Hypsiboas calcaratus (Figs 4C, 8C, and 9) is characterized by: (1) mean SVL 36.82 mm in males (range 27.61–42.50; n = 36), 50.92 mm in females (range 45.94–56.29; n = 4); (2) basal webbing on the fingers; (3) calcar large and triangular; (4) dorsal background color ranging from reddish brown to cream, pinkish white or grayish brown, in most cases dark marks are present (e.g., broad transversal marks, large black stains); (5) often middorsal dark brown line present; (6) flanks pale cream or gray (in life, blue in large females and light blue or white in males) with dark brown vertical bars; (7) hidden surfaces of thighs pale cream or gray (in life, blue in large females and light blue or white in males) with dark brown transversal bars; (8) ventral surfaces of thighs creamy white, yellowish white or brown; (9) venter creamy white or yellowish white; (10) webbing on feet; (11) in life, iris creamy silver or bronze with upper yellow to orange band; (12) prepollical spine present in males.

Hypsiboas calcaratus is most similar to Hypsiboas fasciatus and Hypsiboas almendarizae sp. n. It differs from both species by the shape of the calcar (large and triangular in Hypsiboas calcaratus, small and conical in Hypsiboas fasciatus, and large and conical in Hypsiboas almendarizae sp. n.; Fig. 14C–D) and by the number of notes in the advisement call (Fig. 12). Hypsiboas calcaratus can be further distinguished from Hypsiboas fasciatus by the color of the upper band in the iris: red to reddish brown in Hypsiboas fasciatus, yellow to orange in Hypsiboas calcaratus. Hypsiboas almendarizae sp. n. differs from Hypsiboas calcaratus in having narrower transversal dark bars on the flanks and thighs (mean width of bars on thighs = 5.05% of femur length, SD = 0.61, in Hypsiboas almendarizae sp. n. vs. 7.89%, SD = 1.2, in Hypsiboas calcaratus; differences are significant: t = -6.72, df = 18, P < 0.001) and smaller calcars.

Hypsiboas calcaratus differs from Hypsiboas maculateralis sp. n. in advertisement call (lower dominant frequency, higher fundamental frequency; Figs 12E–F and 13A–B) and by the presence of transversal bars on the flanks and hidden surfaces of the thighs (dark blotches instead of bars in Hypsiboas maculateralis sp. n.) Hypsiboas calcaratus can be distinguished from Hypsiboas alfaroi sp. n. and Hypsiboas tetete sp. n. by the presence of a calcar (instead of a small tubercle on the heel) and by the absence of dark flecks on the gular region and chest (present in Hypsiboas alfaroi sp. n. and Hypsiboas tetete. sp. n.) Morphological characters useful to differentiate Hypsiboas calcaratus from other species are shown in Table 6.

Variation in dorsal and ventral coloration of preserved specimens is shown in Figure 9. Background dorsal coloration varies from cream (e.g., QCAZ 40085) to pinkish white (e.g., QCAZ 44530), reddish brown (e.g., QCAZ 14957, 43256, 44422), pale reddish brown (e.g., QCAZ 43259) or pale grayish brown (e.g., QCAZ 48718). Irregular dorsal marks may be present in diverse patterns. A dark middorsal line extends from the tip of the snout to the mid-sacrum (e.g., QCAZ 43256), but in some specimens it only extends along the head (e.g., QCAZ 25514) or on the anterior half of the body (e.g., QCAZ 43131). There is variation in the number, size, and shape of dorsal marks. Some individuals (e.g., QCAZ 43256) have five to seven brown diffuse transversal bands (sometimes interconnected). Brown transversal bars are present on the dorsal surfaces of the limbs (one or two on the upper arm and forearm and three to five on the thigh, shank, and foot). In some individuals, the dorsum and dorsal surfaces of the forearms and shanks have large black stains (e.g., QCAZ 14957) or scattered brown or white dots (e.g., QCAZ 40085, 44178, 14971). The coloration of flanks and hidden surfaces of thighs vary from pale cream to creamy white or light gray, with dark brown transversal bars. The number of bars on the flank varies from 4 to 13; the number of bars on the thigh varies from 4 to 9. The extent of the area with bars varies from the groin to the mid flank (e.g., QCAZ 43259) to from the groin to the axilla (e.g., QCAZ 43256). In some individuals, the bars can also be present on the hidden surfaces of the shanks, ventral surfaces of the forelimbs, and dorsal surfaces of the feet (e.g., QCAZ 43256).

Ventral surfaces of preserved specimens vary from creamy white (e.g., QCAZ 44530) to yellowish white (e.g., QCAZ 43256). In some individuals, scattered minute pale brown blotches are present on the lips (e.g., QCAZ 31446, 44178). Coloration of webbing and discs vary from yellowish white to brown or gray. Coloration of bones is white or green.

(based on photographs; Figs 4C and 8C). Dorsal surfaces vary from light brown (e.g., QCAZ 40056) to reddish brown (e.g., QCAZ 36869) or brown (e.g., QCAZ 24282) with a middorsal dark brown line (e.g., QCAZ 40985); some individuals have brown diffuse transversal bands (e.g., QCAZ 43256); the dorsal surfaces of the limbs have pale brown transversal bars (e.g., QCAZ 43256); scattered minute white and black dots can be present on the dorsum (e.g., QCAZ 40056); in some individuals there are large dark brown blotches on the dorsum, dorsal surfaces of the forearms and shanks (e.g., QCAZ 43245); flanks are white, light blue or blue with dark brown vertical bars (e.g., QCAZ 40083); hidden surfaces of thighs and shanks are white, light blue or blue with dark brown transversal bars (e.g., QCAZ 43034); in some specimens there are dark brown transversal bars on the hidden surfaces of the shanks, ventral surfaces of the upper arms, and dorsal surfaces of the feet (e.g., QCAZ 43034); a faint creamy white stripe usually is evident on the outer edge of the feet, tarsus, forearms, and hands (e.g., QCAZ 26062); venter creamy white with belly yellowish white; ventral surfaces of hindlimbs and forelimbs translucent white (e.g., QCAZ 43824) or yellowish (e.g., QCAZ 40085); in some individuals, ventral surfaces of the thighs are creamy white (e.g., QCAZ 43047); discs and webbing yellowish (e.g., QCAZ 40085) or brown (e.g., QCAZ 40985); iris creamy silver (e.g., QCAZ 40056) or bronze (e.g., QCAZ 40085) with an upper yellow to orange band (e.g., QCAZ 43047); bones are white (e.g., QCAZ 40083) or green (e.g., QCAZ 43824).

In the examined adult series, the largest male has a SVL of 42.50 mm, and the largest female 56.29 mm; mean male SVL = 37.08 mm (n = 35; SD = 2.09), mean female SVL = 50.92 mm (n = 4; SD = 4.80). Females are significantly larger than males (t = -5.71, df = 3, P = 0.009). Inter-population variation in size and other morphometric variables is shown in Tables 1 and 2.

Two males were recorded at Tena (Provincia Napo) on 1 March 2009 and five males at Estación Científica Yasuní PUCE (Provincia Orellana) on 20 June 2009, in vegetation next to streams or ponds. Acoustic parameters of the advertisement call are shown in Table 7. The call (Fig. 12E–F) consists of a single quack note with a mean duration of 0.05 s (SD = 0.00) and mean rise time of 0.04 s (SD = 0.01). The mean dominant frequency is 1780.50 Hz (SD = 112.73) and the mean fundamental frequency is 557.13 Hz (SD = 46.21).

Hypsiboas calcaratus has confirmed records (based on DNA sequences and specimens listed in Appendix) from French Guiana, Guyana and the Amazon basin of Brazil, Ecuador, and Peru (Fig. 17). A photograph published by De la Riva et al. (2000) confirms its presence in Bolivia. Records from Colombia and Venezuela need confirmation. Known localities range in elevation from sea level (Kaw) to 650 m (Canelos).

Hypsiboas calcaratus occurs in Terra Firme forest, flooded forests (Várzea and Igapó), and swamps. It is generally found next to streams, ponds, and lakes. Individuals have been recorded at night perching on vegetation 15 to 200 cm above the ground. Their occurrence in secondary forests and artificial open areas suggest at least some tolerance of anthropogenic habitat disturbance.

Vegetation types at known localities include Southwest Amazon Moist Forest and Napo Moist Forest for the Peruvian and Ecuadorian localities, Guianan Moist Forest for the Guyana and French Guiana localities, and Madeira-Tapajós Moist Forest for the Brazilian locality (according to the World Wildlife Fund, 2012).

Its distribution polygon has 3’586,597 km² and overlaps with protected areas and large regions of pristine forest. Hypsiboas calcaratus is relatively frequent in scientific collections suggesting that, at least in part of its range, it is not a rare species. For these reasons we propose assigning Hypsiboas calcaratus to the Red List category of Least Concern.