Andrewsarchus
Andrewsarchus was perhaps the largest mammal land carnivore of all time, at over 6 metres long, 2.5 metres tall and over a tonne in weight. It was a Mesonychid, most closely related, somewhat surprisingly, to sheep and goats. This has led to this animal being referred to as, 'the sheep in wolves clothing'. It was a predator and scavenger, with teeth akin to those of whales. Relatives of Andrewsarchus gave rise to the Whales. It appears in Walking With Beasts.