Calumma benovskyi and the rafting Chameleons
I am on four levels of procrastination right now, procrastinating on Wikipedia projects I started because I procrastinated on other wikipedia projects.
Anyways, Calumma benovskyi is a species of chameleon named in 2020 on the basis of a almost completely preserved skull. This little guy is special for many things, one of which is the incredible preservation. That's practically the whole skull, mandible plus three neck vertebrae, which is incredible as chameleon fossils are RARE AS HELL.
As you can say its a pretty humble looking animal, an oval skull widest at the point where the frontal and parietal meat, narrow pointed snout, large eyes and a flat headcrest, all packaged into a rather small animal.
Calumma benovskyi is a member of the genus Calumma (shocker I know), which is still around today. Calumma contains over 40 species of varying shapes and sizes, some with decently big headcrests or elongated nose crests. Some examples include the Parson's chameleon (JialiangGao), Boettger's chameleon (pbertner), the globe-horned chameleon (Matthijs Kuijpers) and the blade chameleon (Emanuele Biggi).
However, what makes Calumma benovskyi so special compared to all of these is where it was found. The thing is, modern Calumma species are endemic to Madagascar. The genus is found nowhere else on earth. However, oddly enough Calumma benovskyi is from Kenya's Hiwegi Formation on Rusinga Island (Lake Victoria). Continental Africa. How did that happen?
The answer is simultaneously simple and complex. Obviously there must have been some faunal exchange between mainland Africa and Madagascar, chameleons make that obvious enough and there are other animal groups found on both landmasses (or at least have close relatives on both landmasses). For instance the iconic Aye-Aye of Madagascar has relatives on the mainland as recently as the Miocene. So it wouldn't be unusual to assume that chameleons could have originated on the mainland and only later traveled to Madagascar. This however competes with an older hypothesis that suggests that chameleons evolved on Madagascar and dispersed from there to the continent. So which is it?
Well Čerňanský and colleagues, who named Calumma benovskyi, agree with the African origin for several reasons. For one, the Kenyan species is the oldest known member of this genus. If its on the mainland during the Miocene then perhaps thats where they first evolved (tho this is hard to proof given the absence of fossils). Then there's the matter of phylogeny. Generally speaking, on a phylogenetic tree these guys are surrounded by groups from mainland Africa all around. There's some outliers, like the genus Brookesia that is believed to have arrived in Madagascar much earlier during the Paleocene and the big-nosed chameleon which turned out really weird. But in broad strokes it seems that the Madagascar groups branch away from African ones. Finally on a practical level one has to consider ocean currents. In the paper its argued that during the Oligocene and Miocene, when the second chameleon dispersal may have taken place, currents would have been directed away from the African coast and towards Madagascar. So if a chameleon were to sit on a branch that, through some events ended up in the ocean, it would be swept out towards the island. But a chameleon starting from Madagascar would have to go against the currents to reach Africa. Logically, it just makes more sense for them to have gone eastward. This only changed later during the Mid Miocene. And since Calumma benovskyi lived during the EARLY Miocene, before the shift in currents, it couldn't have come from the island. The conclusion seems simple. It is the oldest known Calumma species, most of the more basal groups are continental and currents at the time only go away from Africa. Case closed?
Weeeeeeeell not entirely. The phylogenetic analysis throw a few curveballs into that neat little package. For the time being I'll ignore the fact that the long-nosed chameleon was recovered as more basal than some African groups in some analysis, as the authors explain that this is likely just the results being fucked over by its weird head. The real problem instead lies with the specific position of Calumma benovskyi and the sister group to this genus. The later aspect concerns the genus Furcifer, another group primarily found on Madagascar (and some other islands that don't matter right now). Following the works of Tolley and colleagues, who also were among those suggesting an African origin, Furcifer is the sister group to Calumma and branched off from them during the Eocene. So if Calumma originated on the mainland, then so must have the last common ancestor between the two genera? Now that doesn't exactly overthrow the hypothesis of course. Both could have split on the mainland and separately arrived on Madagascar, not a big deal, just not as neat. Speaking of things that aren't as neat. Analysis shows that Calumma benovskyi is fairly derived. In simple terms, as far as we know its not the ancestor of the Madagascar chameleons but sits among them. Perhaps then there were multiple dispersal events in Calumma itself or perhaps this position is simply not correct. After all, if Calumma was around in continental Africa, then it seems likely that there was a much greater diversity of chameleons present, one we simply don't know from fossils. So perhaps further discoveries, new taxa, would help make sense of something that now just doesn't have all the pieces yet.
Whatever the case, the authors still hold on to the African origin and it does still make sense when considering age, currents and the surroundings. Hell, the species name itself is a reference to this hypothesis, tho the guy they named it after has a really dubious life history that puts Baron Münchhausen to shame. But I digress. Perhaps this is simply something that will make a lot more sense once we find out more.
To wrap things up, here's the only two serious paleoart pieces of this species I came across. The first published in the year of the animal's naming by Connor Ross/RajaHarimau98 and the later not too long ago by Joschua Knüppe. Because if there's an obscure animal chances are Joschua drew it.
And finally, here's the Wikipedia page that skips the theatralics and has a bit more of the anatomical stuff for those really interested. It also has all the sources and none of my struggling to make sense of the mess that is chameleons traveling across the Indian Ocean. Just the stuff from the papers. Calumma benovskyi - Wikipedia
