Largest Prehistoric Organisms

Basilosaurus was once recognized as one of the largest known extinct cetaceans at 18 metres (59 ft) in length.

The largest fossil Odontocete ("toothed whale") was the Miocene physeteroid whale Livyatan melvillei which was estimated to be 13, 5-17, 5 meter in length. One notable feature of L. melvillei was its teeth which were 36 cm long and is unmatched by any other animal extinct or alive.

The largest monotreme (egg-laying) mammal ever was the extinct long-beaked echidna species Zaglossus hacketti, known from a couple of bones found in Western Australia. It was the size of a sheep, weighing probably up to 100 kg (220 lb).

The largest extinct marsupial was Diprotodon, about 3 m long (10 ft), standing two meters (6 ft) tall and weighing up to 2,786 kg (6,142 pounds). The two largest carnivorous marsupials were the Marsupial Lion and Thylacosmilus (larger than the Tasmanian Tiger), both about 6 ft long (1.8 m) and weighing 100–160 kilograms (220–350 lb). The largest kangaroo ever was Procoptodon, which could grow to 3.0 m (10 ft) and weigh 230 kilograms (510 lb).

Read more about all such prehistoric organisms.