Myotis riparius Handley, 1960

Novaes, Roberto Leonan M., Claudio, Vinicius C., Diaz, M. Monica, Wilson, Don E., Weksler, Marcelo & Moratelli, Ricardo, 2022, Argentinean Myotis (Chiroptera, Vespertilionidae), including the description of a new species from the Yungas, Vertebrate Zoology 72, pp. 1187-1216 : 1187

Myotis riparius Handley, 1960

Comments.

Small to medium-sized species (FA 33.4-36.3 mm, body mass 4-5 g; Table 7 ; Fig. 14 ), with wooly, moderately long fur (LDF 6.5-7.5 mm, LVF 5.5-7.0 mm). Ears comparatively short (length 12-15 mm). Most individuals have dorsal fur subtly bicolored, with Bone Brown bases (2/3 hair length) and tips (1/3 hair length) ranging from Cinnamon-Brown to Snuff Brown, with a burnished aspect (e.g., CML 3155). However, some specimens have unicolored dorsal fur generally Cinnamon-Brown (e.g., CML 5412). Ventral fur strongly bicolored, with Clove Brown bases (2/3 hair length) and generally Deep Olive Buff tips (1/3 hair length). Membranes and ears are Mummy Brown. Legs and dorsal surface of uropatagium naked. Lack of a fringe of hairs along the trailing edge of the uropatagium. Plagiopatagium attached to feet on the level of the base of the toes by a wide band of membrane. Skull moderate in size (GLS 13.3-13.8 mm, BCB 6.3-6.4 mm), and the rostrum comparatively short and broad. The P3 is smaller than P2 and can be aligned in the toothrow or displaced to lingual side, but always visible in labial view. Sagittal crest present, ranging from low to medium; lambdoidal crests present and ranging from low to medium. Parietals decay anteriorly; occipital region is almost flattened, but projects beyond the occipital condyle limits; braincase elongated in dorsal view; postorbital and interorbital constrictions comparatively wide.

Myotis riparius occurs from Honduras, southward through South America into northern Argentina and eastern Brazil, occupying humid tropical forests to savanna environments ( Novaes et al. 2017; Moratelli et al. 2019a). Myotis riparius has a marked geographic variation in relation to fur coloration and skull features, which has raised suspicions that this species is, in fact, a cryptic taxonomic complex ( Novaes et al. 2017). Most specimens from Argentina have morphological features that are subtly distinct from those from Panama (including the type series) and northern South America, such as bicolored dorsal fur, skull with lower sagittal and lambdoid crests, and smaller skull and external size. On the other hand, a few specimens have fur color and cranial traits more similar to the forms from Central America and northern South America. We do not reject the hypothesis that Argentinean populations currently under the name Myotis riparius might be a distinct species; it is also not impossible that populations of M. riparius from Argentina may be hiding two sympatric cryptic species. However, more investigations are needed to understand the taxonomic status of the Argentinean populations currently named as M. riparius , and molecular data are needed to understand whether these patterns of variation represent independent evolutionary lineages.

In Argentina, M. riparius occurs in the northern portion, from Southern Andean Yungas (Jujuy, Salta, and Tucumán Provinces) throughout ombrophilous tropical forests in Humid Chaco (Province of Chaco and Formosa), Dry Chaco (Santiago del Estero), and moist Atlantic Forest (Misiones Province), in an altitudinal range from 70 to 2,000 m ( Barquez and Díaz 2020). It is possible that records of M. riparius from the Pampa and Espinal ecoregions, in the provinces of Buenos Aires, Corrientes, and Entre Ríos, may represent the newly described Myotis pampa Novaes, Wilson & Moratelli, 2021. Therefore, specimens that resemble M. riparius from these regions need to be revised.

Figures

Figure 14. Adult female of Myotis riparius (MACN 20906) from Formosa, Argentina.