Because all of these features are seen in footprints at the oldest site, Brusatte and colleagues conclude that the Stryczowice printswhich are only a few centimeters in lengthare the oldest evidence of the dinosaur lineage. These dinosaurs, though, are considered "stem dinosaurs," or the immediate relatives of dinosaurs not part of the slightly more derived clade that technically defines dinosaurs. Also, this animal did walk on all four limbs, an abnormal posture for early dinosaurs and their close relatives, although it appears that its forelimbs were already being reduced to more dinosaur-like proportions since the footprints overstep handprints.
The Baranw and Wiry trackways show changes early in the evolutionary history of dinosaurs. Wiry at 248� million years ago shows slight diversification in the types of tracks, but all tracks remain quadrupedal. Footprints from Baranw at 246 million years ago, however, may be the earliest evidence of moderately large-bodied and bipedal true dinosaurs. These tracks, which are called Sphingopus, are 15 centimeters long.
"Poland is a new frontier for understanding the earliest evolution of dinosaurs," says Grzegorz Niedźwiedzki of the University of Warsaw and the Polish Academy of Sciences, who led the project and has been excavating footprints from the three sites for nearly a decade. "It used to be that most of the important fossils were from Argentina or the southwestern U.S., 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."
Finally, although t
|Contact: Kristin Elise Phillips|
American Museum of Natural History