Huge and long-necked, Barosaurus also had a lengthy tail which it wielded as a weapon against enemies. It lived in herds, which was also useful for defence against predators. Like all members of the sauropod group, it had one large, curved claw on the inner toe of its front foot.
This species is known from five partial skeletons from the Morrison Formation, three of them in Dinosaur Natural Monument in Utah, USA. The African species, until recently known as Gigantosaurus, was part of the Tendaguru fauna, and known from four skeletons. The rearing skeleton of Barosaurus in the American Museum of Natural History, at a height of 15m, is the tallest mounted skeleton in the world, only made possible by modern techniques of producing casts of fossil bones in lightweight materials.
Name: Barosaurus, meaning ‘slow heavy reptile’
Size: up to 27m long
Food: plants and leaves
Lived: about 150-140 million years ago in the Jurassic Period in western North America
The bones in Barosaurus’ long neck were hollow and light, which meant it could lift its head to feed quite easily. If its neck bones had been solid, it would have been too heavy to lift. Barosaurus is very much like Diplodocus – indeed the limb bones are indistinguishable between the two genera – but its tail bones are shorter and its neck bones at least one-third longer, one of which is 1m long. The two genera were in fact about the same size overall. It was longer than Apatosaurus, but its skeleton was less robust.
The way that Barosaurus and the other diplodocids were balanced at the hips suggested that they could rear up on their hind legs for feeding or for scaring off predators.
Barosaurus was once thought to have held its head like a giraffe. In order to pump blood up to the brain – a height of around 12m, 10m above the heart – the heart would have had to have weighed about 1.5 tonnes. The larger a heart, the slower it beats. A 1.5 tonne heart would beat so slowly that the blood would run back down the neck before the next beat. In fact, the length of the neck has led some palaeontologists to suggest that there were several hearts along its length, to enable the blood to reach the brain when it was feeding from high trees.
However, a recent theory was postulated that, like a giraffe, it had arterial valves in its neck. These operate in response to differentials in fluid pressure, allowing the blood to be pumped up the neck but preventing most of it from falling back down. More recent computer modelling of diplodocids like Barosaurus has shown that they probably habitually held their necks more or less horizontally, thus restricting the problem to whether the animal reared up on its hind legs or not.