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Twelve years ago I published my first paper, describing a new species of frog from the genus Rhombophryne from northern Madagascar—the product of an extracurricular project I was able to pursue with Frank Glaw at the Zoologische Staatssammlung München whilst I started my Master’s at the Ludwig-Maximilian University of Munich. By the time it was published, I had already begun work on several more descriptions of related species of diamond frogs that were published over the subsequent years. But in the background, I had also started to work on a monographic treatment of the genus as a whole: a total revision of all Rhombophryne species that would include not just taxonomic revision, but also a compendium of practically every published mention of these unusual little frogs from Madagascar that I could get my hands on, as well as new data from personal examination of almost every specimen of these frogs in Europe, and a key to the species. Twelve years after starting work on this project, I am proud to announce the publication of the 126-page monograph (not including dozens of pages of supplementary tables), with revised treatments of all existing species and the description of seven new species! The study is coauthored by numerous wonderful colleagues who have joined me in this endeavour and contributed enormously to its successful publication. The paper is published Open Access in Vertebrate Zoology.
What twelve years of work has revealed is that these frogs are a lot more diverse than we had thought, both in terms of species number and in terms of morphological appearance. In 2013, when I started work on them, we had a vague idea that the morphospace spanned from the rather strongly built Rhombophryne laevipes to the gracile R. minuta to the pancake-shaped R. testudo, and there were 10 species known. Following the publication of this monograph, there are now 27 species described, and our understanding of Rhombophryne morphospace is a lot more comprehensive: there are six species groups, and the group is now known to consist of multiple highly fossorial lineages, a miniaturised lineage, numerous small round detriticolous species, and a host of rather gracile species. What is more, I wanted to emphasise in this monograph especially the known unknowns: there are at least three candidate species, and several interesting specimens without genetic data that we report upon that will doubtless further expand the species list of the genus. I am sure that the total tally will exceed 30 species, not least because several of the species described were discovered on very recent expeditions, and further fieldwork is practically guaranteed to yield more new species to describe.
Allow me to introduce each of the seven new species we have just described:
Rhombophryne maraorao
A little burrowing species from the northeast of Madagascar that is very similar ecologically to R. coudreaui. The name maraorao means ‘rough to the touch’ in Malagasy, referring to the rough skin of this species. They do a weird thing where they straighten all of their limbs and go stiff in self defence,
Rhombophryne mavokely
A little detriticolous species from the northeast of Madagascar that resembles R. mangabensis and R. savaka but has more bumps on its skin. The name mavokely is the Malagasy word for ‘pink’ but literally translates as ‘small yellow’. This species is small and sometimes pink and sometimes yellowish, so the name seemed extremely apt. This species was the first Rhombophryne I ever saw alive—I caught the first ever specimen immediately underneath my hammock on Marojejy in 2016!
Rhombophryne sonaliae
A rather well known species from eastern Madagascar that has previously been called R. alluaudi—until we showed in 2019 that the correct use of that name was for a Plethodontohyla alluaudi from southern Madagascar! We dedicated this species to Sonali Garg, in recognition of her fantastic work on frogs over the years.
Rhombophryne anatiala
A very poorly known species very closely related to R. sonaliae but found further north and differing subtly. The name anatiala means ‘in the forest’ in Malagasy, referring to the forest habitat of these frogs.
Rhombophryne kotrobaratra
An interesting species from northeastern Madagascar with rather unusual anatomy, especially its quite long and strong hindlimbs. The name kotrobaratra means ‘thunder and lightning’ in Malagasy, and refers to the inclement weather that seems to bring these frogs out.
Rhombophryne quentini
An orange-thighed species from high-elevation forests in northern Madagascar that resembles R. ellae. I named R. ellae after my partner, Ella, and I thus took particularly great pleasure in naming this new, closely related species after my son, Quentin. A little family of frogs.
Rhombophryne kilonjy
A small, poorly known and obscure species related to R. ellae and R. quentini but found in lowland forest close to the coast in northwestern Madagascar. The name kilonjy means ‘pebble’ in Malagasy, and refers to the pebble-like appearance of this curious little frog.
A monograph like this reveals just as much about what is known as what is not known about the biology of the species it concerns. For example, I tried whenever possible to include relevant natural history data and especially dietary information from specimens that I was permitted to dissect. These data are fragmentary, but yield valuable insights. Only one specimen examined so far had a gastropod in its stomach. Others have ants, beetles, spiders, myriapods, and even one terrestrial amphipod, in their guts. Interestingly, micro-CT revealed that the gut of one group of particularly subterranean species seem to consist almost exclusively of soil, and this has led me to speculate that these species may be truly fossorial (i.e. feeding underground), and possibly even partly geophagous—or otherwise just terrible at catching their food. But these are just vague impressions cobbled together from isolated individuals; for the majority of species, we know almost nothing of their ecology, and absolutely nothing of their diet. Beyond these basics, it gets even murkier: we know practically nothing of their locomotion; their social interactions; behaviour; their habits in the dry season.
A monograph like this is kind of status report, not a final report. The status is: we know 27 species well enough to give them names, and several more species that, in the years ahead, we will hopefully get to know well enough to name as well. We have cursory glances at how the species differ morphologically, genetically, and even bioacoustically, but there are very big and now rather well characterised gaps in our knowledge, which we can work to fill. I hope that soon we will have a high-resolution, dated phylogenomic tree of these frogs that will allow us to better understand how they evolved, and the pressures that shaped them into the charming little jewels they are today.
The full citation is
Scherz, M.D., Glaw, F., Petzold, A., Andreone, F., Köhler, J., Raselimanana, A.P., Hutter, C.R., Belluardo, F., Rakotoarison, A., Hofreiter, M., Vences, M. & Crottini, A. (2026) A wealth of riches: a comprehensive revision of diamond frogs, genus Rhombophryne Boettger, 1880 (Microhylidae: Cophylinae), with the description of seven new species. Vertebrate Zoology, 76:485–610. DOI: 10.3897/vz.76.e172567
Madagascar never ceases to amaze me. Thanks for the update.