This is the Irish Elk and its one of the largest deer that ever lived. It stood at around 7ft tall at the shoulders and large specimens weighed up to 700kg (1,500lbs) or more. It lived in Ireland and across Europe and went extinct in the early Holocene due to nutrient stress and human hunting for their huge antlers which could reach a size of 40 kg (88 lbs) and span almost 10 ft.
The Short-Faced Bear is widely regarded as the largest mammilian carnivore to have ever lived. The average bear weighed in at around 900 kg (1,950 lbs) with some large specimens weighing over 1,000 kilos. On its hind legs it stood at over 9-10 ft tall while the shoulder height while walking on all fours was estimated to be around 6 ft. Despite its size, it was known as the "running bear" as its long limbs allowed it to run at 30-40 mph enabling it to run down large deer species in a 'cheetah-like' fashion.
The Haast Eagle is the largest eagle to have ever lived, weighing in at 15 kg (33 lbs) which may not sound like much but when you consider the largest living eagle (Australian wedge-tail) weighs on average 3-4 kilos it gives you a sense of scale. The eagle preyed specifically on large flightless birds that could weigh up to 500kg (1,100 lbs) and went extinct after human settlers killed and ate all of their prey around 1400.
The Megalodon was the largest shark species to have ever lived. At roughly 3-4 times larger than todays largest shark species, the great white, Megalodon patrolled the oceans as the top predator. Weighing around 50 tons and with a length of 18-20 meters, the Megalodon was too large for its own good and went extinct around 2 million years ago when dwindling prey and a cooling ocean caused the shark to starve, unable to regulate temperature around its large body.
Gigantopithecus, ancient Greek for Giant Ape, was the largest ape to have ever lived standing up to 10 ft and weighing up to 540 kg (1,190 lb). Despite its intimidating size, Gigantopithecus ate a diet of tough fibrous roots and stalks as well as fruit and nuts similar to that of pandas and orangutans. Some have suggested that this ape was bipedal like modern humans due to the skulls position on the sine. Gigantopithecus may have become extinct approximately 100,000 years ago because the climate change during the Pleistocene era changed the plants from forest to savanna causing a shortage of food. Some have theorized that this ape was the root of the 'bigfoot' myth as many hominids were around before the time of extinction.
The title of the largest cat in history goes to the Siberian tiger. You may have thought that Smilodon (Saber-toothed tiger) would take this spot but it's a common misconception. Smilodon was built very robustly and was stocky and muscular but was, in fact, smaller than today's Siberian tiger - the largest of which was a captive tiger named Jaipur who weighed 464 kg (1,025 lbs) whereas Smildon rarely, if ever, exceeded 400 kg. (I excluded the Liger from consideration as its not found naturally in nature. **PART 1 CORRECTIONS** - Quite a few people stated that the Siberian tiger was in fact not the largest felid ever, through further research the American lion, Barbary lion and Eurasian Cave lion all weigh around 400 kilos - similar to that of the largest Siberian tiger. Any one of these could've been given the title of the largest. - I mentioned that the great white was the largest modern shark when of course it is the whale shark.