English: Cotopaxi Rain Frog. Spanish: Cutín silbador.

This and the following sections are based on specimens of P. phoxocephalus listed in Suppl. material 2. A species of the Pristimantis phoxocephalus group having the following combination of characters: (1) dorsum shagreen with scattered small tubercles; faint middorsal fold; head with a middorsal row of two or more small tubercles; dorsolateral folds absent; anterior half of flanks with or without inconspicuous longitudinal lateral folds; skin on venter areolate to coarsely areolate; discoidal fold present or absent; (2) tympanic membrane and tympanic annulus prominent, its upper and posterolateral margin covered by supratympanic fold; (3) snout moderately long, acuminate with a fleshy keel in dorsal view, protruding in profile; (4) upper eyelid with small distinct rounded tubercles; cranial crests absent; (5) dentigerous processes of vomers low to prominent, oblique, moderately separated, posteromedial to choanae; (6) vocals slits, vocal sac and large nuptial pads present in adult males; (7) Finger I shorter than Finger II; discs of digits broadly expanded, rounded to elliptical; (8) fingers with lateral fringes; (9) small distinct ulnar tubercles (Fig. 23A); (10) heel bearing a small, subconical tubercle surrounded by smaller tubercles; outer edge of tarsus bearing a row of low subconical tubercles; inner edge of tarsus bearing a small inconspicuous fold followed by small subconical tubercles; (11) inner metatarsal ovoid, elevated, 4–6 times the size of round outer metatarsal tubercle; supernumerary tubercles low, numerous; (12) toes with broad lateral fringes; basal webbing between toes present; Toe V longer or much longer than Toe III (disc on Toe III reaches the middle to distal edge of penultimate subarticular tubercle on Toe IV, disc on Toe V reaches the middle to distal edge of distal subarticular tubercle on Toe IV); toe discs smaller than those on fingers, rounded to elliptical (Fig. 8D); (13) in life, dorsal coloration is cream, yellow, or brown with or without reddish or olive tones; dorsum with or without a longitudinal middorsal band, scapular W-shaped marking, chevrons, white or black flecking or pale botches; head with or without black or brown interorbital band, canthal stripe, supratympanic stripes, and labial bars; flanks with the same color or lighter than dorsum; groins, anterior and posterior surfaces of thighs, and concealed surfaces of tarsus and shanks yellow with black reticulations; ventral surfaces of thighs yellow; venter white with brown midline and reticulations; iris copper with or without a faint medial horizontal brown to reddish brown streak, with thin black reticulations (Fig. 26); (14) average SVL in adult females: 36.9 ± 2.2 mm (34.2–39.9 mm; n = 5); in adult males: 23.7 ± 2.9 mm (20.9–27.9 mm; n = 4).

Pristimantis phoxocephalus is most similar to P. atillo, P. jimenezi, P. teslai sp. nov., P. totoroi sp. nov., and P. verrucolatus sp. nov. However, the coloration of the groins and concealed surfaces of thighs (yellow coloration with dark brown to black reticulations) distinguishes it from the species above (orange in P. atillo; different shades of brown with light brown to yellow flecks, spots or blotches in the other species). It can be further distinguished from P. jimenezi by having an advertisement call with shorter inter-note interval and a lower frequency of the second harmonic and final frequency of the note (Table 6). Pristimantis teslai sp. nov. has a tuberculate dorsum while in P. phoxocephalus is shagreen. Pristimantis torresi sp. nov. differs from P. phoxocephalus in having a golden to beige iris with a red to reddish-brown medial streak (copper with or without a faint red streak in P. phoxocephalus), and a wider head relative to its body (males Z = -2.56285, p = 0.0104, HW/SVL = 33.4–34.4% in P. phoxocephalus, 34.2–37.8% in P. torresi sp. nov.; females Z = -2.08893, p = 0.0367, HW/SVL = 33.1–37.3% in P. phoxocephalus, 36.7–38.5% in P. torresi sp. nov.). Pristimantis totoroi sp. nov. is the most similar and geographically closest species; both species differ by the coloration of the groins and iris (copper with or without a brown streak in P. phoxocephalus; golden with a red streak in P. totoroi sp. nov.) and by the presence of more distinctive tubercles and dermal folds in P. totoroi sp. nov. The advertisement call of P. totoroi sp. nov. has shorter inter-note intervals than P. phoxocephalus (Table 6). Pristimantis verrucolatus sp. nov. differs from P. phoxocephalus by having large tubercles and warts on flanks and by its advertisement call. Calls of P. verrucolatus sp. nov. have one note (3–9 in P. phoxocephalus) that lasts more than the notes of the calls of P. phoxocephalus, and the dominant frequency, second harmonic frequency, and final and initial frequency of the notes are lower (Table 6; Fig. 6).

Variation in live and preserved individuals is shown in Figures 26, 27. This section is based on 23 individuals of the QCAZ collection collected at the type locality and its surroundings. Photographs are available from 12 individuals. Coloration in life is mentioned in parenthesis. Skin on dorsum is shagreen with scattered prominent tubercles; dorsum bears a faint middorsal fold; a middorsal row of two or more tubercles is present on the head; lateral folds are inconspicuous or absent. Folds and tubercles in juveniles are more prominent and larger than those in adults. In preservative, middorsal fold, lateral folds, and tubercles on dorsum can be lost. Dorsal coloration varies from cream, light gray and light brown to dark brown (cream, pale yellow or light to dark brown with or without reddish or olive tones). Dorsum can have a scapular W-shaped marking, chevrons, longitudinal middorsal band, pale blotches, and black or white flecking. Dorsal markings in juveniles are more evident than those in adults. Groins, anterior and posterior surfaces of thighs, and concealed surfaces of tarsus and shanks are uniformly white (yellow) in juveniles. Adults bear dark brown to black reticulations outlining well-defined pale (yellow) spots. Dorsal surfaces of thighs bear dark oblique bars, well defined on juveniles, ill-defined or absent on adults. Ventral surfaces of thighs are white or cream (yellow). Venter is white with a light brown midline (reddish cream) extending to the throat; throat is white (cream, sometimes yellow in males). Iris is copper with black reticulations in adults; sclera varies from cream to light blue. Juveniles have a faint medial horizontal red streak.

Based on recordings of two non-collected individuals at the type locality of P. phoxocephalus (November 17, 2014; 19h26; <10 °C). Advertisement calls of P. phoxocephalus consist of a series of 3–9 sharp notes (Fig. 6B). Notes last on average 0.154 s (range 0.133–0.175 s), silences between them, 0.135 s (range 0.110–0.159 s). The exact middle of the note presents the highest energy. The dominant and fundamental frequency of the notes is 2578 Hz. The note increases its frequency from beginning to end (2587–2452 Hz on average). Descriptive statistics for bioacoustic parameters are shown in Table 6.

Pristimantis phoxocephalus is known from its type locality, Pilaló, Cotopaxi Province, Ecuador, at 2340–2820 m a.s.l. (Fig. 2), which corresponds to Western Montane Forest. Individuals collected for this study were found by day inside bromeliads at 2–4 m above the ground. These bromeliads were on scattered trees within pastures. Lynch (1979) provides more ecological data for specimens collected at the type locality.

Currently, P. phoxocephalus is considered to be a Least Concern species (Rodríguez et al. 2004) under the assumptions: (i) Extent of Occurrence < 20000 km², (ii) common and adaptable species with a presumed large population, (iii) unlikely to be declining fast enough to qualify for a more threatened category. After assessing the identity of this species, herein we assign it to the Critically Endangered Red List category following the B1ab(iii)+2ab(iii) IUCN criteria because: (i) it is known from one locality whose habitat is constantly degrading due to human settlements and cattle raising, (ii) Extent of Occurrence < 100 km², (iii) Area of Occupancy < 10 km².

Until now, P. phoxocephalus has been considered a single highly polymorphic species (e.g., Lynch 1979; Lynch and Duellman 1997; Duellman and Lehr 2009). We show that most populations previously ascribed to P. phoxocephalus represent other species (e.g., Pristimantis atillo, P. jimenezi, P. teslai sp. nov., P. torresi sp. nov., P. totoroi sp. nov., P. verrucolatus sp. nov., Pristimantis sp. (CCS2), Pristimantis sp. (UCS2), Pristimantis sp. (UCS3)). To determine the true identity of P. phoxocephalus, we made collections at the type locality (Pilaló, Cotopaxi Province, see Suppl. material 2 for the list of specimens). Surprisingly, sequences from Pilaló fell in two distinct clades, indicating the presence of two species. One juvenile (QCAZ 58425), collected at 2258 m, is actually P. totoroi sp. nov. All other specimens (e.g., QCAZ 58463) are P. phoxocephalussensu stricto. Examination of photographs of the holotype KU 142075 (Fig. 23A) showed unequivocally that it is conspecific with the specimens from the highland population. We included in our analysis sequences of “P. phoxocephalus” from two localities of Peru (Kañaris in Ferrenafe Province, Warmicocha-Cochapamba road in Chachapoyas Province); they do not belong to Huicundomantis (Suppl. material 3) and likely represent an undescribed species. Hence, P. phoxocephalus is endemic to Ecuador and has a restricted distribution.