14 DAY TRIAL // A new research analyzing three sets of footprints from three different sites in the Holy Cross Mountains of central Poland, discovered the oldest evidence of the dinosaur lineage – fossilized tracks, and described them in this week's Proceedings of the Royal Society B.
The research was led by Grzegorz Niedźwiedzki of the University of Warsaw and the Polish Academy of Sciences, who has been excavating footprints from the location for nearly a decade now, in collaboration with Stephen Brusatte, a graduate student affiliated with the Division of Paleontology at the American Museum of Natural History.
The Permian–Triassic extinction event, also known as the Great Dying, occurred 251.4 million years ago, becoming the passage between the Permian and Triassic geologic periods.
This was the most serious extinction event ever as up to 96% of all marine species and 70% of terrestrial vertebrate species disappeared and it is the only known mass extinction of insects.
One or two million years after this phenomenon, an animal smaller than a domestic cat left footprints on the fine mud in today's Polish territory.
This means that the closest relative of dinosaurs on Earth lived about 250 million years ago, 5 to 9 million years earlier that what was previously thought.
This research also includes the footprints of a 246 million year old Sphingopus, as the oldest evidence of a bipedal large-bodied dinosaur.
Stephen Brusatte says that these are “the closest dinosaur cousins immediately after the worst mass extinction.
“The biggest crisis in the history of life also created one of the greatest opportunities in the history of life by emptying the landscape and making it possible for dinosaurs to evolve.”
The footprints included in this research come from three sites in the Holy Cross Mountains in Poland, all quarries being within 25 miles (40 km) away one from another.
These three sites represent three different ecosystems as they stand for different time periods: the Stryczowice trackway is the oldest at 250 million years, the Baranów trackway is the most recent at 246 million years old and the Wióry trackway is in between.
Knowing more about an animal based on its footprints is rather complicated but, fortunately, dinosaurs have a very specific walk, with their two feet being closer together than for crocodiles or lizards.
The footprints discovered in Poland show that they clearly belong to dinosaurs, with specific features like three prominent central toes and smaller outer two toes, a parallel alignment of these three digits, and a straight back edge of footprints, which is evidence of a dinosaur-like simple hinged ankle.
As all of these features were found on the oldest site, the researchers concluded that the prints found at Stryczowice are the oldest evidence of the dinosaur lineage.
But these dinosaurs are actually considered “stem dinosaurs”, the very close relatives of dinosaurs that were not part of the actual dinosaur species.
Another characteristic of this dinosaur is that it walked on four limbs, which is rather unusual for dinosaurs, even if its forelimbs began to shrink.
The other two trackways show that dinosaurs evolved: the Wióry site, with traces from 248 million years ago, shows that the tracks remained quadrupedal, while the footprints from 246-million-years-ago Baranów might be the earliest evidence of bipedal larger dinosaurs (these tracks are called Sphingopus and have 15 cm in length).
Grzegorz Niedźwiedzki says that “Poland is a new frontier for understanding the earliest evolution of dinosaurs.
“It used to be that most of the important fossils were from Argentina or the southwestern US, but in Poland we have several sites that yield footprints and bones from the oldest dinosaurs and their closest cousins, stretching throughout the entire Triassic Period.”