Perucetus
(Perucetus colossus)

Discovered in Peru and formally described in 2023, Perucetus is one of the most extraordinary prehistoric finds in recent memory. Its bones are extraordinarily dense — filled in with solid bone both internally and with extra growth on the outside — each vertebra alone weighing as much as 100 kilograms, acting as ballast for a slow-moving, shallow coastal lifestyle.

Its diet remains a complete mystery — no skull or teeth have ever been found, leaving scientists to speculate between shellfish, seafloor scavenging, and filter feeding as possibilities.

When first described, its estimated mass briefly gave it a serious claim to the title of heaviest animal ever, with initial estimates ranging as high as 340 tonnes. A 2024 reanalysis revised this down to around 60-70 tonnes — still enormous, but no longer the undisputed record holder.