Myrmecia (Bull ants), as well as Harpegnathos and some other ponerine ants are called dinosaur ants because they appear very primitive compared to other ant genuses.
They only have a very limited degree of individual specialization (workers are all about the same size and there's no big difference between queen and workers, also often the workers can mate and produce fertile eggs), a low degree of organisation (workers hunt alone or in small packs, they rarely ever use pheromone trails but have phenomenal eyesight and are quite smart), don't form large colonies (they usually max out at a few hundred in the wild) and usually are very big ants (Harpeganthos is about 3.5cm).