Dinosaurs were big. Blue whales are bigger. This extinct marine mammal might have been bigger still
Tyrannosaurus rex
, a meat-eater, was up to 12 metres long—about half the length of a tennis court—and is thought to have weighed up to 7 tonnes. Some of the herbivorous dinosaurs were bigger still:But the true giants do not live on land, where the pull of gravity imposes limits on how heavy an animal can grow. They live in the sea, where their enormous bodies can be supported by the water. The most massive animal to have ever lived is still swimming around today.
Or at least, that is the upper estimate. Dr Bianucci and his team, working in the Ica Valley, an arid desert in southern Peru, were able to recover only an incomplete skeleton, consisting of 13 vertebrae and four ribs. Working out exactly how much flesh was once attached to those bones is not easy. Using skeleton-to-body-mass ratios from existing marine mammals, the researchers arrived at a lower estimate of 85 tonnes, and a central figure of 180 tonnes.
Exactly why the animal was so big is unclear. To be sure, size has its advantages. Temperature control is one. Mammals must keep their body temperatures within a tight range. As they grow bigger, their surface area rises more slowly than their volume. That means bigger creatures have an easier time staying warm in the comparatively cold ocean.
But there are downsides, too. The most obvious is that a bigger body has a bigger appetite which is harder to satisfy. Biologists believe that whales attained their modern proportions only about 5m years ago, when climatic changes produced the rich feeding conditions necessary to support their enormous bodies. SinceWorking out how an extinct animal lived is even harder than deciding just how big it was. But there are clues. One striking feature of’s bones is their density.
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