Footprints belonging to ancient four-legged animals have been discovered in a quarry in southeast Poland. Several tracks have been identified in the Zachelmie Quarry in the Holy Cross Mountains, documenting the existence of unknown tetrapods (animals with backbones and four limbs) that lived on earth about 397 million years ago.
Scientists have said that the fossil tracks are so detailed that even the impressions left by the animals' toes are visible. Experts say that the find means that land vertebrates appeared millions of years earlier than previously supposed.
It is suspected that the animals were crocodile-like in appearance and lived an amphibian-like existence and would have lived in a tropical muddy shoreline in the Middle Devonian Period of Earth history. The prints range in size and detail and some suggest that the animals could have been up to 8 ft. (2.4 m) long and 10 in. (26 m) wide.
According to an expert, the discovery will change beliefs about the emergence of vertebrates on land. For example, an organism called Tikaalik roseae is an animal that had features intermediate between fish and tetrapods. However, the Tiktaalik lived about 375 million years ago and although there are slightly older transition fossils, the Zachelmie Quarry tetrapods interfere with the simple timeline. This discovery pushes back the divergence between fish and the four-legged vertebrates by about 18 million years. The tracks are also ten million years older than the oldest known fossils of lobe-finned fishes called elpistostegids, which are widely considered to be transitional forms between fish and tetrapods.
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