Dinosaurs have captured people’s imaginations more than any other ancient creature. These reptiles – some large, some small; some carnivores and other herbivores—rose and dominated the world’s landscape for more than 135 million years during a period known as the Mesozoic.
Today, dinosaur fossils can be found in many parts of the world, embedded in rocks. This is a series of layers or rock units in chronological order. South Africa and Lesotho’s main Karoo Basin, for example, contain abundant dinosaur fossils in rocks that formed between 220 million and 183 million years ago during the Late Triassic-Early Jurassic period. These remains include body fossils (bones) and trace fossils, which are markings in the old sediments in the form of footprints and burrows in the ground.
Body fossils can help recreate the ancient life forms, understand what they looked like, their size and even how they grew and evolved. The problem is that intact body fossils can be rare in some areas. Bone fragments alone cannot help researchers piece together the puzzle of ancient life. The traces of animals offer another avenue of study.
In the Karoo Basin, bone fossils of carnivorous dinosaurs called theropods are incredibly rare. But their footprints, preserved in the rocks of the Middle Triassic and Early Jurassic, are abundant. These fossil footprints are a treasure trove of information. They can reveal which organism made the tracks – different animals have different footprint shapes. They provide clues to the creature’s behavior – jumping on two legs will leave a different footprint than walking on four. They also provide evidence about the substrate conditions when the creature walked, such as whether it sank into wet sand or stood firmly on dry gravel.
In a recent study, our team looked at about 200 footprints attributed to theropods over a span of about 35 million years. We wanted to understand how the dinosaurs’ feet changed over time in southern Africa. The time interval we studied is critical in the history of dinosaurs because it captures a mass extinction and the subsequent recovery period of the ancient ecosystems.
Our findings reveal that over time our local theropods grew larger and had a greater diversity than the body fossil might suggest.
Footprints: a closer inspection
To begin our study, we first looked for diagnostic clues to distinguish the theropod footprints from those of other ancient animals. Theropod footprints usually preserve three, slender toe impressions where the footprint is longer than it is wide. Read also : Ford uses new high-tech stamping technology in Silverton. The middle toe has a pronounced protrusion. These footprints also often preserve violent claw marks.
We know the shape of their feet and how they moved from reconstructions based on fossil material from the theropod bodies. Scientists have also learned about these aspects of dinosaurs by making modern footprints using their closest living relatives: birds.
Once we identified the theropod footprints in the field, we quantified their footprint shape by measuring a set of standard parameters agreed upon by the global dinosaur track fossil research community. Based on these measurements across time and space, we were able to draw conclusions about the evolution of theropod foot and body size. This is possible because there is a direct correlation between foot length, and therefore footprint length, and body size (especially hip heights and body lengths).
Our study recorded a 40% increase in maximum and average footprint length in the studied time interval of 35 million years. Furthermore, we observed that larger-bodied theropods were present, although rare, in the Late Triassic and that they became even larger and more common in the Early Jurassic, during the recovery period after the mass extinction.
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These observations reflect trends recorded elsewhere in the world. We also observed that over time, theropod footprints became more widespread. This may indicate that the predator population thrived during the recovery period. However, this change in abundance may also have been influenced by changes in the ancient environment from meandering rivers with lushly vegetated floodplains to shallower ephemeral streams and lakes under dryland conditions. This newer setting is more favorable for preserving footprints because deposits in the soil are less likely to erode.
More to explore
Based on our measurements, we identified three different types of footprint shapes attributable to the three different theropods that roamed the landscape in the Early Jurassic. This means that the southern African theropod footprint record reflects a greater diversity of theropods than the meager carnivorous dinosaur body, which preserves only fragmentary material from two theropods, Dracovenator and Megapnosaurus.
Another key finding centered on changes in the shape of theropod footprints. One is that the forward projection of the middle toes (how much further forward it is than the two outermost toes) decreased over time. On the same subject : Do Christians Really Have the Power to Heal? Here’s what Science says. Another change is that small local theropods had shorter metatarsals than their contemporary North American equivalents.
These observations require more research to better understand what these changes mean, especially because the metatarsal projection has been linked to an animal’s running ability.
