January 7, 2010 – Original Source: Times, UK
A reappraisal of ancient footprints discovered in Poland suggests that creatures emerged on to land from the sea much earlier than previously thought.
The tracks, believed to be the oldest footprints ever discovered, date to 395 million years ago, long before the emergence of dinosaurs. They are likely to have been left by a large crocodile-like creature.
Previously the earliest evidence for fully walking four-legged creatures, known as tetrapods, dated to 360 million years ago. The “fishapod” fossil Tiktaalik, the skeleton of which shows both fish and amphibian features, dates to about 375 million years ago.
“This is a spectacular finding,” said Phillipe Janvier, a palaeontologist at the National Museum of Natural History in Paris. “When I saw it, I was reminded of the first footprint of man on the Moon in 1969.”
Tetrapods were thought to have rapidly evolved from fish via an intermediate stage, such as Tiktaalik, which had a tetrapod-like head and body shape but retained many fish characteristics such as paired fins instead of paws.
The latest findings, published in the journal Nature, show that fish must have begun to morph into land-dwellers much earlier than assumed and that the transformation was much slower.
The tracks suggest that they were left by a 2.5m (8ft) creature resembling a stout crocodile. However, unlike the modern-day crocodile, the ancient creature appears to have held its body up from the ground as there is no trace of it being dragged along. It may have been closer to a dog in terms of posture.
The tracks are in the Holy Cross Mountains in southeastern Poland, which 395 million years ago was a coastal region. Their discovery in rocks that teemed with marine fossils suggests that the first amphibians came out of the sea rather than freshwater marshes as had been widely assumed.
The tracks were first spotted in 2004 by the geologist Zbigniew Zlonkiewicz. Unaware of the age of the rocks at the site, he attributed them to dinosaurs.
It was not until the tracks were re-examined by palaeontologists at Warsaw University that it became clear that they were not dinosaur tracks but belonged to some of the earliest tetrapods. Simultaneously, the husband and wife team of Katarzyna and Marek Narkiewicz published work dating the age of the quarry by examining microscopic fossils embedded in the rocks.
“It was very exciting when we realised how the two pieces of work fitted together and that what we were looking at were the oldest-known footprints,” said Marek Narkiewicz, of the Polish Geological Institute in Warsaw.
While the sea of the Middle Devonian age housed a vigorous ecosystem, including fish, scorpions and crabs, the land by contrast was relatively barren. It is not clear why fish emerged from the water but one possibility is the incentive to escape competition. “It may have been easier for some fish to come out of the water and eat their prey peacefully by the shore where they wouldn’t get hassled,” Dr Janvier said.
The tracks appear to have been left by a number of different-sized individuals, although it is not clear whether these belonged to different species or simply to adult and juvenile creatures.