Imperial mammoth. Illustration and photo-reconstruction of two Mammoths walking in an American prairie in search of vegetation. The imperial mammoth is one of the largest known mammoth species in the fossil record, and possibly not only the largest mammoth but the largest terrestrial mammal currently known from North America. The imperial mammoth is still eclipsed in terms of size by some other mammoths; however its exact species is not certain. The imperial mammoth does seem to have suffered the same fate as the Columbian mammoth however, by succumbing to the combined effects of climate change and human hunting.