Dinosaurs have captured people’s imagination ever since their bones and teeth were first scientifically described in 1822 by geologist and palaeontologist Gideon Mantell in England.
Dinosaur bones have taught us a great deal about these animals from the “age of dinosaurs”, the Mesozoic Era, which stretched from approximately 252 million years ago to 65 million years ago. However, there’s something especially appealing about a different kind of dinosaur fossil: their tracks, which show researchers what the animals were doing while they were alive.
Ichnology is the study of tracks and traces and, since 2008, the Cape South Coast Ichnology Project has documented more than 370 vertebrate tracksites on South Africa’s southern coast. These sites are from the Pleistocene Epoch, which stretched from approximately 2.6 million years ago to 11,700 years ago, much more recent than the Mesozoic.
We knew that this coastline contained Mesozoic sedimentary rocks, some of which include non-marine sediments that could potentially preserve dinosaur tracks. We are both familiar with dinosaur tracks from our research in Canada, so we decided to investigate the possibility of tracks in South Africa’s Western Cape.
We found some – and, once we knew what to look for, it was evident that the tracks were not rare. In a new paper published in the journal Ichnos, we describe our findings in detail, presenting evidence of tracks of sauropods (enormous plant-eating dinosaurs) and possibly ornithopods (another group of large herbivorous dinosaurs).
The tracks were found in a rugged, remote, breathtakingly spectacular coastal setting. They were made by dinosaurs in a variety of estuarine settings. Some were walking on sandy, inter-tidal channel bars. Others walked on the bottom of tidal channels, their feet sinking down into soft mud forming the bed of the channel. Other vague “squishy” structures were formed by dinosaurs wading, or even wallowing in the muddy fill of abandoned channels.
These tracks are around 140 million years old, from the very beginning of the Cretaceous period when the African and South American tectonic plates were starting to pull apart. Southern Africa has an extensive record of Mesozoic vertebrate fossils, but that record ends at around 180 million years ago in the Early Jurassic with the eruption of voluminous lava flows. To the best of our knowledge, all the southern African dinosaur tracks known until now are from the Triassic and Jurassic periods, so they pre-date these eruptions.
That means these tracks are not only the first from the Western Cape. They also appear to be the youngest – that is, the most recent – thus far reported from southern Africa.
Knowing where to look
After deciding to hunt for potential dinosaur tracks, we visited a few likely sites on the Cape south coast in 2022, choosing areas with non-marine deposits of the appropriate age, mostly in the eastern coastal portion of the Western Cape. We found a few promising spots on that visit and, in 2023, undertook a dedicated examination.
Large horizontal bedding surface exposures in this area are very rare. We knew that, if we were to find dinosaur tracks, they would be evident mostly in profile in vertical cliff exposures.
In the public imagination a dinosaur trackway extends across a level surface and toe impressions are visible. Some may also know that the infill of dinosaur tracks can occur on what are today the ceilings of overhangs or cave roofs. However, there are also distinctive features that allow tracks to be identified in profile. That’s because the animals’ footfalls deformed underlying layers in a distinctive manner.
The problem is that other mechanisms, such as earthquakes, are capable of generating broadly similar deformation structures.
The deposits we were examining had probably also been affected by seismic activity. The challenge was for us to differentiate between the two types of deformation.
The Early Cretaceous rocks that we examined had been studied and reported on decades ago, and the deformation structures had been attributed to origins such as earthquakes rather than living organisms. Since then, however, scientists have developed a better appreciation of what dinosaur tracks look like in profile.
After careful examination, our conclusion was straightforward: both dinosaur-generated and earthquake-generated types of deformation were present in the Cretaceous rocks.
Further evidence that we were looking at dinosaur tracks comes from the region’s bone fossil record. Cretaceous bone material has been reported from the region, mostly in the Kirkwood area in the Eastern Cape province. Two dinosaur bones have also been reported from the Knysna area in the Western Cape. One of these, a theropod tooth, was found – and correctly identified – by a 13-year-old boy.
Clearly, dinosaurs were present in the Western Cape area. That means our discovery of ichnological evidence of their presence is not entirely surprising, but it is still extremely exciting.
Keep exploring
Our team plans to keep exploring deposits of suitable age in the region for evidence of more dinosaur tracks. We also hope that our discovery will inspire a new generation of dinosaur trackers to continue the quest and keep exploring.
This article first appeared in The Conversation