We consider the phenomenon of morphological diversity of ants from the Cretaceous Burmese amber (Kachin). We propose an ethologic-ecological hypothesis that explains the features of the morphological diversity and of the ant communities of the Mesozoic and Cenozoic. It seems that some morphological features of stem formicoids allow assuming the absence of effective communication and, as a result, coordinated behaviour and collective hunting. Thus, the diversity of Cretaceous stem ants as predators represents food specialization by types of prey. Specialization in prey types leads to the division of the environment space into ecological niches between ant species. The crown groups of ants have evolved a crucial adaptation – effective communication and collective hunting (mobilization). This adaptation allowed them to move beyond the niches of specialized predators and serve of large colonies, since with developed communication the type and size of the prey are not strictly limited to the size of the ant and its jaws. Due to this, the structure of modern ant communities are formed more under the principle of hierarchy of colonies dominance (myrmecocomplex) than due to the division of ecological niches according to the type and size of prey, as in primitive Mesozoic ants.