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Footprints that alter history

15 January 2010

395-million-year-old footprints have been discovered in Poland.

Researchers at Uppsala University, working with Polish scientists, have discovered fossil footprints from land-dwelling animals that are 395 million years old. The discovery leads to the sensational conclusion that the history of land animals on earth is at least 18 million years longer than researchers previously believed.

- These findings mean that we have to revaluate a major part of the early evolutionary history of land animals, says Professor Per Ahlberg at the Department of Physiology and Developmental Biology, one of the two co-directors of the study.

For nearly eighty years, paleontologists have combed the earth looking for bones and skeletons of the earliest land vertebrates or “tetrapods” – the ancestors of all later amphibians, reptiles, birds, and mammals, including humans. Their finds have indicated that land vertebrates emerged relatively suddenly about 380 million years ago.

But there is another potential source of information about the earliest four-footed animals: their fossilized footprints. Now a Polish-Swedish research team has studied footprints at Zachelmie stone quarry in Poland that are 18 million years older than the oldest known fossil skeleton. This means that our picture of the history of land animals needs to be radically revised.

The prints show that large tetrapods, up to three meters long, lived in the marine tidewater zone about 395 million years ago. The setting is also a surprise: nearly all earlier hypotheses about the emergence of tetrapods have placed the step from water to land in freshwater environments, and tied to the evolution of land vegetation and land ecosystems.

- Instead, it now appears that our distant ancestors left the sea to feast on stranded animals left behind by the ebbing tide, says Per Ahlberg.

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