Fossil finds in East Greenland shed light on tetrapod evolution | Polarjournal
There are probably still countless paleontological treasures buried in the rock layers of East Greenland. Professor Per Ahlberg’s research team discovered such treasures as fossil remains of lycopods (right) and especially of four-legged terrestrial vertebrates (left) during their expedition, opening a door to the evolution of terrestrial vertebrates and their environment more than 360 million years ago. Images: Grzegorz Niedzwiedzki, courtesy of Uppsala University.

That today’s terrestrial vertebrates, including us humans, evolved from aquatic ancestors is a fact. It is also a fact that corresponding evidence comes from finds made in Greenland almost 80 years ago. But for a long time these findings remained the only ones and left a big gap in the evolutionary history of the first land vertebrate. That may have changed now that a research group has collected over 200 kilos of fossil material in East Greenland.

Remains of probably four to five different and still mostly unknown four-legged land vertebrates, so-called tetrapods, have been discovered by the six-member research team led by Professor Per Ahlberg, an expert at Uppsala University. Further, numerous plant remains, scorpion-like arthropods, ferns, and even fossil feces were added, providing clues to the habitat in which the animals had lived and their evolution. A total of more than 200 kilograms of fossils were collected by the scientists during their expedition, which was supported by Polar expedition guide Alex Chavanne. “It’s absolutely incredible,” says Professor Ahlberg. “We found more and better material than we could ever have hoped for. This will revolutionize our understanding of the early evolution of land vertebrates.”

“The fossils date to the very end of the Devonian period, 359 million years ago,” states Per Ahlberg to PolarJournal. “This is is an important time in the evolutionary history of terrestrial vertebrates (or tetrapods, as they are also known). Finds of fossil trackways from Poland and Ireland show that previously aquatic vertebrates had started to make the transition onto land during the Middle Devonian, 393 to 383 million years ago. From the Late Devonian of Greenland, in strata that are just a little older than those that the expedition explored this year, researchers have found near-complete fossils of the tetrapods Ichthyostega and Acanthostega. These animals combine fish-like and terrestrial characteristics, giving a snapshot of the evolutionary transition.”

But how animals had evolved at the end of the Devonian and the beginning of the Carboniferous remained a big question mark for a long time. For fossils were hardly found. “This is kind of unfortunate, because something really interesting happens right at the Devonian-Carboniferous boundary: many fish groups go extinct and the tetrapods become almost ‘invisible’ for a while, with very few fossils. When they become visible again, some way into the Carboniferous, they are much more advanced,” explains Per Ahlberg. At that time, about 50 percent of marine animal species became extinct in two mass extinctions. He now hopes the findings will shed light on the darkness and show how terrestrial vertebrates had evolved before extinction at the Devonian-Carboniferous boundary.

The researchers achieved this success on Ymer Island in East Greenland. This island with its mountain Mount Celsius, situated between the two large fjord systems Keiser-Franz-Joseph- and Kong-Oscar-Fjords, has been the site of tetrapod fossils in the past. From the 1930s to the 1950s, several fossils of Ichthyostega, a genus of animals long thought to be a link between fish and terrestrial vertebrates, were discovered here. However, recent analyses show that the evolution from aquatic to terrestrial vertebrates was more complex and that the previously known classification of genera needs to be revised.

The finds made by the scientists under sometimes very icy and difficult conditions should definitely contribute to this. For the next few years, researchers will definitely be busy evaluating the fossils. And meanwhile, numerous other fossils await discovery in the rock layers of Mount Celsius. Since they have been waiting hundreds of millions of years to be discovered, the time until their eventual discovery should seem like the blink of an eye.

Dr Michael Wenger, PolarJournal

Contributed image: skull fragment, image: Grzegorz Niedzwiedzki, courtesy of Uppsala University.

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