Oldest evidence of dinosaurs found in Polish footprints

Oct 06, 2010
The 246 million year old footprints of Sphingopus isp. from the Early Anisian of Baranów, Poland are associated with a trackway that is even more dinosaur-like in that the gait was bipedal.These tracks are the oldest record of a large-bodied (track length 15 cm) and bipedal member of the dinosaur lineage. Credit: Grzegorz Niedźwiedzki

fossilized tracks -- is described this week in Proceedings of the Royal Society B. Just one or two million years after the massive Permian-Triassic extinction, an animal smaller than a house cat walked across fine mud in what is now Poland. This fossilized trackway places the very closest relatives of dinosaurs on Earth about 250 million years ago -- 5 to 9 million years earlier than previously described fossilized skeletal material has indicated. The paper also described the 246-million-year-old Sphingopus footprints, the oldest evidence of a bipedal and large-bodied dinosaur.

"We see the closest dinosaur cousins immediately after the worst ," says Stephen Brusatte, a graduate student affiliated with the Division of at the American Museum of Natural History. "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 new paper analyzes three sets of footprints from three different sites in the Holy Cross Mountains of central Poland. The sites, all quarries within a 25-mile radius of each other, are windows into three ecosystems because they represent different times periods. The Stryczowice trackway is the oldest at 250 million years. The Baranów trackway is the most recent at 246 million years of age while the Wióry trackway is sandwiched in time between the others.

Because footprints are only an imprint of a small part of the skeleton, identification of trackmakers is often tricky. Luckily, dinosaurs have a very distinctive gait, especially when compared to their diapsid relatives (the evolutionary group that includes birds, reptiles, and extinct lineages) like crocodiles and lizards. While lizards and crocodiles have a splayed walking style, dinosaurs place their two feet closer together. The footprints at all three Polish sites show this feature as well as indisputable dinosaur-like features, including three prominent central toes and reduced outer two toes, a parallel alignment of these three digits (a bunched foot), and a straight back edge of footprints, additional evidence of a dinosaur-like simple hinged ankle.

The 250 million year old footprints of Prorotodactylus isp. from the Early Olenekian of Stryczowice, Poland show reduced digits I and V and parallel three middle digits, traits of the dinosaur-lineage. The gait, though, was quadrapedal. These are the oldest known fossils of the dinosaur lineage. Credit: Grzegorz Niedźwiedzki

Because all of these features are seen in footprints at the oldest site, Brusatte and colleagues conclude that the Stryczowice prints—which are only a few centimeters in length—are 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 Baranów and Wióry trackways show changes early in the evolutionary history of dinosaurs. Wióry at 248 million years ago shows slight diversification in the types of tracks, but all tracks remain quadrupedal. Footprints from Baranów 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."

This is a reconstruction of cat-sized stem dinosaur Prorotodactylus isp. found in Stryczowice, Poland that was a quadruped with a dinosaur-like gait and orientation of the toes. Credit: Grzegorz Niedźwiedzki

Finally, although the dinosaur group emerged soon after the Permian extinction, dinosaur-like tracks are rare in the footprint assemblages, representing only 2 percent of the prints discovered as opposed to 40 percent for crocodile-like archosaurs. Dinosaurs became more abundant tens of millions of years later.

"For the first 20 million years of dinosaur history, dinosaurs and their closest relatives were living in the shadow of their much more diverse, successful, and abundant crocodile-like cousins," says Brusatte. "The oldest were small and rare."

Explore further: Seeing dinosaur feathers in a new light

Provided by American Museum of Natural History

5 /5 (11 votes)

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kevinrtrs
1.5 / 5 (8) Oct 06, 2010
One has to ask the question since it's not clarified in the text: Just how does one go about determining the age of a footprint?
What are the assumptions made to reach a conclusion and how trustworthy is that conclusion?
To name but one obstacle here: The mud itself could contain particles that show an age of 250 million years but the footprint itself might only have occurred 1 million years ago during a heavy downpour. Just how does one distinguish one fact from the other in any reliable fashion?
Another question one might ask is how does one distinguish between an early dinosaur footprint and it's immediate forebearing cousins, the crocodile-like creatures? Or put another way, when did the dinosaur become a dinosaur and not remain a crocodile or something in-between? Are there ANY footprints of the thing-in-between? If not, why not?

jjoensuu
2.3 / 5 (7) Oct 06, 2010
The mud itself could contain particles that show an age of 250 million years


That, dear sir, is exactly the problem: that when "measuring" the age of a footprint (or of fossilized material that cannot be burned) the scientists rely on assumptions. This is because the only thing they could "measure" in this type of case is the material that the footprint is made in. And the material can of course be as old as ever.
Sazzle
5 / 5 (7) Oct 06, 2010
Both Above... Assuming the footprint was buried by a material of organic origin then one could date the layer immediatley above the footprint with a reasonably high degree of accuracy, hence obtaining a date before which the footprints must have been laid down.
otto1932
4.6 / 5 (10) Oct 06, 2010
@kevinrts
One has to wonder why a religionist would insist on disregarding facts and spreading lies in hopes of promoting their belief system to the uninformed. You should be aware that much more goes into determining the nature of tracks and the creatures that made them, than analysis of the material they occur in, and I would guess that you are, but you lie to foster 'goodness'.

Is that right? Is that what your god would want? Well sure, if he was only the expression of someones compulsive desire to lie in order to gain allies and cohorts.
GaryB
5 / 5 (3) Oct 07, 2010
How does one go about determining the age of a footprint?
... in any reliable fashion?
...
how to distinguish between an early dinosaur footprint and it's immediate forebearing cousins, the crocodile-like creatures?


Scientist have devoted 10K's of man years to all these issues and many more. The footprints are in rock that was once mud. Above may be layers of former seas with index fossils which are well dated. There may be micro-fossils that slowly turn color with heat deep in the earth etc. Chemical layers from asteroids and volcaneos also dateRead some texts in geology and paleontology.

Dinosaurs do not descend from crocodiles, as the article says, they have very different walking patterns and very different looking feet. There are no "in between" fossils simply because both has a common ancestor much further back. Such a fossil may or may not already be found ... but there is steady progress in finding such ancestor fossils.
Birger
5 / 5 (3) Oct 07, 2010
If the layer above and below the print contains volcanic ash, you can date the ash using isotopes- this is how the age of the footprints of Australopithecus was determined. The process gives the earlies and latest possible age of the footprints, with a gap in between for the time between eruptions. Other dating techniques use trace fossils in the different strata.

"Dinosaurs do not descend from crocodiles, as the article says, they have very different walking patterns and very different looking feet."

True. Dinosaurs are descended from the crocodile-like pseudosuchids, who were archosaurs, the same group of reptiles to which crocodiles belong.
By the time dinosaurs had become dinosaurs, they were considerably diferent from their crocodile "uncles".

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