"T. horridus"-"T. prorsus"-"T. brevicornus" was now thought to be the most conservative lineage, with an increase in skull size and a decrease in nasal horn size, and "T. elatus"-"T. calicornis" was defined by large brow horns and small nasal horn.
Vrsti "T. serratus" in "T. flabellatus" je postavil izven teh dveh skupin.