Ceratophrys cranwelli is a large, robust frog. Adult snout–vent length varies widely from 42 to 130 mm (Valetti et al. 2012; Schalk and Fitzgerald 2015). Snout-vent length of metamorphs is between 25 and 43 mm (Schalk and Fitzgerald 2015). This species has a large, flat, wide head with prominent eyes and lenticular pupils. It has characteristic triangular “horned” ridges above the eyes (Barrio 1980; Valetti et al. 2012). The jaw articulation occurs at the the craniovertebral joint level (Fabrezi 2011), which gives this species an unusually large gape that is more than half as wide as the snout-vent length (Schalk and Fitzgerald 2015). This species also has non–pedicellate teeth with a broad base curved into sharp points—an unusual dentition among frogs (Lappin et al. 2017). Fingers are short and non–webbed; toes are slightly webbed (Barrio 1980).
Tadpoles at Gosner developmental stages 39 – 42 generally have an snout-vent length of about 25 – 31 mm and a total length of roughly 57 – 68 mm (Fabrezi 2011). Mouthparts have very keratinized jaw sheaths, which are well-adapted for tearing prey items (Vera Candioti 2005).
Ceratophys cranwelli was once considered the same species as C. ornata, but they can now be distinguished by several features. Ceratophrys cranwelli is diploid (2n = 26), whereas C. ornata is octoploid (8n = 104). Ceratophrys cranwelli can also be distinguished from C. ornata by the triangular ridges above the eyes of C. cranwelli, which are not prominent in C. ornata (Barrio 1980; Valetti et al. 2012). The two species also have different cranial proportions. Ceratophrys cranwelli is known to have more muted colors, whereas C. ornata is more brightly colored and may contain some reds; C. cranwelli may also have a trident pattern on the dorsal aspect, which is absent in C. ornata (Barrio 1980). The two species occupy separate geographic regions: C. ornata occupies parts of Argentina, Uruguay and Brazil, while C. cranwelli is found in more northern regions (Brusquetti and Lavilla 2006). However, along the border of these species’ ranges, individuals of either species may not be as readily distinguished—in these cases, only a karyotype will definitively identify the species (Barrio 1980).
In life, C. cranwelli is light brown to muted green with dark brown dorsal spots and a pale underbelly (Barrio 1980; Valetti et al. 2012). The pattern of the spots gives the frog a trident–like pattern on its dorsal aspect (Barrio 1980). There are dark brown bands covering the forelimbs transversely (Valetti et al. 2012).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Argentina, Bolivia, Brazil, Paraguay
This species is found in the Gran Chaco, which is an ecoregion spanning Argentina, Bolivia, Brazil and Paraguay. The frogs live within and around ephemeral ponds but were not observed in a semipermanent pond or far from ponds (Reichle et al. 2004, Schalk and Fitzgerald 2015). They may be found at altitudes as high as 700 m asl (Reichle et al. 2004).
Life History, Abundance, Activity, and Special Behaviors
This species is normally fossorial, although they become more active and terrestrial during the rainy season (Faivovich et al. 2014). They are found in and around ephemeral ponds (Schalk and Fitzgerald 2015).
They breed during the early rainy season (Valetti et al. 2012). Females are oviparous and lay eggs in ponds, which hatch into tadpoles (Fabrezi 2011); the clutch size in one study was 1200 eggs (Salgado Costa et al. 2014).
The tadpoles are carnivorous and are known to eat other tadpoles (including those within their own species), insects, and crustaceans, among other animals (Vera Candioti 2004). The adults are sit–and–wait predators; their diet consists of an array of vertebrates, including other anurans, accommodated by C. cranwelli’s large gape (Schalk et al. 2014) and strong bite force (Lappin et al. 2017).
Ceratophrys cranwelli possesses the ability to produce sounds even as tadpoles. In one study, tadpoles between Gosner stages 25 and 42 emitted underwater sounds when interacting with conspecifics. In an environment with a low predator:prey ratio, in which there was relatively more heterospecific prey, there were fewer instances of cannibalism than when there was a high predator:prey ratio. This supports the idea that underwater sound emissions play some role in predator avoidance within the species, but they are less successful when heterospecific prey is scarce (Salgado Costa et al. 2014).
Adult males of this species call. The call consists of a series of vocalizations that begin at a low intensity before peaking in the middle and falling back down; it has been described as sounding like a bass horn. The call has a dominant frequency range of 1,400 – 1900 Hz, a pulse rate of around 0.192 pulses/ms, and a call duration of roughly 319 – 358 ms (Salas et al. 1998; Valetti et al. 2012). Pulse rate and call duration are dependent on temperature, with pulse rates increasing and call duration decreasing with increasing temperature. Males typically call throughout the night while partially submerged in ponds (Valetti et al. 2012).
Trends and Threats
When this species was last assessed by IUCN in 2004, the population trend was found to be decreasing, however the species was listed as “Least Concern” because of its wide distribution. Factors that may be contributing to this include persecution by people within their range who believe the frogs to be venomous; collection for sale in the pet trade; and collection of eggs for research (Reichle et al. 2004). Eight percent of C. cranwelli’s range lies within protected areas (Nori et al. 2016).
Relation to Humans
Ceratophrys cranwelli is commonly sold in the pet trade as Pac–Man frogs. Within their range, they are collected for the pet trade and sometimes intentionally killed due to the misbelief that they are venomous; eggs are collected for sale within the scientific research community (Reichle et al. 2004).
Possible reasons for amphibian decline
General habitat alteration and loss
Intentional mortality (over-harvesting, pet trade or collecting)
Recent molecular phylogenetic analysis suggests that C. cranwelli is the sister taxon of C. ornata. The genes included in this study were cytochrome oxidase I, cytochrome b, NADH dehydrogenase subunit 1, tRNAVal, tRNALeu, tRNAIle and an additional section of 16S, as well as homolog 1, rhodopsin, tyrosinase, recombination–activating gene 1, proopiomelanocortin A gene and chemokine receptor 4 and analyzed by parsimony analysis (Faivovich et al. 2014).
The genus name, “Ceratophrys”, is derived from the Greek word for “horn”, κέρατο, in reference to the horn–like protrusions above the eye in adults (Barrio 1980).
The specific name, “cranwelli”, is in honor of Dr. Jorge Cranwell, who was the first person to observe and identify C. cranwelli as a species separate from C. ornata (Barrio 1980). Cranwell managed the herpetology collection of the Museo Argentino de Ciencias Naturales in Buenos Aires, Argentina, and wrote the field guide Para la herpetología de Misiones (Beolens et al. 2013).
Barrio, A. (1980). "Una nueva especie de Ceratophrys (Anura, Ceratophryidae) del dominio Chaqueno." Physis (Buenos Aires), 39(96), 21-30.
Beolens, B., M. Watkins, M. Grayson (2013). The Eponym Dictionary of Amphibians. N.p: Pelagic.
Brusquetti, F., and Lavilla, E.O. (2006). ''Lista comentada de los anfibios de Paraguay.'' Cuadernos de Herpetologica, 20, 3-79.
Fabrezi, M. (2011). "Heterochrony in growth and development in anurans from the Chaco of South America." Evolutionary Biology, 38(4), 390–411. [link]
Faivovich, J., Nicoli, L., Blotto, B.L., Pereyra, M.O., Baldo, D., Barrionuevo, J.S., Fabrezi, M., Wild, E.R., Haddad, C.F.B. (2014). "Big, bad, and beautiful: phylogenetic relationships of the horned frogs (Anura: Ceratophryidae)." South American Journal of Herpetology, 9(3), 207-277. [link]
Lappin, A. K., Wilcox, S. C., Moriarty, D. J., Stoeppler, S. A., Evans, S. E., Jones, M. E. (2017). "Bite force in the horned frog (Ceratophrys cranwelli) with implications for extinct giant frogs." Scientific reports, 7(1), 1-10. [link]
Nori, J., Torres, R., Lescano, J.N., Cordier, J.M., Periago, M.E. and Baldo, D. (2016). "Protected areas and spatial conservation priorities for endemic vertebrates of the Gran Chaco, one of the most threatened ecoregions of the world." Diversity and Distributions, 22, 1212-1219. [link]
Reichle, S., Aquino, L., Silvano, D., di Tada, I. (2004). “Ceratophrys cranwelli.” The IUCN Red List of Threatened Species 2004: e.T56338A11464257. http://dx.doi.org/10.2305/IUCN.UK.2004.RLTS.T56338A11464257.en
Salas, N. E., Zavattieri, M. V., Tada, I. E. D., Martino, A. L., Bridarolli, M. E. (1998). "Bioacustical and etho-ecological features in amphibian communities of southern Córdoba province (Argentina)." Cuadernos de Herpetología, 12, 37-48. [link]
Salgado Costa, C., Chuliver Pereyra, M., Alcalde, L., Herrera, R., Trudeau, V. L., Natale, G. S (2014). "Underwater sound emission as part of an antipredator mechanism in Ceratophrys cranwelli tadpoles." Acta Zoologica, 95(3), 367-374. [link]
Schalk, C. M., Fitzgerald, L. A. (2015). "Ontogenetic shifts in ambush–site selection of a sit-and-wait predator, the Chacoan Horned Frog (Ceratophrys cranwelli)." Canadian Journal of Zoology, 93(6), 461-467. [link]
Schalk, C. M., Montaña, C. G., Klemish, J. L., Wild, E. R. (2014). "On the diet of the frogs of the Ceratophryidae: Synopsis and new contributions." South American Journal of Herpetology, 9(2), 90-105. [link]
Valetti, J. A., Salas, N. E., Martino, A. L. (2012). "Bioacústica del canto de advertencia de Ceratophrys cranwelli (Anura: Ceratophrydae)." Revista de Biología Tropical, 61(1), 273-280. [link]
Vera Candioti, M. F. (2005). "Morphology and feeding in tadpoles of Ceratophrys cranwelli (Anura: Leptodactylidae)." Acta Zoologica, 86(1), 1-11. [link]
Originally submitted by: Tiffany Gonzalez (2021-03-26)
Edited by: Ann T. Chang (2021-09-30)
Species Account Citation: AmphibiaWeb 2021 Ceratophrys cranwelli: Cranwell’s Horned Frog <https://amphibiaweb.org/species/5721> University of California, Berkeley, CA, USA. Accessed Oct 18, 2021.
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Citation: AmphibiaWeb. 2021. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 18 Oct 2021.
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