Comprehensive DescriptionRead full entry
Triprion petasatus is a frog with a snout-vent length of 48.1 mm to 60.8 mm in males and 65.0 mm to 75.2 mm in females. Its head is large and in the form of a bony casque, with skin completely attached (co-ossified) to the skull. It has an large, expanded, upturned prenasal bone (distinguishing it from all other Middle American casque-headed hylids) and expanded maxillaries, which together form a broad, labial shelf with a serrate edge. The snout protrudes far beyond the leading edge of the lower jaw. Nostrils are dorsal, located at about two thirds of the distance from the eye to the tip of the snout. At the anterior edge of the eye, there is a bony, preorbital knob, which is sometimes so enlarged that it hangs over the eye's anterior edge. A sharp canthal ridge extends from this preorbital knob to a point just posterior to the nostril. The eyes are large, protuberant, and directed anterolaterally. There is a bony, supratympanic ridge extending from the posterior edge of the eye to the posterior edge of the skull. This ridge hangs over the upper edge of the tympanum, which would otherwise be distinct. There is also a finely serrate bony ridge, generally with a medial notch, delimiting the posterior edge of the skull (Duellman 2001).
The upper arms are slender, while the forearms are robust. The wrist has a transverse dermal fold. The fingers are moderately long and robust, with greatly expanded discs; the diameter of the third finger disc approximately equals the diameter of the tympanum. Both suberarticular tubercles and supernumerary tubercles are large and round. This frog also has a large, flat, palmar tubercle. Males possess nuptial pads, which extend along the inner edge of the thumb to the disc. Webbing is lacking between fingers 1 and 2 and is rudimentary thereafter. The hind legs are short when adpressed, with the heels barely overlapping. There is a well-defined tarsal fold extending along the full length of the tarsus. The inner metatarsal tubercle is large, flat, and elliptical, while the outer metatarsal tubercle is minute and round. The toes are long, about 2/3 webbed, and have discs slightly smaller than those on the fingers. On the feet, the subarticular tubercles are round and somewhat larger than the supernumerary tubercles. The frog has smooth skin on its dorsum (except its head), chin, and ventral surfaces of its limbs (except its thighs). The skin is granular on the flanks and belly (Duellman 2001).
Males are generally an olive green while females are tan or sometimes olive-brown, with dark brown or black markings on the back, shanks, and forearms, but not the head. In some individuals there are silvery gray flecks on the dorsum, especially the head. Flanks are olive-green or yellow-green. Dark brown or black transverse bands are usually present on thighs and feet but may be lacking in some specimens. The posterior surfaces of the thighs are dark brown or reddish brown, and the anterior surfaces are pale brown. The frog has a white belly and tan ventral surfaces on the shanks and feet. It has a golden bronze iris with black reticulations. Breeding males have yellow vocal sacs with brown flecks, as well as nuptial pads (Duellman 2001).
Tadpoles have been measured at 12.3 mm body length and 27.0 mm total length at stage 30. The tadpole has an ovoid body, which is slightly wider than it is deep. Its tail is moderately deep, and pointed terminally. Its snout is bluntly rounded in dorsal profile, but acutely rounded in lateral profile. The nostrils are directed dorsolaterally. Its eyes are relatively small and dorsolateral. Its mouth is moderately small and anteroventral. Lips are each bordered by a row of small papillae, interrupted medially above the upper lip, with more papillae present in lateral folds on either side of the lips. The beaks are moderately heavy with small, pointed serrations. The upper beak is shaped like a high arch with long, slender, lateral processes, while the lower beak is broadly V-shaped. Two upper and three lower rows of teeth are present, with the upper rows equal in row length, but lower rows getting progressively less wide. The spiracle is long and sinistral, opening just below the midline at a point about midlength on the body. The vent is short and dextral. The tadpole has moderately heavy caudal musculature which does not extend to the tip of the tail. At the midlength of the tail, the depth of the musculature is equal to the depth of either fin (Duellman 2001).
The tadpole is a dull, grayish-brown color with a creamy, tan caudal musculature. Its fins are transparent with brown reticulations. The iris is pale bronze (Duellman 2001).
This frog's cranial osteology has been studied in some detail (Trueb 1970). The specific namepetasatus is derived from Latin, meaning "with a hat on". This designation refers to its helmet-like casque (Duellman 2001).