Sauropods were long-necked, plant-eating dinosaurs that started off relatively small. However, after 20 million years of evolution, they grew to enormous proportions. Naturalist David Attenborough compares the thighbone of an early sauropod to the largest ever found.
The first sauropods to appear on earth were comparatively small creatures.
This is the cast of the thigh bone of one of them.
It's not even as big as my thigh bone.
But after about 20 million years, some had become pretty big.
This is a thigh bone from one of those creatures.
But then after that, our giant appeared.
This is its thigh bone.
It's the largest ever found.