Myotis atacamensis (Lataste, 1892)

Novaes, Roberto Leonan M., Pedro, Annia Rodríguez-San, Saldarriaga-Córdoba, Mónica M., Aguilera-Acuña, Omayra, Wilson, Don E. & Moratelli, Ricardo, 2022, Systematic review of Myotis (Chiroptera, Vespertilionidae) from Chile based on molecular, morphological, and bioacoustic data, Zootaxa 5188 (5), pp. 430-452 : 443-444

Myotis atacamensis (Lataste, 1892)

Type. Neotype USNM 391786 , adult female collected by W. Mann and S. Mann in January 1944; skull partially damaged, mandible, and skin (see Novaes et al. 2022b).

Type locality. Near Minimini , Tarapacá, Chile.

Distribution. Occurs from Arequipa, in western Peru, to northern Chile, being associated with Desertic and Xeric Tropical formations in elevations from 990 to 3,475 m, where it inhabits vegetational formations such as Absolute Desert, Desertic Shrubland, and Highland low-Shrublands.

Diagnosis. Small size (FA 30.6–34.1 mm; GLS 12.6–13.6); dorsal fur long (7–9 mm), silky, and tricolored, with dark-brown bases (near Bone Brown), pale yellowish middle portions (near Pale Olive-Buff), and yellowishbrown tips (near Light Ochraceous Buff); ventral fur strongly bicolored, with Bone Brown bases and whitish-gray tips (near Pallid Brownish Drab); dorsal surface of the uropatagium covered by thin fur not extending beyond the knees; presence of a fringe of sparse hairs on the distal border of the uropatagium; plagiopatagium connected to the feet by a broad band of membrane. Sagittal crest usually absent; elongated and narrow skull; braincase remarkably inflated and high in profile; braincase roof formed by the parietal bone is straight; forehead steeply sloping in lateral view; narrow and short rostrum; posterior region of the braincase rounded and quite projected beyond the limit of the occipital condyles; mastoid processes narrow

Description and comparisons. Dental formula is I 2/3, C 1/1, PM 3/3, M 3/3 (2x) = 38, and the teeth are small. Skull small; forehead steeply sloping with inflated braincase; braincase roof is straight; mastoid processes narrow and poorly developed; rostrum narrow and comparatively short; the sagittal crest and lambdoidal crests are usually absent; and the occipital region is rounded and conspicuously projected beyond the posterior surfaces of the occipital condyles. The second upper premolar (P3) is a little smaller than the first upper premolar (P2), aligned in the toothrow and visible labially in all individuals.

Ears are moderate in size, almost reaching the nostrils when extended forward. Membranes and ears are Mummy Brown or lighter. Plagiopatagium is connected to the feet at the level of the toes by a broad band of membrane; a fringe of scattered hairs on the distal border of the uropatagium is present and visible only under magnification. Dorsal surface of the uropatagium barely furred, with hairs not extending beyond to the knees. Silky and long fur; dorsal hairs tricolored, with Bone Brown bases (2/5 of total hair length), Pale Olive-Buff middle portions (2/5 of total hair length), and Light Ochraceous Buff (1/5 of total hair length), however, the contrast between tip and middle portion of the hair is quite subtle. Ventral fur strongly bicolored, with Bone Brown bases (2/3 of total hair length) and Pallid Brownish Drab tips (1/3 of total hair length).

Myotis atacamensis differs from all South American congeners by the tricolored dorsal fur. From Chilean Myotis , M. atacamensis can be distinguished from M. arescens and M. chiloensis by its general smaller size ( Table 3 ); silky, brighter, and longer fur, with dorsal hair tricolored and strongly contrasting between bases (dark brown) and tips (yellowish), and whitish-gray venter; in M. chiloensis , the fur is woolly and shorter, dorsal hairs with weak contrast between bases (medium-brown) and tips (cinnamon-brown) and medium-brown venter; whereas in M. arescens , the fur is woolly and shorter, dorsal hairs with clear contrast between bases (dark-brown) and tips (cinnamon-brown), and pale-yellowish venter.

Myotis atacamensis is morphologically closer to M. bakeri , from which it can be distinguished by slightly lighter dorsal fur (near Light Ochraceous Buff on the tips in atacamensis and near Buckthorn Brown on the tips in bakeri ); presence of a fringe of hairs along the trailing edge of uropatagium (absent in M. bakeri ); and narrower skull (e.g., POB <3.5 in atacamensis, POB ≥ 3.5 in bakeri ); in addition, the base of dorsal fur is dark brown in M. atacamensis and blackish in M. bakeri . From M. albescens , M. atacamensis can be distinguished by the conspicuously paler dorsal fur color (dorsal fur dark to medium-brown on the bases [4/5 of the total fur length] and yellowish on the tips [1/5] in albescens , conveying a brownish general appearance to the dorsum; in contrast with bases and tips strongly contrasting and general yellowish appearance in atacamensis ). Additionally, M. albescens have the throat yellowish, grading to whitish towards the abdomen and perianal area, and a more globular braincase (see Moratelli & Oliveira 2011); whereas in M. atacamensis the entire venter, from the throat to the abdomen, is whitish-gray and the skull is narrower, and the braincase is less globular. In addition, M. atacamensis is conspicuously smaller than M. albescens in external and cranial measurements (see Moratelli & Oliveira 2011).

Myotis atacamensis can be distinguished from M. oxyotus by the dorsal fur paler and with strong contrast between bases and tips, and the ventral fur whitishgray; whereas the dorsal fur is darker, and the ventral fur is yellowish in M. oxyotus . Myotis atacamensis is smaller than M. oxyotus in virtually all external and cranial measurements (e.g., GLS 12.6–13.6 mm in atacamensis , 14.1–15.0 mm in oxyotus ; POB 3.0– 3.2 mm in atacamensis , 3.3–3.9 mm in oxyotus ; MAL 8.5–9.3 mm in atacamensis , 9.9–11.2 mm in oxyotus ). Myotis atacamensis can be distinguished from M. keaysi by its general smaller size (FA 30.6–34.1 mm in atacamensis , 38.5–43.4 mm in keaysi ; GLS 12.6–13.5 mm in atacamensis , 13.9–14.7 mm in keaysi ), paler, longer, and silky fur (shorter, woolly, and either brownish or reddishbrown in keaysi ). In relation to skull morphology, it differs from M. keaysi by sagittal crest usually absent, mastoid process narrower and poorly developed, and shorter rostrum. In addition to these characters, M. atacamensis differs from its aforementioned South American congeners, except M. albescens and M. arescens , by the presence of a fringe of scattered hair on the distal edge of the uropatagium.