haʊˈɛvɚ, ˈædəmztɹˈɛsmən nˈaɪntiːnhˈʌndɹɪd ˈeɪɾi sˈɛvən, jˈuːzɪŋ lˈɪnɪɹ mˌɔːɹfoʊmˈɛtɹɪks, kʊd ˈoʊnli dɪstˈɪŋɡwɪʃ bᵻtwˌiːn ðə tˈuː skˈʌl ɡɹˈuːps, sˌoʊ ʃiː fˈaʊnd ðɛɹ təbi tˈuː spˈiːsiːz fɹʌmðɪ ˈɑːksfɚd klˈeɪ, ˈɛm. sˌuːpɚsˈɪlɪˌɑːsəs ænd ˈɛm. bɹˈækɪrhˌɪntʃəs.
However, Adams-Tresman (1987), using linear morphometrics, could only distinguish between the two skull groups, so she found there to be two species from the Oxford Clay, M. superciliosus and M. brachyrhynchus.