Dorsal shields and octoploidy: extraordinary Pacman frogs
I was finally able to see some live South American horned frogs or Pacman frogs (Ceratophryidae), albeit captive specimens at Napoli Exotic. This is my favourite group of frogs and there's lots of cool stuff to say about them.
The group comprises three extant genera: Lepidobatrachus (three extant species), Ceratophrys (eight extant species), and Chacophrys, solely represented by the Chaco horned frog (C. pierottii) (e.g. Faivovich et al. 2014; Gómez and Turazzini 2021; Barcelos et al. 2022; O'Shea and Maddock 2024; van der Kamp and Ortega-Andrade 2024).
These South American frogs are usually large (females of the largest species, the Brazilian horned frog C. aurita, can measure 178 mm SVL), with large skulls (hyperossified in adult individuals), a wide gape, non-pedicellate fang-like teeth on the upper jaw, and tusk-like odontoids on the lower jaw (Lappin et al. 2017; Gómez and Turazzini 2021; Barcelos et al. 2022; O'Shea and Maddock 2024).
The strength of their bite is surprisingly high, with the largest specimens of Brazilian horned frog estimated to have a bite force of 248.6 N at the jaw tips and 497.1 N at the jaw midpoint (Lappin et al. 2017).
They are notoriously voracious sit-and-wait predators capable of subduing relatively large prey, up to their own size (Duellman and Lizana 1994; Schalk et al. 2014; Lappin et al. 2017; O'Shea and Maddock 2024).
Tadpoles of both Ceratophrys and Lepidobatrachus are also predatory, though those of the former employ keratinized jaw sheaths and keratodonts to dispatch prey, while those of the latter lack these features and instead engulf prey whole. The tadpoles of Chacophrys are instead herbivorous or detritivorous (Duellman and Lizana 1994; O'Shea and Maddock 2024).
While species of Ceratophrys and Chacophrys are predominantly terrestrial, with eyes positioned at the top of the head (under flashy "horns" in the former), species of Lepidobatrachus are predominantly aquatic, with more flattened bodies and dorsally positioned eyes (O'Shea and Maddock 2024).
Various (though not all) species of Lepidobatrachus and Ceratophrys possess a dorsal shield of bony plates: the morphology and formation of these structures is different in the two taxa, and may have been acquired independently (Barcelos et al. 2022).
They are fossorial, estivating underground during the dry season, during which many species are known to produce a cocoon of dead skin for water retention, only to come out during the rainy season (Faivovich et al. 2014; O'Shea and Maddock 2024; van der Kamp and Ortega-Andrade 2024).
Their fossil record is surprisingly good for anuran standards, dating back to the Miocene (Faivovich et al. 2014; Gómez and Turazzini 2021; Barcelos et al. 2022; Turazzini and Gómez 2023; van der Kamp and Ortega-Andrade 2024).
Features like estivation with cocoon formation and short larval period suggest that most diversification within the group occurred in semi-arid environments, with subsequent invasions of more humid regions (exemplified by species like the Surinam or Amazonian horned frog below) (Faivovich et al. 2014; van der Kamp and Ortega-Andrade 2024).
The interrelationships within the group, as well as its position within Hyloidea, are also disputed, with some studies finding Ceratophrys to be the sister group of a clade formed by Chacophrys and Lepidobatrachus, while others find Chacophrys to be the sister group of a Ceratophrys-Lepidobatrachus clade (e.g. Faivovich et al. 2014; Gómez and Turazzini 2021; Barcelos et al. 2022; van der Kamp and Ortega-Andrade 2024).
Within Ceratophrys, two clades are often recovered in phylogenies: one comprising species lacking a dorsal shield, like the Surinam horned frog (sometimes informally called the "cornuta clade", or subgenus Stombus), and another one including species usually with a dorsal shield (sometimes informally called the "aurita clade", or subgenus Ceratophrys), including the Cranwell's horned frog below (e.g. Faivovich et al. 2014; Gómez and Turazzini 2021; Barcelos et al. 2022; van der Kamp and Ortega-Andrade 2024).
References
- 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: 207–227. https://doi.org/10.2994/SAJH-D-14-00032.1
- Gómez R.O., Turazzini G.F. (2021). The fossil record and phylogeny of South American horned frogs (Anura, Ceratophryidae). Journal of Systematic Palaeontology 19: 91–130. https://doi.org/10.1080/14772019.2021.1892845
- Barcelos L.A., Almeida-Silva D., Santos C.M.D, Verdade V.K. (2022). Phylogenetic analysis of Ceratophryidae (Anura: Hyloidea) including extant and extinct species. Journal of Systematic Palaeontology 19: 1449–1466. https://doi.org/10.1080/14772019.2022.2050824
- O'Shea, M., & Maddock, S. (2024). Frogs of the World: A Guide to Every Family. Princeton University Press. The ISBN is 978-0-691-24830-1
- van der Kamp A.A.W., Ortega-Andrade H.M. (2024). Phylogeny, historical biogeography and climate niche differentiation in extant species of Ceratophryidae (Anura, Hyloidea) frogs in South America. Frontiers of Biogeography 17: e132672. https://doi.org/10.21425/fob.17.132672
- 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, 11963. doi:10.1038/s41598-017-11968-6
- Duellman W.E., Lizana M. (1994). Biology of a sit-and-wait predator, the leptodactylid frog Ceratophrys cornuta. Herpetologica 50: 51–64. https://www.jstor.org/stable/3892875
- 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, 90–105.
- Turazzini G. F. & Gómez R. O. (2023). A new old Budgett frog: an articulated skeleton of an Early Pliocene Lepidobatrachus (Anura, Ceratophryidae) from western Argentina, Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2023.2207092
Great post! And honoured to be cited! I must say I envy you a little... For as far as I have been studying these animal for quite some time.... I have only briefly seen a C. ornata alive once in my life!! As a paleontologist I must admit that I know much more about their bone anatomy than how the colour of their skin look like.... It's quite a shame....
ReplyDeletePleasure is mine! Was the frog you saw a wild specimen? They are indeed very beautiful, and especially members of 𝘊𝘦𝘳𝘢𝘵𝘰𝘱𝘩𝘳𝘺𝘴 are quite striking and intraspecifically variable in their patterns (even without considering pet trade colour morphs).
DeleteDoes the sit-and-wait strategy explain why these frogs like like they mostly consist of a big mouth, with tiny limbs? Under which circumstances does a sit-and-wait strategy pay off? I guess there must be a good chance of prey wandering by before you get too hungry...
ReplyDeleteI am asking because I once designed a sit-and-wait predator for Furaha (well, a 'hang-from-a-branch-and-wait' predator) but decided against it because I thought that the chances of getting prey would be too low.
Yeah, as stated in the article, they're quite sedentary, only coming out of their burrows during the rainy season. Sit-and-wait predators seem to encompass a great variety of different organisms, and there seems to be a fair amount of literature on the energetic costs and requirements of this strategy. See for example this https://www.sciencedirect.com/science/article/pii/S0003347223002865.
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