Third time’s the charm: The definitive rediscovery of Telmatobius halli Noble, 1938 (Anura, Telmatobiidae) at its historic type locality

Telmatobius halli Noble, 1938 was the first representative of its genus to be described for Chile, but for 80 years no new individuals could be located due to the vagueness with which its type locality was described. The type series was collected by one of the members of the International High Altitude Expedition to Chile (IHAEC) that took place in 1935. Recently, three studies successively claimed to have rediscovered the type locality in different places. The third study proved, considering the chronicles of the IHAEC, that the actual locality is Miño, at the origin of the Loa River. In the contemporary herpetological literature, there are no records of Telmatobius from this locality. In this study, we provide additional documentary antecedents and graphic material that corroborate that the mentioned location is indeed the historic type locality of T. halli. Additionally, we describe the recently discovered Telmatobius population from Miño, whose external characteristics are consistent with the description of T. halli, and the environment it inhabits. Furthermore, we performed a molecular phylogenetic analysis that strongly suggests that T. halli (from Miño), T. dankoi and T. vilamensis, all known only from their type locality in Chile, are conspecific. Neither of the populations from the previously proposed rediscoveries grouped with the one from the genuine type locality. We discuss the implications that these findings have for the taxonomy, biogeography and conservation of the populations from the extreme south of the distribution of the genus in Chile.


Introduction
The genus Telmatobius Wiegmann, 1834 is one of the few anuran taxa that has managed to diversify in the high Andes (Barrionuevo 2017), so its representatives exhibit a series of physical and physiological adaptions that allow them to survive in such harsh climatic environments (e.g. Ruiz et al. 1983;Reider et al. 2020). In fact, it includes one of the highest-dwelling frog species, Telmatobius marmoratus (Duméril and Bibron, 1841), which has been reported from up to 5,400 m (Reider et al. 2020). Currently, there are 63 recognized species in this genus (Frost 2021), which distribute throughout a variety of ecosystems alongside the Andes, between approximately 1°S and 30°S (Barrionuevo 2017). The biogeographical consequences of the uplifting of the Andes during the late Pliocene and Pleistocene and paleoclimatic processes, such as the repeated formation and evaporation of extensive lakes, have been proposed to be responsible for the diversification of the fauna in the Puna highlands, the driest section of the Central Andes (e.g. Collado et al. 2011;Vila et al. 2013;Sáez et al. 2014). Thus, vicariance seems to be a reasonable explanation for the divergence of the Telmatobius from this arid region, taking into account their strongly aquatic habits (Barrionuevo 2017) and the hostile environments that have evolved around the watercourses.
In Chile, nine species of Telmatobius (seven of them endemic) are currently recognized Correa 2019), although Sáez et al. (2014)
Undoubtedly, a greater sampling effort will bring up even more discoveries, yet the accessibility and the conditions for fieldwork in the region are challenging.
Like in the case of other Chilean amphibian genera (Alsodes Bell, 1843; Eupsophus Fitzinger, 1843) (Blotto et al. 2013;Correa and Durán 2019), the taxonomy of the genus Telmatobius is complex, due to high levels of intrapopulation and interpopulation variation in morphological features (e.g . Trueb 1979;Wiens 1993;De la Riva et al. 2005;Barrionuevo 2017), especially in characters that have been used for diagnosis in the description of some species (De la Riva et al. 2005). Thus, molecular studies have played an important role in the systematics of this taxonomic group in Chile during the past few years (Sáez et al. 2014;Victoriano et al. 2015;Fibla et al. 2017Fibla et al. , 2018 Sáez and Méndez 2020). Nonetheless, a clear species delimitation has not been accomplished yet, and surely a more integrative approach (e.g. Padial et al. 2010) is required to solve the taxonomic problems mentioned above.
Among the endemic species of Chile, Telmatobius halli Noble 1938 stands out for its complex taxonomic history. Dr Frank Gregory Hall collected the type series (adults and larvae) in the context of the International High Altitude Expedition to Chile (IHAEC), an endeavor that took place in 1935 and whose principal purpose was to study the effects of low-oxygen environments of high elevation on the human physiology and the body's acclimatization response (Keys 1936b). Three years after the expedition, Dr Gladwyn Kingsley Noble, from the American Museum of Natural History, described the specimens he had received from Hall and named the species after its collector. There has been considerable confusion regarding T. halli and most part of it must be ascribed to Noble's vague definition of the type locality as "Warm spring near Ollagüe, Chile, 10,000 ft. altitude" (Correa 2021).
Throughout the years, a few populations had been assumed to belong to T. halli (Capurro 1954(Capurro , 1955Cei 1962Cei , 1986Veloso et al. 1982;Northland et al. 1990;Núñez and Gálvez 2015), but were later revised and described as new species (T. dankoi, Formas et al. 1999;T. vilamensis, Formas et al. 2003) or assigned to another taxon, like in the case of the populations from Ascotán Salt Flat, treated as T. cf. philippii by Lobos et al. (2018) (Fig. 1). Furthermore, anurans found at Tatio, San Pedro de Atacama were described as the subspecies T. halli edentatus (Capurro 1955), but Cei (1962) identified the specimens in question as Rhinella spinulosa (Wiegmann, 1834). Formas et al. (2003) redescribed T. halli based on the type material from the American Museum of Natural History (AMNH) and differentiated it from T. dankoi and T. vilamensis using morphological evidence. Over the last three decades, significant efforts have been made to locate the type locality of T. halli (Formas et al. 2003(Formas et al. , 2005IUCN 2015). These expeditions were infructuous in terms of clarifying the whereabouts of T. halli, but led to the description of new species (Telmatobius philippii, Cuevas and Formas 2002;T. fronteriensis, Benavides et al. 2002) and the discovery of a series of undetermined populations (Telmatobius sp. from Ascotán and Carcote salt flats; Sáez et al. 2014) in the area surrounding Ollagüe (Fig. 1).
Previously, a Carcote population (coordinates not specified) was considered as Telmatobius sp. by Sáez et al. (2014) or T. cf. philippii by Lobos et al. (2018). According to the molecular phylogenetic analysis of Sáez et al. (2014), the only one where all of these populations were included, they are nested in different cladesthe T. pefauri (former T. zapahuirensis, see Fibla et al. 2017) and T. hintoni species groups (not recovered in the most recent analysis by Barrionuevo 2017)respectively, so they clearly do not correspond to the same taxon. Nevertheless, the opposing hypotheses of  and Cuevas et al. (2020) were refuted by Correa (2021), who demonstrated, also using bibliographic sources, that the frog was first found near a warm swimming pool in Miño, a location at the source of Loa River, at the western foot of Miño Volcano (Fig. 1C). In the literature, there are no other reports of Telmatobius populations neither from Miño nor from the upper Loa basin.
Altogether, 83 years after its description and despite the multiple recent hypotheses about the location of its type locality and identity, T. halli is still a lost frog and no specimens have ever been seen since the collection of the type series (Correa 2021). So, the main goal of this contribution is to describe the Telmatobius population found in Miño, the place recently identified as the true type locality of T. halli (Correa 2021). We provide a general description of the location, some observations on adults and tadpoles and basic information on the quality of their habitat. Furthermore, we performed a phylogenetic analysis to shed light on the systematic relationships among the population of Miño, the ones recently   Table 1 according to their numeration on the map. Light grey area = Chilean territory, dark grey area = Bolivian territory, grey lines = limits of the sub-basins, blue line = Loa River, red star = study site (Miño), brown marks =   Elevations are expressed in m a.s.l. Note that the specific names assigned to Copaquire, Quebrada Chijlla, Quebrada Choja and Aguas Calientes populations correspond to the taxonomy prior to the proposals of Fibla et al. (2018) and Cuevas et al. (2020).  (Sáez et al. 2014;Fibla et al. 2017Fibla et al. , 2018, but none of them specify the coordinates or a precise site within the salt flat. Only in , the presence of a population of Telmatobius sp. in the Carcote Salt Flat is mentioned, whose coordinates fall very close to the Cuchicha spring (not shown in the map of Fig. 1A), located ~1.9 km NE of Aguas Calientes.

Ecology
We made a general description of the study area, considering the topography of the landscape and more specific conditions at microhabitat level. We measured the stream dimensions at various points and took air and water temperatures at different times of the day. The composition of the adjacent vegetation along the stream was ascertained and a nocturnal survey was undertaken to detect possible sympatric amphibians.
Both, adults and larvae, identified as Telmatobius, were collected during the daytime from the stream using a hand net. The sampling site was about 300 m upstream from the pool identified as the historical place where T. halli was collected (see details in Results). The animals were measured, photographed and finally released back to the capture site. Each individual was handled separately with an unused pair of disposable nitrile gloves (Thomas et al. 2020). To avoid possible toxic effects, the gloves were rinsed and the rinse water was discarded away from the watercourse (Cashins et al. 2008).
In order to obtain bioacoustic data, an AudioMoth recording unit (Hill et al. 2019) was placed beside the stream, at a spot where adult individuals had been sighted during sampling. The device recorded continuously between 8 p.m. and 7 a.m., but we did not obtain vocalizations that could be unquestionably attributed to Telmatobius calls.
In the course of the night, the AudioMoth took a measurement of the air temperature every 15 minutes, but the sensor only has an accuracy of ± 3°C (Open Acoustic Devices 2020). Water temperature was taken with a digital thermometer.

Morphometrics
Seven morphometric features were measured on 11 adult specimens (Watters et al. 2016): snout-vent length (SVL), head width (HW), head length (HL), inter-orbital distance (IOD), inter-nostril distance (IND), foot length (FL) and tibia length (TL). FL and TL were assessed on the right hindlimb. In the case of the tadpoles (n = 9), body length (BL) and total length (TTL) were measured (Altig 2007) and the development stages (Gosner 1960) were determined. All measurements were taken using a vernier caliper to the nearest 0.05 mm.

Sampling and obtaining DNA sequences
Three tadpoles  were anesthetized, immersing them in a buffered solution of MS-222 (0.2%) (Mitchell 2009) and a small portion of the membrane was cut from the caudal fin. After recovery from the anesthesia, they were released at the collection site. The tissue sample was stored in 96% ethanol until DNA extraction. Electropherograms were edited with the program Bioedit v7.1.3 (Hall 1999). Substitution saturation of the sequences was assessed with DAMBE7 (Xia 2018). Sequences were deposited in GenBank (accession numbers pending).

Phylogenetic analysis
The sequences of both fragments were aligned with MUSCLE (Edgar 2004)  bolivianus species group (Sáez et al. 2014;Barrionuevo 2017), which constitutes the sister clade of the three species groups present in Chile (Sáez et al. 2014).

The type locality
Like it is pointed out in Correa (2021), according to the chronicles of the IHAEC by Keys (1936aKeys ( , 1936b and Dill (1979Dill ( , 1980, the collection site of the type series of T. halli was the surroundings of a concrete swimming pool filled with warm water at the source of the Loa River (  As expected, the remains of the mentioned concrete swimming pool were found at 21°12'01"S, 68°40'09"W (3,900 m) (Fig. 3). Even though the stream broke through the lower end of the pool's wall and the bottom is filled with sand, most of the boundaries are still in place and it is evident that the structure corresponds to the one shown in the recording. The pool is rectangular, approximately 6.5 m wide, 20 m long and between 1.5 and 2 m deep. The sidewalls are made of stones, joined together with concrete, while the upper and lower walls are massive concrete blocks. There are other more recent concrete structures inside the stream, one immediately above the pool and another one about 300 m upstream.

Habitat description
The Loa River originates mainly from meltwater from throughout its upper drainage basin, where snow accumulates during austral winter. Several temporal ravines also gather the characteristic precipitations during the austral summer months (December to March), known as Altiplanic winter (Berenguer and Cáceres 2008;Delsouc et al. 2020). Lower down and descending from the east, there also are some important permanent affluents fed by aquifers.
For the first few kilometers, the riverbed is a broad and dry wadi named Miño River. Only about 4 km north of Miño, the arid riverbed gradually turns greener and ends in a small bog with grass tussocks, covering an area of about 5 ha. No significant water flow was registered during this time of the year (late October). At Miño, there are some well-preserved ruins of an old mining camp from the 18 th and 19 th centuries at both sides of the bog (Berenguer and Cáceres 2008), serving as an easily recognizable landmark (Fig. 1C).
From this point on, the river bears the name Loa, as it receives its first permanent tributary, the "Estero Nacimiento" creek (Berenguer and Cáceres 2008 1C).
Below the confluence, the river suddenly turns into a pronounced canyon with vertical cliffs. The concrete pool is located precisely at the beginning of the canyon. Soon after, the river gets a little broader, forming larger natural ponds and sections with rapids. The canyon goes on in a similar manner for almost 100 km, until reaching the Conchi water reservoir. At the pool site, the bottom is also sandy; however, there is a little more mud and detritus, probably coming from the bog and consequently a more abounding aquatic vegetation. The stream at the exit of the pool measures about 4 m in width and 50 cm in depth. Downstream from the pool, the vegetation coverage at the banks decreases a bit, which leaves fewer shelters for the frogs. In fact, a lower population density was detected there.
Adults of T. halli were found mainly under the tussocks, where they shared their refugia with other adults and larvae. On one occasion, 11 adults and one tadpole were captured from below the same plant. Tadpoles also exhibit gregarious habits, but somehow seem to prefer to shelter inside the aquatic vegetation, at the bottom of the stream. Still, they are not absent under the cushions at the riverbank.
Most of the observed larvae were at about the same development stage (Gosner stage 36-37); however, two specimens were younger (Gosner stages 27 and 33). Directly inside the pool, there were very few Telmatobius tadpoles and only one adult was found a few meters below the outlet. At the deepest point of the pool, there was a dead adult of the species.
During the daytime, two adults of Rhinella spinulosa were found under the riparian vegetation in the pool and after nightfall, numerous individuals of these toads were observed outside the water along the stream. A small ravine, adjacent to the pool, was occupied by hundreds of Rhinella larvae in semilentic, shallow puddles, which are ideal for their development. Additionally, one specimen of Pleurodema marmoratum (Duméril and Bibron, 1840) was found walking around at night; hence, all three potential anuran species were present in the area. Since no case of syntopy between the Chilean Telmatobius has been reported, no other congener is expected to be encountered in Miño.

Temperature
In the afternoon (05:00 p.m.), the air temperature was 21.8°C, almost equal to the water temperature at the outlet of the pool (21.4°C). In contrast, in the morning (8:00 a.m.) the air temperature was -2.4°C, while water temperatures at the pool and the sampling site were 19.0°C and 20.7°C, respectively. After sunset, the air temperature dropped quickly to around -11.0°C (00:30 a.m.) and remained alike until dawn. The minimum value was -13.1°C at 03:30 a.m. The water temperature, which is generally higher than that of other localities of the genus (Lobos and Rojas 2020) and which remains more or less constant (19-21.4°C), is consistent with the description of the original capture site ("a warm spring"; Noble 1938).

Morphology
Overall, T. halli is a medium-sized frog (Table 2), with a depressed body, thin forelimbs and anterodorsolaterally orientated eyes (Fig. 5). In dorsal view, the head is slightly broader than long (HL/HW = 0.96), but narrower than the body. On average the head length is 29.65% of SVL. The snout tends to be long but truncated in dorsal view, although it can be rather elliptical in some individuals. In lateral view, the snout profile is quite variable, as it can be flat with a rounded tip or short and acuminate.
Telmatobius halli presents a very smooth skin with minuscule granules, which in some specimens are almost absent on the dorsum. In other cases, they can be more evident on the limbs, flanks, or even covering the ventral surface. Mature males have very small spines associated with the granules, in addition to conspicuous, black nuptial pads on their thumbs. The coloration of dorsum and extremities can be described as a broad spectrum of brown, olive and yellowish speckles that alternate with dark, almost black spots or marks. Some frogs have fewer dark spots and the brown colors predominate, others show extensive dark areas (Fig. 5). The ventral coloration is lighter, with shades of cream or pink, mixed with yellow areas or white dots (Fig. 5E). A noteworthy character is the light, yellow annulus around the eyes of some specimens (Fig. 6), a trait that is shared with T. dankoi and T. vilamensis (von Tschirnhaus, pers. obs.), but not with other Chilean congeners. Loose skin folds at the posterior part of the thighs can be more or less developed, but seem more frequent in corpulent individuals and mature males. Another highly variable character is the extent of the interdigital membrane. All examined animals had fully webbed toes, but while in some cases the webbing was barely distinguishable towards the tips of the phalanges, others presented very prominent lateral fringes. The tadpoles are large and robust (97.27 mm at Gosner stages 36-37) (Table 3), with a thick, pointed tail (Tail length = 1.52x BL; stages 36-37) and show about the same pigmentation patterns as adults, but with entirely smooth skin ( Fig. 5F).  with the maximum support (pp = 1). All the specimens of T. dankoi (n = 4) and T. vilamensis (n = 5) make up a polytomy with two of the tadpoles of T. halli (L2 and L3), which constitutes the sister group of the third tadpole (L1) (Fig. 7). The polytomy results from the fact that the sequences of all these specimens are identical in their entirety (the 1,543 sites of both fragments), while the separation of the tadpole L1 is due to two differences in the cytb fragment.

Discussion
The discovery of a Telmatobius population at the origin of the Loa River (Miño) definitely solves one of the most persistent enigmas of Chilean herpetology: the location of the type locality of T. halli. This riddle persisted for more than eighty years because of the uncritical acceptance of the inherently vague description of the type locality by . However, the solution came from a careful analysis of publications and other documentary sources where some of the members of the IHAEC described their activities and the place and circumstances in which the amphibians were collected (Correa 2021 et al. (2018), some key sources in which the place is explicitly described were not consulted, while in the case of Cuevas et al. (2020), more importance was given to the characteristics of the place they hypothesized as the type locality (Aguas Calientes) than to the information contained in the documentary sources. Cuevas et al. (2020) defined five conditions to validate Aguas Calientes as the type locality of T. halli: "1) the place should be a thermal spring, 2) presence or ruins of a concrete swimming pool in the area, 3) have a small oasis with abundant vegetation, 4) be 3,000 ft (~900 m) down of Collahuasi (Montt) and 5) be located near to Ollagüe." The measurements and observations made here show that Miño fulfills the first four conditions, while the new sources consulted confirm that the fifth one does not apply to T. halli.
The Loa River at Miño has an almost constant water temperature of around 20°C, even at prolonged ambient temperatures below the freezing point, which suggests geothermal activity and matches well with the literature on the type locality of T. halli (Keys 1936a(Keys , 1936bDill 1980). This temperature is similar to that of the collection site in Copaquire (19°C), the purported type locality of T.
halli according to Fibla et al. (2018), but lower than that of Aguas Calientes (27.7°C). Only two other species of Telmatobius are known to inhabit warm or thermal waters, T. fronteriensis in Puquios (originally found in a small thermal pond with a water temperature of 22.9°C, Benavides et al. 2002) and T. cf. philippii in several springs at the Ascotán Salt Flat . In the latter case, the water temperature varies widely between springs and seasons, but in general, spring water has medium to high temperatures compared to the air. In contrast to the water temperature, at Miño we observed a significant fluctuation range between the air temperatures at day and those at night (34.9°C), which could have been even higher, considering that we did not log the temperature data for the entire day.
The constant water temperature may benefit the species, as it serves as a buffer for the thermal oscillations of the environment and prevents thermal stress. Nevertheless, the temperature might not be constant throughout the year, as snowmelt increases the flow rate during thaw season.
We were able to verify on the ground two other conditions defined by Cuevas et al. (2020): the presence of ruins of a concrete swimming pool and an oasis of vegetation. Although Cuevas et al. (2020) (Figs 1C, 2B), suggesting that the vegetation of the place has not changed much since the time of the expedition. The vegetation extends along the riverbed for more than a kilometer upstream from the ruins of the swimming pool and continues downstream along the Loa river canyon, so the place is much more than only a "small oasis" as described by Cuevas et al. (2020).
The elevation of the type locality of T. halli is one of the problematic aspects of the description provided by . Fibla et al. (2018) estimated that the site would be at about 4,000 m a.s.l., considering only the indications given by Dill (1979), while Cuevas et al. (2020) indicated that Aguas Calientes is located at 3,717 m. The altitude of our study site at Miño (3,900 m) was not measured in situ but obtained from Google Earth. Neither of these values matches the one  pointed out in the species description: 10,000 ft (3,048 m). Cuevas et al. (2020) tried to explain this difference by alluding to an underestimation of 610 m in the actual elevation of the Aucanquilcha mine that was reported by members of the expedition (e.g. Keys 1936b;Keys et al. 1938 (Dill 1979(Dill , 1980, although in both cases he indicated that the site where the concrete pool was located was 3,000 ft (~916 m) lower. Ancel Keys instead specified the heights of the pool directly: 3,700 m (Keys 1936a) and 12,000 ft (~3,658 m; Keys 1936b). All these measurements should not be taken as absolute, as they seem a little roughly estimated and were indeed stated in a more anecdotal part of   established that the type locality was at 10,000 ft above sea level, yet it only adds to the general impreciseness of the geographic information in his description.
The fifth condition of Cuevas et al. (2020), the proximity to Ollagüe, is the other problematic aspect of the description of the type locality given by  because there is no place that could be considered close to this town that is at 10,000 ft. In fact, the closest places to Ollagüe with that altitude are about 70 km to the west (in a straight line), on the other side of the Loa River. This is one of the reasons why searches for the species around Ollagüe were unsuccessful (Formas et al. 2003(Formas et al. , 2005IUCN 2015) and why Cuevas et al. (2020) concluded that the type locality is located only 12 km southwest of that town (Fig. 1A), but at a higher altitude. Thus, the suggestion from Fibla et al. (2018) that Noble might have used the location from which the specimens were sent as the type locality seems plausible to us.
In the chronicles of the IHAEC, there is little information about the population of Telmatobius from Miño. Dill (1979Dill ( , 1980 only mentions that Frank G. Hall collected some specimens and that one of them proved to be a new species of amphibian. Keys (1936a) gives more details, indicating that many frogs and tadpoles were found in temperate ponds. This is consistent with the description of the species since the type series consists of five adult females, one immature female and six tadpoles. Currently, there seems to exist an abundant and healthy population, as frogs were found at several spots along the stream. This suggests that the environmental conditions at the site are similar to those at the time of the expedition.
The adults and tadpoles observed in Miño present external characteristics congruent with the description of T. halli . Adults have almost completely smooth skin and a long and flattened snout. In addition, the general coloration, brown and olive with darker irregular spots and the size of the adults and tadpoles is compatible with the type series. Among the internal characteristics, which we did not examine, it is necessary to evaluate in the future the presence or absence of maxillary and premaxillary teeth since it is one of the features that motivated the description of the species. On the other hand, it is necessary to reevaluate the presence of postfemoral folds in the type series. Noble (1938) does not mention anything about this trait in the original description, but Formas et al. (2003), in the redescription of the species, explicitly indicate that it lacks folds. However, in the photographs of the holotype (see fig. 6A in Fibla et al. 2018 andfig. 3E, F in Cuevas et al. 2020) this trait seems to be present. All of the adults that we observed in Miño, both males and females, present postfemoral folds, although they are more developed in males.
This is the first study to include the population that was originally described as T. halli in a phylogenetic analysis. Although this analysis was performed only with mitochondrial sequences (nuclear markers have not yet been included in phylogenetic analyses of the genus), it includes all Chilean species of the genus and all known populations that are geographically close. Telmatobius halli forms a highly supported clade with the two endemic species from the extreme south of the genus distribution in Chile, T. dankoi and T. vilamensis. Furthermore, the sequences (both genes) of two of the three specimens of T. halli are identical to those of these two species. Only one of these two specimens shows two differences in cytochrome b with respect to all the specimens that make up the clade. This result, together with the morphological and biogeographic evidence, strongly suggests that T. halli, T. dankoi and T. vilamensis are conspecific.
The possible synonymy between T. dankoi and T. vilamensis had already been pointed out by Sáez et al. (2014) and reaffirmed by Fabres et al. (2018). These species not only have identical mitochondrial sequences but also have common morphological characteristics that support their close affinity (coloration, size, flattened snout, presence of postfemoral folds, absence of vomers), some of which are also shared with T. halli. The geographic context is also relevant in this case. Telmatobius halli inhabits the same watershed (Loa River) as T. dankoi, while the only known population of T. vilamensis is found in the Salar de Atacama basin, which is southeast of the Loa River basin (Fig. 1A). If in the future, the conspecificity hypothesis receives more support, all these populations should be called T.
halli and we further suggest adopting the vernacular name of T. dankoi (Loa Water Frog), as it has gained popularity and would represent the species appropriately.
The possible conspecificity of these three species also has important consequences for the conservation of these populations due to the current critical situation of T. dankoi and T. vilamensis. In 2019, the only known stream where T. dankoi inhabits almost completely dried up, resulting in the loss of approximately 90% of the total population of the species (Lobos and Rojas 2020). On the other hand, individuals of T. vilamensis have not been observed again in the Vilama River (the only known locality of the species) after a flash flood destroyed the site in 2016 (Lobos and Rojas 2020). Therefore, if these three species are conspecific, Miño would be the only known locality for this taxon with an apparently large population and an unaltered environment. In 2005, the Chilean government started the legal process for the creation of the National Reserve Alto Loa, but the efforts were not carried on and this protected area does not exist yet (Tomás Gerö, CONAF, pers. comm.). Our findings could be an excellent opportunity to resume the task, especially taking into consideration the attention which T.
dankoi received in the international media in 2019 (Lobos and Rojas 2020).
Currently, based on the scarce and incomplete information available for this species, T. halli is listed as Data Deficient by the IUCN (IUCN SSC Amphibian Specialist Group 2015) and as Critically Endangered by the Chilean government (MMA 2019). For this last categorization, in which the uncertainty of the location of the type locality is recognized, it was assumed that the species: has an area of occupancy of about 1 km 2 , is known from a single locality and its habitat is deteriorating due to excessive use of water and the threat of the chytrid fungus (according to observations in other species of the genus in Chile). In this context, the description of the new population of Miño and the environment where it inhabits constitute fundamental information to reassess the conservation status of T. halli, but several aspects must be investigated in greater depth.
Up until now, there seems to exist very little anthropic disturbance at the location described in this work and the place appears to be visited only occasionally by anglers, off-road enthusiasts and mountaineers. Since the times of the IHAEC, it has been a recreational area mainly for the mine staff and, according to locals, still in the 1990s, the spot was sporadically visited by workers from the nearby mines. Accessing the site is very difficult and an increase in tourist activity is unlikely to happen. The valley is very pristine with no visible pollution signs. There is a vehicular track, that crosses the riverbed, which means that there could occur an occasional roadkill or minor contamination with motor oil or fuel; however, given the remoteness of the location not many vehicles pass through. Furthermore, it has yet to be evaluated if the intense nearby mining activity at the Collahuasi and Quebrada Blanca copper mines poses an imminent threat to the Telmatobius population, for instance, if contamination with heavy metals could occur through industrial dust dispersion (e.g. Csavina et al. 2012) or if potential upcoming projects demand water extraction for mining processes.
As mentioned above, other species of Telmatobius have been found infected with Batrachochytrium dendrobatidis (Bd) in northernmost Chile and there is an ongoing spread of chytridiomycosis southwards the Andes (Solís et al. 2015). Now that the type locality of T. halli has been rediscovered, most certainly other herpetologists will visit the place and special attention has to be taken to avoid contamination with the pathogen. Precaution is even more imperative, given the fact that Miño is at the headwaters of the Loa River and Bd could easily expand to other putative populations downstream (Johnson and Speare 2005).
Introduced salmonids are another well-known threat for native amphibians in Chile (Soto-Azat et al.

2015)
. A recent study  reports the presence of Oncorhynchus mykiss (Walbaum, 1792) in several locations of the upper Loa, being Sapunta the nearest sampling point to the source (approx. 18 km). No salmonids were detected during the fieldwork, but given that they already have colonized the rest of the river, their presence in Miño is quite probable. The highest record of the rainbow trout in the mentioned study is 4,560 m in Misitune (1 °22'S), which means that elevation would not be an impediment to the potential expansion of the invasive fish into the habitat of T. halli.
Besides these anthropic influences, it is also necessary to consider natural factors that could constitute a threat to the population. The extreme north of Chile is affected by intense precipitations during the so-called Altiplanic winter, which generates flash floods and landslides, having a negative impact on the biota. This phenomenon reduces significantly the riparian vegetation (Paicho-Hidalgo et al. 2015) on which the frogs of the genus Telmatobius heavily depend, probably for shelter from UV radiation and predators. An example of this type of catastrophic event is what happened in the Vilama River (see above). A similar case is Amincha, type locality of T. philippii, where the effects of a recent swelling of the creek were observed in February 2018 (von Tschirnhaus, pers. obs.). The vegetation was severely damaged, and even though a few living specimens were detected, it took a long time to locate them. Paicho-Hidalgo et al. (2015) pointed out that the ecological resilience of these ecosystems allows quick revegetation, still, such an event in the habitat of T. halli could diminish the population and make it more vulnerable to other stresses. Comparing the current rock formations to those from the 1935 recordings suggests that destructive erosion events do occur in Miño.
All these threats, alone or in combination, could potentially lead to the extinction of T. halli if this species were restricted only to the source of the Loa River. Therein lies the importance of surveying the Loa River for the presence of Telmatobius, particularly its upper portion, where the watercourse and the surroundings are seemingly untouched for several kilometers, and of establishing the taxonomic status of the Miño population with respect to T. dankoi and T. vilamensis. In a broader context, the resolution of these aspects would contribute significantly to the taxonomy, biogeography and conservation of the