Temporal and palaeoenvironmental distribution of manus- and pes-dominated sauropod trackways
Fossil tracks are a source of information about extinct animals that can supplement the osteological record, yet they are often overlooked in macroevolutionary studies. The substrates in which tracks are preserved are indicative of palaeoenvironment and habitat, and track morphology can be linked to the motion and loading of the limb. Sauropod dinosaurs represent the largest terrestrial animals ever to have existed, and the evolution of their body plan had direct consequences for their locomotion and subsequent morphology of their tracks. Here we show that the relative proportions of manus- and pes-dominated sauropod trackways appears to remain constant in the Jurassic and Cretaceous despite an apparent evolutionary anterior shift of centre of mass seen in the body fossil record. However, in Cretaceous rocks, manus-dominated tracks are most commonly recorded in cohesive substrates (e.g. mudstones), whereas pes-dominated tracks tend to be restricted to non-cohesive substrates (e.g. sandstones). This bias is not present in the Jurassic, and therefore may be the result of niche partitioning among sauropods associated with the Cretaceous diversification of the anatomically and environmentally specialized titanosaurs. In this respect, the ichnological record appears to provide complementary evidence to the osteological record and suggests a causative link between locomotion, ecology, and macroevolution in sauropod dinosaurs.