Once more, it’s time we spoke about the frogs.
Caption: a froggy montage, variously depicting (clockwise from upper left) Leptodactylus, Rhinella, Phyllobates (all hyloids) and Rana, Rana larvae… and Rana (all, err, ranoids). Images: Darren Naish.
I’ve made an effort to cover frogs a fair amount here at TetZoo, I really have, but somehow it’s just never enough. Today I want to write about a major frog clade I’ve written about a few times before but still don’t feel I’ve covered in sufficient depth. Namely… Allodapanura. Unless you’re an amphibian taxonomy or phylogeny* nerd – yes, they do exist – you likely haven’t heard of this group at all, which is perhaps odd since it’s huge, globally important and phenomenally important ecologically. And Allodapanura is not only huge, but becoming huger, since new species and genera within the group are being named at a fairly remarkable rate.
* Your regular reminder than taxonomy and phylogeny are not the same thing, and that only the taxonomic system known as PN or phylogenetic nomenclature is explicitly anchored on phylogeny.
Caption: an allodapanuran montage. 1. The gastrophrynine microhyline Gastrophryne. 2. The otophrynine microhylid Otophryne. 3. The hyperoliid Phlyctimantis. 4. The cophyline microhylid Cophyla. 5. The scaphiophrynine microhylid Scaphiophryne. 6. The squeaker Arthroleptis. 7. The pig-nosed frog Hemisus. 8. The short-headed frog Breviceps. These illustrations are among the many, many frogs I’ve drawn for my in-prep textbook (which you can support and learn about here).
For starters, let’s note here that we’re deep within the so-called advanced frog clade Neobatrachia, and thus well away from spadefoot toads, fire-bellied toads, pipids and so on. Studies on frogs mostly find Neobatrachia to consist of two major clades – hyloids (Hyloidea or Hyloides) and ranoids (Ranoidea or Ranoides) – which are conventionally distinguished on the basis of pectoral girdle anatomy (genetics distinguishes them too). And within Ranoides/Ranoidea, recent studies have supported a divergence between one clade which includes the classic, ranid frogs and all their allies (it’s termed Natatanura), and another… and that’s Allodapanura.
Caption: simplified cladogram of the frog lineages discussed in this article, the topology here mostly based on that of Frost et al. (2006) and Pyron & Wiens (2011). As usual, the illustrations here are from my in-prep textbook (which you can support here). Image: Darren Naish.
I should note that the taxonomy I’m using here – all these new(ish) names – follows the major study of amphibian phylogeny that is Frost et al. (2006). This study has been mildly controversial and criticised quite heavily by some, this criticism involving methodological issues as well as the robustness of the findings and taxonomic proposals based upon them. For all that, quite a few of their key contentions have been supported by other studies, among them the monophyly of the group we’re discussing here (Pyron & Wiens 2011): Frost et al. (2006) found the major frog group Microhylidae to be close allies of a clade of mostly African frogs grouped together as the afrobatrachians, and termed the whole lot Allodapanura (it means something like ‘otherly strange frogs’). If you’re thinking “What are microhylids?”… well, hold that thought. We’ll get to them in another article.
Caption: everyone loves Breviceps, they look so cute. This is a Bushveld rain frog B. adspersus. Image: Bernard Dupont, CC BY-SA 2.0 (original here).
Let’s look at afrobatrachians first. They’re an especially fun group of frogs and include some real oddballs, some of which are so aberrant that it’s difficult to think that they’re close kin of other taxa in the clade. I’m thinking specifically of the pig-nosed, shovel-nosed or snout-burrower frogs (properly Hemisotidae) and the short-headed or rain frogs (properly Brevicipitidae), two groups which look very different in head shape but are united on the basis of anatomical and molecular data (van der Meijden et al. 2004, Frost et al. 2006, Pyron et al. 2011, Pyron 2014). I won’t say much more about either group here because they’re covered at reasonable length in some old TetZoo articles (see links below). You’ll remember that Frost et al. (2006) liked to name clades when they recovered them, and their chosen name for the Brevicipitidae + Hemisotidae clade is a classic: it’s Xenosyneunitanura (err… zee-noh-sine-yoo-nite-ah-noo-ra), a name which means something like ‘strange bedfellow frogs’.
Caption: at left, one of my favourite x-rays. It depicts the insides of Breviceps; note how reduced the skeleton it is and how it doesn’t much match the soft-tissue outline. At right: Marbled snout-burrower Hemisus marmoratus. Images: van Dijk (2001); Ryanvanhuyssteen, CC BY-SA 4.0 (original here).
These stocky, entirely terrestrial, burrowing frogs couldn’t really be more different from the biggest and most diverse group within Afrobatrachia, namely Hyperoliidae, the so-called reed, sedge and lily frog group of sub-Saharan Africa, Madagascar and some nearby island groups. Around 230 species are recognised at the time of writing. Hyperoliids are mostly arboreal (some are terrestrial hoppers or runners, like the Kassina running or clicking frogs and Phlyctimantis African striped frogs) and tend to be long-limbed, big-eyed and with large vocal sacs which are associated with odoriferous gular glands (Starnberger et al. 2013). Yes… odoriferous gular glands: scent-producing glands which are activated when the frogs use their vocal sacs! Some of the Phlyctimantis frogs predate on other frogs and are highly toxic to humans and other mammals.
Caption: a hyperoliid montage. At left, Vlei frog, Red-legged kassina, Red-legged running frog or Spotted running frog (other common names are available!) Phlyctimantis maculatus. At right, Common reed frog Hyperolius viridiflavus of eastern Africa. Images: Dawson, CC BY-SA 2.5 (original here); Nick Hobgood, CC BY-SA 3.0 (original here).
It’s long been thought that hyperoliids are close kin of another sub-Saharan group, the squeakers (Arthroleptidae). Both have similar tadpoles and their hand skeletons are alike. Frost et al. (2006) called the Hyperoliidae + Arthroleptidae clade Laurentobatrachia, the Laurent here being Belgian herpetologist Raymond L. Laurent (1917-2005), well known for his numerous works on South American and central African amphibians and reptiles. Squeakers are diverse enough that it’s hard to generalise about them: there are small, forest-floor, leaf litter frogs, climbers, and burrowers among the group. They’re conventionally split into three subfamilies (Arthroleptinae, Astylosterninae and Leptopelinae), which have sometimes been regarded as separate families. The remarkable Hairy frog Trichobatrachus robustus of western Africa belongs here, specifically within the astylosternines where it’s surrounded by mid-sized, big-headed species which have big eyes and vertical pupils.
Caption: Fantastic 19th century illustration of male Trichobatrachus by J. Green. Image from here, in public domain.
Incidentally… when reading about these amazing, diverse, neat amphibians, you might often find yourself thinking “I wonder how those animals are faring in these times of climate change, habitat loss, escalating pollution, increasing human encroachment and so on?”. Yeah, I wonder about that too. In many cases, the data which might allow us to determine the answer to that question isn’t necessarily there. But in other cases it kinda is… aaand the news isn’t great. Tropical African frogs of some species – though not all – have dramatically declined within recent years (Hirschfeld et al. 2016).
Squeakers have been celebrated in the popular science press thanks to new discoveries made about the remarkable ‘claws’ present in the Hairy frog and various other members of the group. These aren’t really claws at all, but the hook-shaped distal phalanges of the respective digits which burst from their digital tips when needed (Barej et al. 2010).
Caption: Claws visible on the hindfeet of (a) Astylosternus, (b) Trichobatrachus and (c) Scotobleps, from Barej et al. (2010). Scale bar = 5 mm.
I have to end things there for now (boy, is time tight these days). More allodapanuran frogs soon, plus other stuff. For previous TetZoo articles on frogs, some specifically on the groups mentioned here, see…
In pursuit of Romanian frogs (part II: WESTERN PALAEARCTIC WATER FROGS!!), July 2011
In pursuit of Romanian frogs (part III: brown frogs), August 2011
A Brief Introduction to Reed, Sedge and Lily Frogs, January 2015
'Strange bedfellow frogs' (part II): pig-nosed or shovel-nosed frogs, or snout-burrowers, February 2015
The Remarkably Weird Skeletons of Frogs, December 2016
A Love Letter to the Common Frog, August 2020
Refs - -
Barej, M. F., Böhme, W., Perry, S. F., Wagner, P. & Schmitz, A. 2010. The hairy frog, a curly fighter? - A novel hypothesis on the function of hairs and claw-like terminal phalanges, including their biological and systematic significance (Anura: Arthroleptidae: Trichobatrachus). Revue Suisse de Zoologie 117: 243-263.
Pyron, R. A. 2014. Biogeographic analysis reveals ancient continental vicariance and recent oceanic dispersal in amphibians. Systematic Biology 63, 779-797.
Starnberger, I., Poth, D., Peram, P. S., Schulz, S., Vences, M., Knudsen, J., Barej, M. F., Rödel, M.-O., Walzl, M. & Hödl, W. 2013. Take time to smell the frogs: vocal sac glands of reed frogs (Anura: Hyperoliidae) contain species-specific chemical cocktails. Biological Journal of the Linnean Society 110, 828-838.
van der Meijden, A., Vences, M. & Meyer, A. 2004. Novel phylogenetic relationships of the enigmatic brevicipitine and scaphiophrynine toads as revealed by sequences from the nuclear Rag-1 gene. Proceedings of the Royal Society of London B 271, S378–S381.
van Dijk, D. E. 2001. Osteology of the ranoid burrowing African anurans Breviceps and Hemisus. African Zoology 36, 137-141.
