Fossil tracks created in the Early Triassic period remain nearly perfectly preserved over hundreds of millions of years, to our present day. The excellent condition of many of these features have puzzled scientists, uncertain of how the fossils survived intact to our modern age.
Swim tracks were formed by marine reptiles traveling through water, The tetrapods, four-footed vertebrate animals who lived on land, passed through water bodies from time to time, either floating or buoyed up by the aquatic environment. The animals spent a significant amount of time on muddy deltas, as they foraged for food and mates.
These tracks are plentiful, and although it is easy to understand how the tracks were formed, paleontologists and geologists are uncertain why the markings remained so well-preserved today.
University of California, Riverside researchers believe the answer to that mystery could be due to a combination of reasons. These include swimming behavior of the animals, the environment in which the tracks were laid, and slow ecological recovery during that ancient period.
The Early Triassic period lasted from 252 to 247 million years ago. This era was one segment of the Triassic Period, marked at each end by mass extinctions around the globe. The Triassic period began immediately following the greatest extinction in the history of the Earth. A slow recovery of the biological world from this event is seen lasting throughout the period.
Geological conditions in many parts of the world could have also assisted in the preservation of the tracks.
"During the Early Triassic, sediment mixing by animals living within the substrate was minimal. This strongly contributed to the widespread production of firm-ground substrates that are ideal for recording and preserving trace fossils like swim tracks," a doctoral student at UC Davis, said.
Because there were so few animals alive during the Early Triassic, the tracks were rarely disturbed as they hardened. Periodic flooding brought coarse, grainy material into the tracks, helping to preserve the features for hundreds of millions of years.
These three conditions, put together, appear to have created a Goldilocks scenario, allowing the tracks to stay intact as they were slowly preserved.
Fossil swim tracks provide a wealth of information for paleontologists and biologists studying animals in that distant era. By examining the features, researchers can learn about tetrapods, including detailing their means of locomotion. The ancient environment also reveals itself in the fossil tracks, providing geologists with details from the ancient past.
Research into swim tracks from the Early Triassic, and how they were so well preserved was detailed in the journal Geology.
