Good point. I didn't mean to imply that the only arboreal Mesozoic
> mammals were therians. The gliding _Volaticotherium (lately regarded > as a eutriconodont) was also arboreal, and _Argentoconodon_ (a > putative close relative) might also have been an arboreal glider. The > synapsid _Suminia_ is inferred to have been arboreal much earlier > (Late Permian).Of all these (plus *Ichthyoconodon*, known from teeth similar to *Argentoconodon* and the teeth of *Volaticotherium*), only the arboreality of *Henkelotherium* seems to be homologous to that of Theria. I should also have mentioned Spalacotheroidea, likewise thought to have been arboreal and in the same general region of the tree.