|Photographed 04/01/2014 using Olympus E-420 DSLR with 40-150mm Zuiko lens and 1 KOOD magnifier. Chongwe, Lusaka, Zambia.|
I had originally filed it as Leptopelis bocagii; a mistake made much easier by the here almost perfectly round pupil; unlike Leptopelis, however, I'm fairly sure that in daylight, this little frog has a horizontal pupil.
It does, at a glance, resemble Leptopelis as found on the farm - it is a chubby, pale frog, active at night and not overly active, with a faint, symmetrical dorsal pattern. It is blunt-faced, rough-skinned, and - unlike our other locally common chubby, burrowing frog, Breviceps powerii - it can, at least in theory, jump.
But then there came doubt. Leptopelis bocagii, and our other Arthroleptid (Arthroleptis stenodactylus) both show rough skin on their bellies; this one, although it's not at its most visible here, has a clean, bright white belly all the way back.
Unlike L. bocagii , it also has a little, almost glandular ridge running around the corner of its mouth, giving it a decidedly disapproving expression that seems to be most commonly associated with Ranidae, and certainly seems to be absent from the Arthroleptidae. In fact, ignoring the colouring - which is in the first place very variable, and in the second place is often paler at night, especially when a frog's been taking a swim in a chlorinated pool - and noting that the pupil is, in this instance, uninformative, it's actually got very little to relate him to Leptopelis; the snout is too bulbous, the legs are too short, and the tympanum (ear) is very nearly invisible.
And finally, there was a little white protuberance on the heel of the back foot:
Which all seems to point, at least in theory, to the sand frogs (Tomopterna). The nearly invisible Tympanum - which is somewhat more visible in the first picture, where the animal's overall colour is paler - would suggest Tomopterna cryptotis, but at least two other species - T. krugerensis and T. tandyi; if this is, actually, Tomopterna at all, the call is listed as the only reliable way to separate these three; T. cryptotis is our tentative identification only because the other two have not, to my knowledge, been recorded from Zambia.
It's worth noting that they are not usually found in swimming pools; they are typically associated with rivers and temporary pools, where they bury themselves in the sand when the water retreats - the little flange on the foot is an aid to rapid burrowing. There are, however, several small streams and rivers in the wider area, some of them barely an hours walk away, which quite likely went from dry to flooded in the weeks before this little one was found.
As far as frogs are concerned, I have bypassed my commitment to freely available literature, and instead use Alan Channing's Amphibians of Central and Southern Africa; it's awesome and I really feel that more people should own it.