingii ) from Baeza (VertNet records) at 1900 m in the foothills of the eastern Andes. Baeza is only about 30 km from Río Suno Abajo, and 60–70 km from Río Jatunyacu (800 m), both collection localities of L. occasius . A Söderström specimen of a motmot species known from Baeza (now Momotus momotus ) was likewise erroneously labeled as from Gualea ( Chapman, 1926: 273). Therefore, the type locality (defined as the locality where the holotype was actually collected; ICZN, 1999) is almost certainly somewhere in the lowlands of eastern Ecuador.

DIAGNOSIS AND DESCRIPTION: As for genus (above).

HABITAT: All examined specimens except the holotype are from 150 to 800 m in regions of tall, evergreen, humid Amazonian forests within about 300 km of the Andean foothills. All such collection localities are along rivers (the main travel routes when they were collected), and the collectors did not record habitat details. One of us (LHE) in 1982 photographed a Leiuromys , provisionally identified by its bright orange-buff underparts, gray cheeks, naked tail, and white teeth, at Cocha Cashu Biological station in Manu National Park (fig. 1, locality 32). It was in whitewater floodplain forest, sitting motionless crosswise on a wide branch in the under canopy, at about 8–10 m height. No other Echimyini are known from the region of the southern population in the Department of Madre de Dios, Peru ( Emmons et al., 2015a: maps 494–498), where there is a mysterious distribution gap for Makalata and Isothrix , no Echimys , and the only known arboreal Echimyidae are Dactylomys boliviensis and Mesomys hispidus .

REMARKS: The two groups of northern (Ecuadorean) and southern (Peruvian) specimen localities are over 1000 km apart. A sequenced individual from each population ( FMNH 14409 , MCZ 37964) showed a cyt -b sequence divergence of 2% ( table 2), a difference that merits further investigation. Because only three specimens are recorded from southern Peru, and three of the nine specimens that we examined are subadults with unerupted M3, we did not try to

3 “Killed between the stones in a stream” is written on the label, but this was not mentioned by Thomas (1921).

test for morphological variation between the two populations, but specimens from southern Peru seem to have paler underparts, with more self-white areas, than specimens from Ecuador and northern Peru.

SPECIMENS EXAMINED: ECUADOR: Pichincha, Gualea , 4000′ ( BMNH 21.2 .15.6 [holotype]) ; Napo, Río Suno abajo 800 m ( AMNH 68177 ) ; “ Napo ” ( BMNH 34.9.10.202); Río Jatún Yacu (= Jatunyacu ), 750 and 800 m ( MCZ 37964*) . PERU: Loreto, Maynas, Boca Río Curaray ( AMNH 71897 ) ; Boca Río Santiago ( AMNH 98262 ) ; Madre de Dios, Río Colorado , near the mouth ( FMNH 84259 *, 84427) .