Thaindian News

London, Jan 9 (IANS) Our ancestors left the water at least 18 million years earlier than previously thought, suggests the discovery of fossil footprints in Poland.
These results force us to reconsider our whole picture of the transition from fish to land animals, says Per Ahlberg of Uppsala University, Sweden, one of the two co-authors of a new study on the subject.

For nearly 80 years, palaeontologists have been scouring the planet for fossil bones and skeletons of the earliest land vertebrates or “tetrapods” - the ultimate progenitors of all later amphibians, reptiles, birds and mammals, including ourselves.

Their discoveries have suggested that the first tetrapods evolved relatively rapidly from lobe-finned fishes, through a short-lived intermediate stage represented by “elpistostegids” such as Tiktaalik, about 380 million years ago.

But there is another potential source of information about the earliest tetrapods: the fossilised footprints they left behind.

The Polish-Swedish team which conducted the research describe a rich and securely dated footprint locality from Zachelmie Quarry (Poland) that pushes back the origin of tetrapods a full 18 million years beyond the earliest skeletal evidence and forces a dramatic reassessment of the transition from water to land.

The trackways show that large tetrapods, up to three metres in length, inhabited the marine intertidal zone during the early Middle Devonian some 395 million years ago, says an Uppasala University release.

This means that not only tetrapods but also elpistostegids originated much earlier than we thought, because the position of elpistostegids as evolutionary precursors of tetrapods are not in doubt and so they must have existed at least as long, says Per Ahlberg.

These results were published online this week in Nature.