Researchers conducting excavations in the 安i皻okrzyskie Mountains in central Poland, one of the oldest mountain ranges in Europe, have discovered footprints and fossils of the earliest four-footed terrestrial animals.

The research findings are published in a January issue of the international science magazine Nature. Many scientists say the discovery may mean that paleontology textbooks will have to be revised.

In 2002, during excavations in a disused quarry at Zache軛ie near the city of Kielce, 安i皻okrzyskie province, two Ph.D. paleobiology students, Grzegorz Nied德iedzki of the University of Warsaw and Piotr Szrek of the Polish Geological Institute, discovered unusual footprints with digits. Initially, both were unaware of the significance of their finds. But when they decided to write about the footprints to Prof. Per Erik Ahlberg of Uppsala University, he immediately replied to tell the young Polish researchers they had made a sensational discovery, one that might change several well-established paleontological theories. The seven-year research studies conducted by a Polish-Swedish team proved that the footprints had been left by tetrapods, the earliest four-legged vertebrates. The fossils and footprints discovered in the quarry are around 18 million years older than the remains of animals regarded until recently as the earliest tetrapods. They come from the Devonian period and date back at least 395 million years.

"The importance of the discovery is that these are very old trackways left by animals with four legs and toes in sediments of a shallow sea and its shore," said Nied德iedzki, one of the authors of the article published in Nature.

Until recently, paleontologists across the world adhered to a theory that tetrapods evolved from fish through an intermediate form called elpistostegids, a group of lobe-finned fish. Elpistostegids had many body features typical of fish, for example fins instead of limbs, but their heads resembled the heads of tetrapods. Elpistostegid fossils were found in the arctic part of Canada in 2006. Prof. Marek Narkiewicz of the Polish Geological Institute, the Polish head of the research project and another author of the article, says the latest discovery has disproved the theory that elpistostegids were the ancestors of tetrapods. It turns out that the latter appeared earlier than elpistostegids. The fossils found in 安i皻okrzyskie Mountains are 10 million years older than the earliest elpistostegid fossils known by science.

Narkiewicz says the research also provides a new insight into the environment in which tetrapods developed. "These were not swamps, coastal forests, or inland waters, as was believed until recently, but a large shallow marine body of water located far from land and drying out periodically," he says.

What are now the 安i皻okrzyskie Mountains were a shallow extensive lagoon 395 million years ago. The trackways show that the animals started to colonize land directly from the sea. This challenges the theory that marine animals first adapted to freshwater life and only then started walking on land.

The footprints are up to 26 centimeters wide, suggesting that the animal was at least 200-250 centimeters long. This, in turn, disproves the theory that the animals that first started walking on land were small and only later evolved into larger creatures.

The trackways suggest that the animal strode in shallow water while leaping on land. The researchers found no evidence of a dragging body or tail, which proves that the animal was sure-footed. This disproves the theory that the earliest terrestrial vertebrates had poorly developed limbs and dragged their body along the ground. Amphibians, reptiles, birds and mammals are all descended from the earliest tetrapods. The footprints found in 安i皻okrzyskie Mountains belong to predatory animals that probably had lungs although they may have also had vestigial gills at the same time .

The discovery may considerably change our perception of the theory of evolution. Nature writes that, although the evolutionary transition from fish to terrestrial four-legged animals seemed to be well documented by science, it may now be necessary to rewrite the history of tetrapod evolution.

The discovery has been used to promote the 安i皻okrzyskie region among both Polish and foreign visitors. Since mid-January a reconstruction of the tetrapod from 安i皻okrzyskie Mountains has been displayed in the "Jurassic park" of the Museum of the Earth in Solec Kujawski. A new logo of the 安i皻okrzyski Archeo-Geological Trail will also allude to the tetrapod. The Regional Tourist Organization wants to promote the province under a new slogan suggesting that 安i皻okrzyskie is the cradle of life.