As the largest known vertebrates to ever walk the Earth, herbivorous dinosaurs like Diplodocus needed to consume masses of plants in order to meet the high energy demands of their gigantic bodies. Their huge sizes, some up to 80 tonnes, rendered them largely immune to predation so in effect the only limiting factor to their survival was the availability and competition for valuable plant resources. Despite this competition megaherbivores in the late Jurassic displayed incredible diversity with several species co-existing in the same habitat.
Scientists have hypothesised that, based on the differing skull and tooth shapes of unearthed fossils, the co-survival of these massive animals depended on a sophisticated sharing of resources through specialisation of eating habits. In order to put the hypothesis to the test, the scientists behind this study analysed the mechanics of the skulls of Diplodocus and Camarasaurus, another megaherbivore that co-existed with Diplodocus in the Late Jurassic around 150 million years ago.
By CT scanning the skulls and performing an analysis of the bite forces each of the dinosaurs could have delivered, the team determined that they had different diets and foraging techniques. Camarasaurus was capable of exerting much larger bite forces than Dipolodocus. Its skull was stronger and, through 3D modelling, the team found that it would have had larger muscles pulling the jaw together to bite down. Camarasaurus would have been able to chomp down on a variety of hard, even woody, plant materials whilst Diplodocus, which had a smaller bite forces and less sturdy skull, would have had a more restricted diet.
Looking at the join between the neck and the skull the team found that the Diplodocus had more powerful ‘ventorflexor’ muscles than the Camarasaurus despite the latter having greater overall muscle mass in the head and neck area. The ventroflexor muscles are particularly important for flexing the neck which would have allowed Diplodicus to make the movements necessary in its long neck to strip branches of soft leaves and foliage, say the team.
Diplodocus and Camarasaurus represent either end of a broad spectrum of diverse megaherbivores say the team. Other giant herbivores that lived at the same time probably had foraging techniques which fitted somewhere in between.
The team say that such specialised foraging behaviours, called ‘dietary niche partitioning’, helps to explain the incredible diversities of these co-existing giant herbivores seen in the fossil record.