Compare: Late Carboniferous temnospondyls were not very convincing as
> (semi)terrestrial apex predators by today's standards. But if you > take the whole ecosystem into account, quite a lot of them seem to > have been just that....if you consider the Late Carboniferous dissorophoids "quite a lot of" contemporary temnospondyls, then yes. I can only think of *Amphibamus*, *Eoscopus*, *Mordex* and *Fedexia* off the top of my head, all of them quite small. *Dendrerpeton*, also small, is said to have a canal for the lateral-line organ in the ventralmost row of dorsal scales; that organ is useless in air, and dries out and dies when exposed to air unless it's covered by skin thick enough to make it useless. (See footnote.) *Capetus* and *Iberospondylus* may have visited dry land on occasion, or not -- they're only known from skulls. What others are you thinking of? Large adult ghost-lineage eryopids?
The terrestrial apex predator may actually have been *Arthropleura*. I'll provide a reference later.
Footnote: Aquatic lissamphibians retain the lateral-line organ. Those that become semiaquatic or terrestrial at metamorphosis lose the organ during that event. In the eastern North American newt *Notophthalmus viridescens*, it sinks deeper into the skin instead; when the terrestrial juvenile phase (2 years, IIRC) is over and the "red eft" turns green (viridescens = "becoming green"), it comes back out, and the aquatic adult phase begins. I can provide a reference for this, too.