Myotis atacamensis ( Lataste, 1892 )

Novaes, Roberto Leonan M., LaVal, Richard K., Wilson, Don E. & Moratelli, Ricardo, 2022, Redescription of Myotis atacamensis (Chiroptera: Vespertilionidae) with neotype designation, Zoologia (e 21026) 39, pp. 1-10 : 2-6

Myotis atacamensis ( Lataste, 1892)

Atacama Myotis – vernacular name.

Vespertilio atacamensis Lataste, 1892: 79 .

Myotis chiloensis atacamensis: Miller and Allen, 1928: 192 .

Myotis nigricans nicholsoni Sanborn, 1941: 382 .

Neotype. Adult female ( USNM 391786 ; Figs 1–5 ) collected by W. Mann and S. Mann on January 1944. The skin and skeleton are complete, and skull is partially damaged but in good condition. The neotype is deposited in the National Museum of Natural History, Washington, D.C., USA.

New type-locality. Near Minimini, Tarapacá, Chile (19°10’S, 69°41’W; elevation 1,800 m), inside Atacama desert .

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 yellowish-brown tips (near Light Ochraceous Buff); dorsal surface of the uropatagium covered by dense fur extending just 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 (measurements in Table 1 ); 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 ( Figs 1–3 ). 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 ( Figs 1–3 ).

Ears are moderate in size, but not reaching the nostrils when extended forward. The tragus is elongated, with a broad base and a narrower terminal half; the front edge is almost straight and the tip rounded. Membranes and ears are medium-brown. 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 (although less evident than in M. albescens ). Dorsal surface of the uropatagium barely furred, with hairs not extending beyond to the knees. Silky and long fur; dorsal hairs tricolored, with dark-brown bases (2/5 of total hair length), pale yellowish middle portions (2/5 of total hair length), and yellowish-brown tips (1/5 of total hair length), however, the contrast between tip and middle portion of the hair is quite subtle ( Figs 6, 7 ). 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). The whitish-gray venter contrasts with the yellowish-brown dorsum ( Figs 6, 7 ).

Myotis atacamensis differs from all South American congeners by the tricolored dorsal fur. In addition, considering either the assemblage of Myotis that occurs on the west side of the Andes ( M. albescens , M. bakeri , M. chiloensis , M. diminutus , M. oxyotus , and M. riparius ) or the taxa that occur in mountainous or open environments of the Southern Cone ( M. albescens , M. dinellii , M. keaysi , M. oxyotus , and M. riparius ), it can also be distinguished from all by the set of diagnostic traits reported above. Among them, M. atacamensis is externally closer to M. bakeri , from which it can be distinguished by slightly lighter dorsal fur (near Light Ochraceous Buff on the tips in M. atacamensis and near Buckthorn Brown on the tips in M. 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 M. atacamensis, POB ≥ 3.5 in M. bakeri ; see Moratelli et al. 2019b).

From M. albescens , M. atacamensis can be distinguished by the paler dorsal fur color (dorsal fur medium to dark brown on the bases [4/5 of the total fur length] and yellowish on the tips [1/5] in M. albescens , conveying a brownish general appearance to the dorsum; in contrast with bases and tips strongly contrasting and general yellowish appearance in M. atacamensis ). Additionally, M. albescens have the throat yellowish, grading to whitish towards the abdomen and sides of the body, and a more globular braincase (see Moratelli and 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.

Myotis atacamensis can be distinguished from M. diminutus and M. oxyotus by the dorsal fur paler and with strong contrast between bases and tips, and the ventral fur whitish-gray; whereas the dorsal fur is darker and slightly bicolored, and the ventral fur is yellowish in M. diminutus and 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 M. atacamensis , 14.1–15.0 mm in M. oxyotus ; POB 3.0– 3.2 mm in M. atacamensis , 3.3–3.9 mm in M. oxyotus ; MAL 8.6–9.3 mm in M. atacamensis , 9.9–11.2 mm in M. oxyotus ), and tends to be smaller than M. diminutus in forearm length (FA 30.6–34.1 mm in M. atacamensis ; 33.3–33.4 mm in M. diminutus ), although there is an overlap with larger individuals of M. atacamensis , both in external and in cranial measurements (see Moratelli and Wilson 2011, 2015, Moratelli et al. 2013).

From M. chiloensis , it can be distinguished by the silky, brighter, and longer fur. Myotis atacamensis has dorsal fur with strong contrast between bases (blackish) and tips (yellowish), and whitish-gray venter; whereas in M. chiloensis , the fur is woolly and shorter; dorsal pelage with weak contrast between bases (dark brown) and tips (reddish-brown) and yellowish-brown venter (see Novaes et al. 2018). Beyond the very distinct dorsal and ventral fur colors, M. atacamensis can be distinguished from M. chiloensis by generally smaller size (FA 30.6–34.1 mm in M. atacamensis , 35.5–41.2 mm in M. chiloensis ; GLS 12.6–13.6 mm in M. atacamensis , 13.8–15.3 mm in M. chiloensis ).

In relation to M. dinellii , it can be distinguished by lighter dorsal fur (near Light Ochraceous Buff on the tips in M. atacamensis and from Buckthorn Brown to Dresden Brown on the tips in M. dinellii ) and membranes (almost blackish in M. dinellii ); shorter ears; general smaller size (FA 30.6–34.1 mm in M. atacamensis , 34.4–40.6 mm in M. dinellii ; GLS 12.6–13.6 mm in M. atacamensis , 13.9–15.2 in M. dinellii ); skull higher in lateral view, braincase more globose, and frontals conspicuously steeply sloping.

Myotis atacamensis can be distinguished from M. keaysi and M. riparius by its general smaller size (FA 30.6–34.1 mm in M. atacamensis , 38.5–43.4 mm in M. keaysi , 36.0– 38.4 mm in M. riparius ; GLS 12.6–13.6 mm in M. atacamensis , 13.9–14.7 mm in M. keaysi , 13.3–14.4 mm in M. riparius ), paler, longer, and silky fur (shorter, woolly, and either brownish or reddish-brown in M. keaysi and M. riparius ). In relation to skull morphology, it differs from M. keaysi and M. riparius by sagittal crest absent, mastoid process narrower and poorly developed, and shorter rostrum.

In addition to these characters aforementioned, M. atacamensis differs from all its South American congeners, excepts M. albescens , M. levis (I. Geoffroy, 1824) , and M. dinellii , by the presence of a fringe of scattered hair on the distal edge of the uropatagium.

Distribution. It is known from western Peru to central Chile ( Fig. 8 ). Myotis atacamensis is associated with arid and semiarid formations in elevations from sea level to 3,475 m, where it inhabits xeric vegetational formations, as absolute deserts, desert scrublands, and sclerophyllous forest ( Rodríguez-San Pedro et al. 2014, 2015, 2020, Moratelli et al. 2019a, 2019b).

Figures

Figure 8. Occurrence of Myotis atacamensis, including the new type-locality (red star); records by museum specimens (red circles); and records obtained from the literature (yellow circles – Rodríguez-San Pedro et al. 2014, 2015, 2020).

Figures 1–3. Ventral (1), dorsal (2), and lateral (3) views of the skull, and lateral view of the mandible of the neotype of Myotis atacamensis (USNM 391786) from Atacama Desert, Tarapacá, Chile. Scale bar = 10 mm. Photos by Melissa Hawkins.

Figures 4–5. Dorsal (4) and ventral (5) views of the skin of the neotype of Myotis atacamensis (USNM 391786) from Atacama Desert, Tarapacá, Chile. Photos by Melissa Hawkins.

Figures 6–7. Details of tricolored dorsal fur (6) and bicolored ventral fur (7) of Myotis atacamensis (MVZ 116638).