Research into the upper bodies of giant sauropods has put substance behind the favored explanation of how the Jurassic supported so many huge herbivores.
Today the largest land animals weigh 7.5 tonnes, and nothing of similar size co-exists with African elephants. Not only did land-dwelling dinosaurs grow to almost 100 tonnes, but many different species sometimes co-existed at the same time and location, raising the question of how they could acquire so much food. Moreover, dinosaurs existed prior to the evolution of C4 photosynthesis, which has increased the amount of food available to herbivores in tropical and subtropical environments.
A prime example of this diversity comes from the Morrison Formation, laid down in the western United States during the Late Jurassic 155-148 million years ago. More than 10 species of sauropod, including giants such as Brachiosaurus and Apatosaurus, have been identified. Just to make things more difficult, the environment in the area at the time was semi-arid.
It would certainly have helped if all these different species were not competing for the same nourishment. "In modern animal communities differences in diet such as this – termed 'dietary niche partitioning' – allow multiple similar species to co-exist by reducing competition for food,” says Professor Emily Rayfield of the University of Bristol.
While dietary niche partitioning has been suspected, there has been little evidence to support it. Now however, David Button, a Ph.D. student at the University of Bristol in England, has provided that evidence. Button applied the engineering modelling technique Finite Element Analysis to the skulls and neck vertebrae of the Camarasaurus and Diplodocus, the most common giants of the day.
In the Proceedings of the Royal Society B, Button and Rayfield show that the results support the theory that the two colossal creatures were eating different things.
"Our results show that although neither could chew, the skulls of both dinosaurs were sophisticated cropping tools. Camarasaurus had a robust skull and strong bite, which would have allowed it to feed on tough leaves and branches,” says Button. Meanwhile, the weaker bite and more delicate skull of Diplodocus would have restricted it to softer foods like ferns. However, Diplodocus could also have used its strong neck muscles to help it detach plant material through movements of the head. This indicates differences in diet between the two dinosaurs, which would have allowed them to co-exist."
Smaller sauropod species from the same formation also reveal signs of specialisation. Interestingly, many of these evolved from more general feeders, indicating that when it came to getting really large, it helped for dinosaurs to choose one food and stick to it.