Myotis arescens Osgood, 1943

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 : 444-445

Myotis arescens Osgood, 1943

Type. Holotype FMNH 24396 , adult male collected by J. A. Wolffsohn on January 1, 1925; skin only.

Type locality. Hacienda Limache , Valparaíso, Chile.

Distribution. There are records from Central Chile, in the regions of Valparaíso, Coquimbo, Maule, and Araucanía, associated with Mediterranean vegetational formations, such as Desertic low-Shrubland, Sclerophyllous Shrublands, Sclerophyllous Forest, and Broadleaf Rainforest, from sea level to 1,020 m a.s.l.

Diagnosis. Medium-sized species (FA 34.5–37.8 mm; GLS 13.6–15.0 mm); dorsal fur medium to long (6.5–7.5 mm), woolly, and remarkably bicolored, with dark-brown bases (near Bone Brown) and tips generally Brussels Brown or Cinnamon Brown; ventral fur strongly bicolored, with Bone Brown bases and Pale Olive Buff tips; dorsal surface of the uropatagium barely furred; fringe of hairs on the distal border of the uropatagium present; plagiopatagium connected to the feet by a broad band of membrane. Sagittal crest usually absent; broader skull; braincase high in profile and elongated in dorsal view; braincase roof formed by the parietal bone is straight; forehead subtly sloping in lateral view; broader 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 robust and well developed. Skull medium to large with braincase elongated in dorsal view; parietals slope subtly forward to frontal bones; braincase roof is straight; mastoid processes narrow and poorly developed; rostrum long and narrow; the sagittal crest absent and lambdoidal crests present and low; and the occipital region is rounded and projected beyond the posterior surfaces of the occipital condyles. The second upper premolar (P3) smaller than first upper premolar (P2), aligned in the toothrow and visible labially.

Ears comparatively large and reach the nostrils when extended forward. Membranes and ears are Mummy 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. Dorsal surface of the uropatagium is barely furred, with hairs reaching knee level or just beyond. Woolly and medium to long fur; dorsal pelage sharply bicolored with Bone Brown bases and tips ranging from Brussels Brown to Cinnamon Brown. Ventral fur strongly bicolored, with Bone Brown bases (1/2 of total hair length) and pale-yellowish tips (near Pale Olive Buff).

Myotis arescens is morphologically closer to M. chiloensis , from which it can be distinguished by lighter ventral fur (near Pale Olive Buff on the tips in arescens and near Dresden Brown in chiloensis ); comparatively longer ears (in chiloensis the ears not reaching the nostrils when extended forward); and narrower rostrum (BAC ≤ 3.6 in arescens, BAC ≥ 3.6 in chiloensis ,). Furthermore, M. arescens is smaller than M. chiloensis in general ( Table 3 ).

Myotis arescens can be distinguished of M. atacamensis and M. bakeri by its general larger size (e.g., FA> 34.5 in arescens, FA <34.5 in atacamensis and bakeri ); woolly fur with cinnamon-brown dorsal hairs, and venter paleyellowish; whereas in M. atacamensis and M. bakeri the fur is silky, dorsal hairs with strong contrast between bases (dark brown or blackish) and tips (yellowish), and venter whitish.

In relation to M. albescens , M. arescens can be distinguished by the conspicuously bicolored dorsal fur, with Bone Brown bases and tips generally Brussels Brown or Cinnamon Brown; whereas in M. albescens the dorsal fur is almost entire Bone Brown with yellowish on the tips (1/5 of hair length). In addition, M. albescens has a more globular braincase (see Moratelli & Oliveira 2011); whereas in M. arescens the braincase is elongated.

Myotis arescens can be distinguished from M. oxyotus by its shorter and woolly fur, with dorsal hairs cinnamonbrown with darker bases, and ventral fur bicolored, with pale-yellowish appearance; whereas in M. oxyotus the fur is silky and very long (LDF> 8 mm), with blackish bases and generally Mummy Brown or Brownish Olive tips, and ventral fur with blackish bases and tips ranging from Pale Pinkish-Buff to Deep Olive-Buff. In M. arescens the parietals slope subtly to frontal bones and braincase is elongated in dorsal view, whereas in M. oxyotus the parietals slope steeply to frontal bones and braincase is inflated in dorsal view. Myotis arescens can be easily distinguished from M. keaysi by its ventral fur color, pale-yellowish in arescens and Ivory Yellow or Light Drab in keaysi ; it differs from M. keaysi by sagittal crest absent, mastoid process narrower and poorly developed, and parietals sloping subtly to frontal bones; in M. keaysi sagittal crest is always present, mastoid process larger and well-developed, and parietals slope steeply to frontal bones. In addition, M. arescens differs from its aforementioned South American congeners, except M. atacamensis , by the long ear, reaching or almost reaching the nostrils when extended forward.