English: Atillo Rain Frog. Spanish: Cutín de Atillo.

QCAZ 42500, an adult male from Sangay National Park, Ranger Station, Atillo, Morona Santiago Province, Ecuador (2.1867S, 78.4963W, 3400 m), collected by Elicio Tapia on May 19, 2009. Figures 10A, 11A.

(44: 28 males, 5 females, 11 juveniles). All from Sangay National Park, nearby the type locality. Ecuador: Chimborazo Province: QCAZ 2298–302, QCAZ 2304, adult males, QCAZ 2303, QCAZ 2305–306, juveniles (2.1749S, 78.5047W, 3600 m), collected by Giovanni Onore and Luis Coloma in October 1991; QCAZ 3110, adult female, QCAZ 3111–112, adult males (2.1749S, 78.5047W, 3600 m), collected by Luis Coloma in January 1991; QCAZ 40593, QCAZ 40594, adult females (2.2103S, 78.4991W, 3730 m), collected by Diego Almeida, Galo Díaz, Ítalo Tapia, and Martín Bustamante in May 2003. Morona Santiago Province: QCAZ 31946, adult male (2.1989S, 78.4824W, 3185m), collected by Charles M. Kieswetter and Ítalo Tapia in April 2006; QCAZ 40584, adult male (2.2024S, 78.4697W, 3366 m), collected by Diego Almeida, Galo Díaz, Ítalo Tapia and Martín Bustamante in May 2002; QCAZ 42501, adult female, QCAZ 40897, QCAZ 42483–486, QCAZ 42488–492, QCAZ 42499–500, QCAZ 42502–505, adult males, QCAZ 42493, QCAZ 42496, QCAZ 42498, QCAZ 42506, QCAZ 42512, QCAZ 42543, QCAZ 42548, juveniles (2.1867S, 78.4963W, 3400 m), collected by Elicio Tapia on May 18–19, 2009; QCAZ 59274, adult female, QCAZ 59214, QCAZ 59261, adult males (2.1842S, 78.4972W, 3436 m), collected by Francy Mora, David Velalcázar, Javier Pinto, Luis Tipantiza, Keyko Cruz, Daniel Rivadeneira, Freddy Almeida, Pol Pintanel, and Nadia Páez in March 2015. QCAZ 59228, adult male, QCAZ 59276, juvenile (2.1887S, 78.4823W, 3299 m), collected by Francy Mora, David Velalcázar, Javier Pinto, Luis Tipantiza, Keyko Cruz, Daniel Rivadeneira, Freddy Almeida, Pol Pintanel, and Nadia Páez in March 2015.

A member of the Pristimantis phoxocephalus group having the following combination of characters: (1) skin on dorsum shagreen with or without scattered small subconical tubercles; middorsal fold ill-defined or absent; head with a middorsal longitudinal row of two or more subconical tubercles; dorsolateral folds absent; skin on venter areolate; discoidal fold present or absent; (2) tympanic membrane and tympanic annulus prominent, its upper and posterior margin concealed by supratympanic fold; (3) snout moderately long, acuminate with a fleshy keel in dorsal view, protruding in profile; (4) upper eyelid with one or more small prominent subconical tubercles surrounded by lower tubercles; cranial crests absent; (5) dentigerous processes of vomers low to prominent, oblique, moderately separated, posteromedial to choanae; (6) males having vocal slits, external vocal sac and white nuptial pads; (7) Finger I shorter than Finger II; discs of digits expanded to broadly expanded, rounded to elliptical; (8) fingers with broad lateral fringes; (9) ulnar tubercles low and rounded, sometimes connected by an ill-defined fold; (10) heel bearing one subconical tubercle surrounded or not by smaller rounded tubercles; outer edge of tarsus bearing low subconical tubercles; inner edge with or without ill-defined tubercles, short inner tarsal fold present; (11) inner metatarsal tubercle ovoid, elevated, five times the size of round outer metatarsal tubercle; supernumerary plantar tubercles numerous; (12) toes with lateral fringes, less conspicuous than those on fingers; basal webbing on feet (Fig. 7A); Toe V longer or much longer than Toe III (disc on Toe III reaches or exceeds distal edge of the penultimate subarticular tubercle on Toe IV, disc on Toe V reaches or exceeds distal edge of the distal subarticular tubercle on Toe IV); toe discs nearly as large as those on fingers; (13) in life, dorsal coloration varies from pale to dark brown; black or brown interorbital stripe, supratympanic stripe, and labial bars present; flanks with black dots and flecks arranged in a diagonal pattern, bordering light reticulations; groins, axils, concealed surfaces of thighs, and shanks orange; venter and throat cream to white; iris copper with a faint medial horizontal darker streak and black reticulations (Fig. 11); (14) average SVL in adult females: 31.3 ± 2.3 mm (29.4–35.3 mm; n = 5); in adult males: 24.7 ± 2.5 mm (17.5–28.1 mm; n = 29).

Pristimantis atillo is similar to other species with acuminate and protruding snouts of this group such as P. jimenezi sp. nov., P. phoxocephalus, P. teslai sp. nov., P. torresi sp. nov., P. totoroi sp. nov., and P. verrucolatus sp. nov. The bright orange coloration of its groins and posterior surfaces of thighs distinguishes it from them (brown with small light brown to yellow spots in P. jimenezi sp. nov.; yellow with black reticulations in P. phoxocephalus; dark brown with yellow irregular blotches in P. teslai sp. nov.; brown with or without yellow spots in P. torresi sp. nov.; reddish brown with small light brown to yellow spots in P. verrucolatus sp. nov.). Pristimantis atillo can be further distinguished from P. jimenezi sp. nov. and P. phoxocephalus by the presence of its characteristic black dots in the flanks (black dots absent in P. jimenezi sp. nov. and P. phoxocephalus). Pristimantis atillo differs from P. teslai sp. nov. by the dorsal skin texture (shagreen in P. atillo; tuberculate in P. teslai sp. nov.). The copper coloration of the iris differentiates P. atillo from P. torresi sp. nov. and P. totoroi sp. nov., whose iris is golden with a red streak. Furthermore, tubercles and folds of P. totoroi sp. nov. are more prominent than those of P. atillo, and its head, relative to the body, is longer (males Wilcoxon’s Z = 4.50124, p < 0.001, HL/SVL = 33.5–38.5% in P. atillo, 34.2–38.7% in P. totoroi sp. nov.; females Z = 2.43599, p = 0.0149, HL/SVL = 33.1–36.6% in P. atillo, 35.2–37.6% in P. totoroi sp. nov.). Pristimantis verrucolatus sp. nov. differs from P. atillo in having large tubercles and warts on its flanks. Pristimantis atillo is similar to P. modipeplus (Lynch 1981) in coloration pattern; P. modipeplus has a subacuminate snout in dorsal view and rounded in profile, lacks basal webbing between toes, and large females bear low cranial crests (Lynch 1981); meanwhile, P. atillo has an acuminate and protruding snout with a keel at the tip, presents basal webbing between toes and has no cranial crests.

Adult male (QCAZ 42500, SC28232). Measurements (in mm): SVL 26.3; TL 12.0; FL 11.9; HL 8.9; HW 9.1; ED 2.6; TD 1.3; IOD 2.8; EW 2.4; IND 2.1; EN 2.7; TED 1.1. Head narrower than body, slightly wider than long; snout moderately long, acuminate with triangular fleshy keel in dorsal view, protruding in profile; nostrils slightly protuberant, directed laterally with slight dorsal inclination; canthus rostralis concave in dorsal view, rounded in cross section; loreal region slightly concave; cranial crests absent; upper eyelid bearing one small but distinct conical tubercle surrounded by few indistinct smaller tubercles; tympanic membrane and annulus prominent, its upper and posterior margins concealed by supratympanic fold; two enlarged conical postrictal tubercle surrounded by indistinct low tubercles. Choanae median, elliptical, non-concealed by palatal shelf of maxilla; dentigerous processes of vomers prominent, oblique, moderately separated, posteromedial to choanae; each vomer bearing several indistinct teeth; tongue slightly longer than wide, posteriorly notched, posterior two-thirds free; vocal slits slightly curved, located at posterior half of mouth floor in between tongue and margin of jaw; vocal sac present.

Skin on dorsum shagreen; head with a row of two middorsal tubercles; dorsolateral folds absent; flanks with slightly larger tubercles than those on dorsum; skin on throat, chest, belly and ventral surfaces of thighs areolate; discoidal fold absent. Two distinct, low and round ulnar tubercles connected by an ill-defined fold; white nuptial pads present; palmar tubercles prominent, outer palmar tubercle bifid, slightly bigger than ovoid thenar tubercle; subarticular tubercles prominent, rounded; distinct, low supernumerary tubercles at base of fingers; fingers with broad lateral fringes; Finger I shorter than Finger II; discs on fingers expanded and elliptical; ventral pads on fingers surrounded by circumferential grooves (Fig. 7A).

Hindlimbs slender; dorsal surfaces of hindlimbs with scattered low round tubercles; posterior surfaces of thighs smooth, ventral surfaces of thighs areolate; heel bearing one low conical tubercle surrounded by some lower rounded tubercles; outer edge of tarsus bearing low subconical tubercles; inner edge of tarsus with ill-defined tubercles; short inner tarsal fold present; inner metatarsal tubercle ovoid, elevated, five times the size of circular, rounded, outer metatarsal tubercle; plantar surface with numerous indistinct supernumerary tubercles; subarticular tubercles prominent, rounded; toes with broad lateral fringes; small basal webbing between toes; discs nearly as large as those on fingers; discs on toes expanded, elliptical; all toes having ventral pads and circumferential grooves; relative lengths of toes: I<II<III<V<IV; Toe V much longer than Toe III (disc on Toe III reach distal edge of penultimate subarticular tubercle on Toe IV, disc on Toe V reaches distal edge of distal subarticular tubercle on Toe IV; Fig. 7A). Coloration of the holotype in preservative and life is shown in Figures 10, 11.

This section is based on 45 preserved specimens of the type series and photographs available for 11 individuals. Variation in living and preserved individuals is shown in Figures 11, 12. Coloration in life is mentioned in parenthesis. Dorsum varies from pale to dark brown with or without lighter irregular marks or white spots scattered on dorsum, few individuals have several thin parallel longitudinal stripes or a middorsal band (i.e., longitudinal pattern); the interorbital band can be thin to broad, paler or darker than background and is absent in individuals with longitudinal pattern; interscapular blotch is often present. Flanks have pale oblique reticulations usually surrounded by dark stripes formed by rows of black flecks. Groins, anterior and posterior surfaces of thighs cream (orange, in most cases surrounded by yellow blotches; an individual has yellow groins (QCAZ 42502)). Dorsal surfaces of thighs with brown to black oblique stripes. Venter and throat coloration varies from cream to white (cream to white with different levels of transparency, with or without ill-defined yellow blotches) with or without black flecks. Iris is reddish to orangey copper with a faint medial horizontal darker streak and thin black reticulations; sclera varies from white to light blue.

Coloration of holotype in preservative. Dorsum brown with lighter markings including W-shaped scapular mark, interscapular blotch, and faint irregular reticulations; head with light brown interorbital band; face with faint canthal and labial bars; dark brown supratympanic bar; flanks light brown with pale oblique reticulations surrounded by rows of black flecks; armpits, groins, anterior and posterior surfaces of thighs cream; dorsal surfaces of hindlimbs brown with lighter transversal bands; limbs with scattered black flecks; ventral surfaces cream; plantar and palmar surfaces dirty cream (Fig. 10A).

Coloration of holotype in life. Based on studio photographs (Fig. 11A). Dorsum brown with cream light markings including a W-shaped scapular mark, interscapular blotch, and irregular reticulations; head with light brown interorbital band; face with faint brown canthal and labial bars; dark brown supratympanic bar; flanks light brown with yellow reticulations surrounded by rows of black flecks; armpits, groins, anterior and posterior surfaces of thighs and shanks orange; dorsal surface of hindlimbs with faint yellowish brown transverse bands and scattered black flecks; venter yellowish white; vocal sac, chest, and ventral surfaces of forelimbs surfaces transparent pinkish cream; ventral surface of thighs yellow suffused with orange; plantar and palmar surfaces dirty cream; iris copper with a faint medial horizontal darker streak and thin black reticulations; light blue sclera.

This species is only known from the type locality, surroundings of Lagunas de Atillo, and nearby locations at Sangay National Park, between 3185 and 3730 m a.s.l (Fig. 1). This corresponds to the Eastern Montane Forest and Paramo biogeographic regions. Most individuals collected at night were found active on low vegetation, from ground level up to 1 m above the ground; an individual was collected from a bromeliad 2.5 m above the ground. During the day, they were found beneath rocks. Most collections were made on roadsides. Calling males have been found in March.

According to available data, this species has a very restricted distribution (Extent of Occurrence 7 km², Area of Occupancy 16 km²). However, less accessible adjacent areas in Sangay National Park are unexplored and represent potential distribution areas for this species. Therefore, we consider this species to be Data Deficient (IUCN 2017).

The specific epithet refers to the type locality of this species, the surroundings of Lagunas de Atillo, a lake complex in Sangay National Park, a UNESCO World Heritage Site.