Complex sentence: The discoverers originally assigned the English name of the biblical monster, Leviathan, to this prehistoric whale as "Leviathan melvillei", however, the scientific name "Leviathan" was a junior homonym of "Leviathan" for the mastodon ("Mamut").
Split into simpler sentences: The discoverers originally assigned the English name of the biblical monster, Leviathan, to this prehistoric whale as "Leviathan melvillei". However, the scientific name "Leviathan" was a junior homonym of "Leviathan" for the mastodon ("Mamut").