Humans hunt the largest animals and drive them to extinction. We have always done so. The first homo sapiens lived with some amazing larger-than-life megafauna that may still be alive today if we weren’t such a murderous species. An appreciation thread for these real-life titans:
Megatherium: 6m (20ft) giant sloth weighing up to 4 tons. Like modern sloths, they slowly lumbered through the jungle. They could probably walk on two legs. Fossils have cut marks, indicating overlap with early humans. Extinct around 8,500 BC (first homo sapiens ~300,000 BC). 
Glyptodon: 1.5m (5ft) armadillo. This bad boy was around the size of a Volkswagen Beetle. While herbivorous, their heavy armor and bony tail helped in fights with conspecifics and defense against predators. Extinction around 10,000 BC at the end of the Pleistocene Epoch.
Palaeoloxodon antiquus: up to 5m (16ft) and 23 tons, the undisputed king of the elephants. Arguably the heaviest mammal to ever walk the earth, alongside Paraceratherium (“near-horn beast”): a hornless rhino. Extinct around 30,000 BC.
Phorusrhacid (i.e. “terror bird”): up to 3m (10ft) tall and carnivorous. They could run very fast in a straight line, some around 50 km/h (30 mph). Not so good at turning corners. Extinct around 90,000 BC.
Gigantopithecus: 3m (10ft) ape, herbivorous. King Louie in the 2016 Jungle Book film was one, and their closest living ancestor is the orangutan. Extinct around 100,000 BC, and no, Bigfoot is not a Gigantopithecus who decided to stick around. (Image from Jungle Book.)
Archaeoindris: 1.5m (5ft) lemur, about the size of a modern gorilla. Slow-moving, probably diurnal, primarily tree-dwelling, and exquisitely adorable. They were the largest primates in Madagascar until their extinction around 400 BC.
Mammoth: up to 3.3m (11ft), the size of a modern elephant but with thick fur and larger tusks. Two similar megafauna were woolly rhinoceroses and mastodons. In 2015, the company Geltor started making real mastodon gelatin using bioengineering! Extinct around 2,000 to 10,000 BC.
Smilodon (i.e. “sabre-tooth tiger”): 1.2m (4ft) tall with canine teeth up to 20cm (8in), 5cm longer than T-rex teeth. A new skull finding in 2020 suggests some smilodons were 1.5-2x larger than expected, up to 436kg (891lbs)! Extinct around 10,000 BC. tandfonline.com/doi/full/10.10…
Teratornis incredibilis (i.e. “incredible monster bird”): wingspan up to 5.5 m (18 ft). Few fossils have been found, but there are other condor-like Teratorns. As the last ice age ended, prey scarcity and human hunting may have led to their extinction also around 10,000 BC.
Moa bird: up to 3m (10ft) tall, 250 kg (550 lbs). Moas were the only wingless (not just flightless) birds and the largest animals in New Zealand until extinction ~1440 AD, 200 years after humans arrived. Before humans they survived in NZ for 2.5 million years, if not much longer.
Arctodus (i.e. "short-faced bear"): up to 3.4m (11ft) and 1,600 kg (3,500 lbs). That's around 1.5x the size of a grizzly. Probably more carnivorous than modern bears, prey included the bison, muskox, deer, and ground sloths! Extinct around 9,000 BC.
Megaloceros giganteus (i.e. "giant deer" or "Irish elk"): up to 2m (7ft) tall with the largest antlers of any animal at 3.6m (12ft) across. Could these massive mantles be used for fighting? A 2019 study argues yes, based on computer modeling of the impact. royalsocietypublishing.org/doi/pdf/10.109…
Castoroides (i.e. "giant beaver"): around 2.5m (8 ft) long with incisors up to 5cm (6 in) long. Not close relatives of actual, modern beavers, and no evidence of dam-building. Their bulk made it hard to travel long distances, which may have contributed to extinction ~8,800 BC.
That's it for now! Sources were primarily Google Images, Brittanica, and Prehistoric Wildlife. I read original scholarly publications when encyclopedias were ambiguous or seemed unrealiable. Feel free to reply here or DM if any sources are not easily found. Thanks for reading.
