Tetrapod footprints dating back 397 million years have been discovered in the Świętokrzyskie mountains in southern Poland in what was, at the time they were made, a seashore. All previous fossil evidence for these earliest known four-limbed vertebrates has been found in river deltas and lakes.A bit later:
"Our discovery suggests that the current scientific consensus is mistaken not only about when the first tetrapods evolved, but also about where they evolved," says Grzegorz Niedźwiedzki of the Department of Palaeobiology and Evolution at the University of Warsaw in Poland, who discovered the footprints in 2002 in an old quarry near the town of Kielce.
"It was assumed that tetrapods evolved in river deltas and lakes, partly because all previous fossil evidence has been found in these environments," says Jenny Clack, curator of vertebrate palaeontology at the University Museum of Zoology in Cambridge, UK. "This research suggests that the first tetrapods that crawled onto land were, in fact, living in shallow seas."The link to the Nature article appears to be free (for the moment). The article authors write:
Until now, the replacement of elpistostegids [animals like Tiktaalik and Panderichthys] by tetrapods in the body-fossil record during the mid–late Frasnian has appeared to reflect an evolutionary event, with the elpistostegids as a short-lived ‘transitional grade’ between fish and tetrapod morphotypes (Fig. 5a). In fact, tetrapods and elpistostegids coexisted for at least 10 million years (Fig. 5b). This implies that the elpistostegid morphology was not a brief transitional stage, but a stable adaptive position in its own right. It is reminiscent of the lengthy coexistence of non-volant but feathered and ‘winged’ theropod dinosaurs with volant stem-group birds during the Mesozoic.One of the most exciting areas in palaeontology right now is the origin of the tetrapods. As with most scientific discoveries, this will answer a bunch of questions and pose even more.
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