Range extension of Oxymycterus wayku ( Mammalia : Rodentia : Cricetidae ) , an endemic species from austral Yungas , and first record for Catamarca province , northwestern Argentina

Oxymycterus wayku Jayat, D’Elía, Pardinãs, Miotti & Ortiz, 2008, a rodent species recently described, is known in only four localities within the Subtropical Mountain Forests of the Yungas eco-region in Tucumán, northwestern Argentina. Specimens were recorded in an owl pellet sample during a recent survey. This record represents the first for Oxymycterus in Catamarca Province, extending approximately 60 km south its southern distribution in the region. Sixteen other small non-volant mammal species were recorded there, turning this area into one of the most diverse for this understudied group in Argentina.

Oxymycterus wayku is restricted to southern Yungas, in Tucumán province, where it has only been recorded at four localities on the humid eastern slopes of Cumbres Calchaquíes and Sierra del Aconquija (Jayat et al. 2008a).This species probably lives only in a narrow belt of humid forest, from about 800 m elevation in Selva Montana (sensu Brown et al. 2001) to the ecotone between Alnus woodland (Bosque Montano; sensu Brown et al. 2001) and highland grasslands, at about 2200 m elevation (Jayat et al. 2008a).This environment extends continuously to neighboring southern Salta province and southern Catamarca province.In this work, we recorded the species for the first time in Catamarca province, extending its southern distribution, and adding the genus Oxymycterus to the mammal fauna of an additional province in Argentina.The studied specimens were recovered from a pellet sample of Tyto alba (Aves, Strigiformes, Tytonidae) collected in December 2013 from a small gully beside the Highway 1, approximately 3 km north of Las Chacritas (27°38ʹ19ʺ S, 065°57ʹ30ʺ W, 2,025 m elevation), Catamarca province, Argentina (Figure 1).The specimens were identified using literature (Jayat et al. 2008a;Ortiz and Jayat 2013)   (JPJ; to be deposited in the MACN) (Appendix 1).The specimens collected are deposited at the CEI collection under the number 102-6.
The studied specimens, corresponding to one fragmented skull and one left hemimandible, were identified as O. wayku based on cranial and mandibular morphology and morphometric values (Figure 2; Table 1).Diagnostic characters of O. wayku such as short incisive foramina, wide and shallow zygomatic notches, and asymmetrical lunar notch in mandible were evident in our specimens.These traits allowed us to clearly distinguish the recovered specimens from O. paramensis, the other species that inhabits the southern Yungas.The examined fragments of skull present wider and shallower zygomatic notches and shorter incisive foramina in comparison with O. paramensis.Furthermore, in CEI 102-6 the sigmoid notch is narrower and shallower and the lunar notch is clearly more asymmetrical, as observed in O. wayku (Jayat et al. 2008a; Ortiz and Jayat 2013) (Figure 2).
The collecting site is situated on the bottom of a small valley, aligned along a north-south axis, that is surrounded by Sierra de Narváez (2,450 m elevation) to the east and a lower range (2,200 m) to the west.Annual mean temperature and precipitation are variable depending on  the location in the valley.The average annual temperature is 15°C, with 1.1°C the average minimum temperature for the coldest month and 29.1°C the average maximum for the warmest month.Annual rainfall varies between 600 and 700 mm and it is concentrated in the summer months (December to March).
The environment around the site corresponds to the highland grasslands of the Yungas Ecoregion (sensu Burkart et al. 1999), characterized by dense grasslands dominated by species of the genera Festuca, Deyeuxia, Chloris, Lamphorothyrsus, Paspalum, Anthaenanthiopsis, and Stipa; and small patches of monospecific alder woodlands (Alnus acuminata) located approximately 1.5 km from the collecting site (Figure 3) (Cabrera 1976, Vervoorst 1982).Nowadays, extensive cattle grazing have modified most of the natural grasslands, which are confined to the steep slopes.
In spite of a relative low number of owl pellets recovered in the site (n = 57), many other species of non-volant small mammals were identified in the whole sample, including the sigmodontines Abrothrix illutea (MNI = 3) (Figure 4).The record of seventeen species in one small owl pellet sample is remarkable and highlights the area of Las Chacritas as one of the localities with the highest diversity of small non-volant mammals in northwestern Argentina (Jayat et al. 2011;Ferro 2013).There are localities in northwestern Argentina with very rich small non-volant mammal communities, such as those from Hualinchay (Tucumán province), where twelve species were registered (Jayat et al. 2008b), or the Las Capillas area (Jujuy province), with fifteen species documented (Ferro 2010).Thus, we think it will be hard to find localities with much higher species richness in the region.
Some of the species recorded in this locality are also remarkable and worth mentioning.For instance, we documented the presence of Reithrodon auritus, a species found in northwestern Argentina in only five isolated localities (in Catamarca and Tucumán provinces) at highland grasslands between 1,950 and 3,000 m elevation (Jayat et al. 2006(Jayat et al. , 2008b)), together with O. wayku in the same area.The record of Cavia tschudii is also noteworthy due to the few known localities for the species in the northwestern region, being the second one for Catamarca province (see Ortiz and Jayat 2012).The high diversity observed in Las Chacritas area is probably a consequence of the environmental complexity and the steep altitudinal gradient (ranging from 2,000 to 2,400 m elevation), with Bosque Montano, high altitudinal grasslands, and semiarid environments coexisting in a relatively reduced area (approximately 25 km 2 ).
Our experience in the area suggests that more species of small non-volant mammals could be present in Las Chacritas.Necromys lasiurus was recorded at 10 km southeastern the collection site (Jayat et al. 2008b) and we expect that at least two species of Thylamys (T.pallidior and T. pulchellus) coexist in the nearby area (Giarla et al. 2010(Giarla et al. , 2014;;Palma et al. 2014).Phyllotis anitae, a species highly associated with Bosque Montano in southern Yungas of Tucumán province (Jayat et al. 2007), could also be present.Despite the fact that the small nonvolant mammals of the Yungas upper belts are among the best studied in northwestern Argentina (Jayat et al. 2007(Jayat et al. , 2008a(Jayat et al. , 2008b(Jayat et al. , 2011;;Ferro and Barquez 2009;Ferro 2013), the records from Las Chacritas indicate how little we know about the diversity and distribution of the group in the region.

Figure 3 .
Figure 3. Panoramic view of the first collection locality of Oxymyxterus wayku in Catamarca Province, Argentina.A: Highland grasslands.B: Small patches of monospecific alder woodlands (Alnus acuminata) of the Yungas Ecoregion.