201 million years ago
The dinosaurs were flourishing on land, and in the sea giant reptiles called ichthyosaurs had become the top predators. Then another disaster struck. We’re not sure what caused the Triassic extinction, but it killed off around 80% of species. In the aftermath, the dinosaurs became the dominant land animals and eventually reached titanic sizes. The biggest species whose mass is accurately known, Dreadnoughtus schrani, weighed about 59 tonnes.
See other: History of Life