\Bron`to*the"ri*um\, n. [NL., fr. Gr. ? thunder +
? beast.] (Paleon.)
A genus of large extinct mammals from the miocene strata of
western North America. They were allied to the rhinoceros,
but the skull bears a pair of powerful horn cores in front of
the orbits, and the fore feet were four-toed. See
Illustration in Appendix.