A 100-million-year-old chase scene
In the Magway Region of central Myanmar, slabs of sandstone contain a dynamic moment from the deep past: the footprints of a two-legged carnivorous dinosaur. These tracks, known as ichnofossils, are attributed to a theropod that lived approximately 100 million years ago, during the mid-Cretaceous Period. The arrangement and spacing of the three-toed prints allow paleontologists to reconstruct the animal's movement with considerable accuracy.
The science of studying trace fossils like footprints is called ichnology. By measuring the distance between each step, known as the stride length, and using this in conjunction with the estimated hip height of the dinosaur, researchers can calculate its speed. The analysis of the Thayetmyo trackway suggests the animal was moving at a brisk 25 kilometers per hour (about 15.5 mph). This speed indicates the dinosaur was running, not walking. While other theropod tracks found globally show speeds up to 45 km/h, the Thayetmyo prints provide a clear record of a predator in motion. The shallow heel impressions and deeper toe marks are characteristic of a running gait, suggesting the dinosaur was sprinting across a wet, sandy surface that would later harden into rock.
The Cretaceous world of Myanmar
The landscape of this region during the Cretaceous was vastly different from today. It was a low-lying floodplain or coastal plain, part of a complex tectonic region near the ancient Tethys Ocean. During this period, the landmass that is now Southeast Asia was a series of island arcs and microcontinents. The sediments that preserved the footprints were likely deposited by a river system, creating the ideal soft-but-stable ground to capture the impression of the dinosaur's feet before another layer of sediment buried and protected them.
Myanmar's Cretaceous deposits have yielded other significant fossils, particularly in the form of amber from the northern Kachin State. These amber deposits, dated to around 99 million years ago, have preserved insects, plants, feathers, and even the smallest known dinosaur of the Mesozoic era, Oculudentavis khaungraae. Although the Thayetmyo tracks are trace fossils, not body fossils like those in amber, they are another type of evidence. They record the behavior of a living animal in its natural environment, showing the dynamics of a ancient ecosystem. The presence of a medium-sized running predator suggests a habitat supporting a variety of other life forms that it would have hunted.