Fig. 2

Morphological variation among larval and adult ceratophryids. Figures are not in scale. a Chacophrys pierottii. a1 The C. pierottii larvae resemble a typical type IV tadpole [26]. a2 C. pierottii oral disk. The oral disk bears a single and continuous row of marginal papillae. The labial tooth row formula is 1 (1 + 1)/(1 + 1) 2. a3 Lateral view of C. pierottii larval head. An unusual and variable feature in C. pierottii larvae is a cutaneous nasal appendix of unknown function that projects forward between the nostrils in some individuals [27]. a4 Adult C. pierottii. Frogs of this species reach snout-vent lengths of about 55 mm. b Ceratophrys cranwelli. b1 The Ceratophrys tadpole has most of the features of type IV tadpoles, but the larva is modified for a macrophagous life style. Ceratophrys tadpoles first bite small prey and then ingest them whole, or chew larger prey into pieces before ingestion [28]. In Ce. ornata and Ce. cranwelli, the tadpoles emit underwater sounds that are thought to be a mechanism for avoiding cannibalism [29, 30]. b2 Ce. cranwelli oral disk. The oral disk has a single row of marginal papillae, which are few and spur-like. The labial tooth row formula is 3 (3 + 3)/(4 + 4) 3. The keratinized jaw sheaths are serrated. b3 Adult Ce. cranwelli. The mature frog is large (snout-vent length up to 130 mm), stout and aggressive. c Lepidobatrachus laevis. c1. The Lepidobatrachus tadpole has a flattened head and an extremely wide mouth, such that the maximum width of the head is at the level of its lower jaw articulation. The feeding mechanism consists of swallowing prey whole [31]. The tadpole’s branchial chambers open in bilateral cutaneous lateral flaps in which the forelimbs develop. Fast tail movements allow for rapid escape from predators (without the sound emissions seen in Ceratophrys). Cannibalism, as a strategy to survive when heterospecific prey are limited, has been witnesses in tadpoles of L. llanensis [28]. c2 L. laevis oral disk. The supralabial and lower jaw cartilages of the larva are transversally elongated. There is a single row of marginal papillae, which are small and few. The keratodonts are absent, and there is a vestigial, serrated keratinized upper jaw sheath. c3 Adult L. laevis. The mature frog, like the larvae, is dorsoventrally flattened with its eyes and nostrils positioned dorsally. Females L. laevis may reach snout-vent length of ~120 mm