The largest beasts on Earth – Science Matters week 23

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Around 170 million years ago, sauropod dinosaurs wandered across a salty lagoon on a landmass that later became the Isle of Skye.

Their fossilised footprints were discovered by dinosaur hunters Steve Brusatte and Tom Challands from Edinburgh University in 2015.

Sauropods are the large, long-necked, herbivores including the well-known Brontosaurus and Brachiosaurus and the animals that made the footprints probably weighed 20,000kg. Eventually they evolved into the largest creatures ever known – the titanosaurs, including the aptly named Dreadnoughtus – 26 metres long and weighing more than 50,000kg – 10 times heavier than an African elephant.

Like most youngsters, dinosaurs fascinated me in primary school, but I never thought to ask how they sustained their enormous bulk. As Brusatte describes in his brilliant book*, the answer is their unique body plan.

Adult titanosaurs needed to eat around 50kg of foliage daily, a feat accomplished by the addition, and enlarging, of vertebrae to extend their distinctive necks. So, by just standing still and swinging their heads, they could consume all plants within a 26-metre-diameter circle, while expending very little energy.

But how did they manage to move around when just lifting their heads and feet appears to defy gravity? Everything is explained by adaptations to their respiratory system, which combined an energy-generating machine and an air-con system, which also helped movement.

Titanosaur lungs were connected to numerous air sacs that filled body cavities, even burrowing extensively into bones. Air sacs stored oxygen-rich air that passed through the lungs in one direction only, allowing for super-efficient oxygen extraction. What’s more, the air sacs’ huge surface area dissipated heat, so averting heat stress. And finally, by creating a honey-comb effect in bones, air sacs lightened without weakening the skeleton, thereby allowing animals to move around with ease.

If only we could have met these giants. But at least their (much smaller) close relatives are around today. Birds are dinosaurs. And with the same efficient respiration and light-weight bones they can fly far and high, even over Mount Everest.

*Steve Brusatte, Author of The Rise and Fall of the Dinosaurs (Macmillan 2018).