A 2003 study of thirty species ( by Sean Brady of Cornell University ) shows that the ecitonine and doryline army ants evolved from one group in the mid-Cretaceous period in Gondwana , and so the two subfamilies are now one called Ecitoninae , but not everyone says this . A 2003 study of thirty species ( by Sean Brady of Cornell University ) indicates that the ecitonine and doryline army ants together formed a monophyletic group : all shared identical genetic markers that suggest a common ancestor . Brady concluded that these two groups are therefore a single lineage that evolved in the mid-Cretaceous period in Gondwana , and so the two subfamilies are now generally united into a single subfamily Ecitoninae , though this is still not universally recognized .