Uppsala expedition to Greenland makes spectacular fossil discovery

Here is the whole team at the excavation site. From left: Alex Chavanne, Grzegorz Niedzwiedzki, Per Ahlberg, Henning Blom, Martin Qvarnström and John Marshall.

Following an exceptionally successful scientific expedition to Greenland, more than 200 kg of fossil material is on its way back to Uppsala. "The discoveries will revolutionize our understanding of the early evolution of land vertebrates" says Per Ahlberg, Professor of evolutionary Organismal Biology and leader of the expedition.

A team from the Department of Organismal Biology at Uppsala University, financed by a grant from the European Research Council, recently returned from a month-long expedition to the mountains of Greenland, where they had been collecting fossils of so-called 'four-legged fishes' – the first backboned animals to leave the water, nearly 400 million years ago. Their efforts were crowned with triumphant success.

"It's absolutely incredible" says Per 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."

Tetrapods evolved from fishes

The aim of the expedition was to explore an important, but almost unknown, time interval in the history of land vertebrates: the transition between the Devonian and Carboniferous periods, which coincided with a major mass extinction. It has long been known that backboned land animals (also known as tetrapods, "the four-footed ones", in other words animals with legs instead of paired fins) evolved from fishes during the Devonian period, which lasted from 419 to 359 million years ago.

The very first Devonian tetrapod fossils were discovered in Greenland during the 1930s, by Swedish-Danish expeditions led by scientists from the Swedish Museum of Natural History in Stockholm. They became known as 'four-legged fishes' because they retained some fish-like characteristics such as a tail fin. The first to be discovered was given the name Ichthyostega. After that, progress was slow: until this year, scientists had discovered and named four different Devonian tetrapods from Greenland.

Tetrapods become "invisible" for a while

All these four-legged fishes from Greenland come from the later part of the Devonian, but not from its very end. The same is true for the rest of the world: only a single tetrapod is known from end-Devonian rocks.

"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.

Does this mean that their evolution received a 'push' from the mass extinction at the Devonian-Carboniferous boundary? Researchers have not been able to answer that question, because they haven't known what tetrapods were like immediately before the extinction event. But that's about to change.

Fossils from four or five tetrapods

A thousand metres above sea level, on the flank of Mount Celsius on Ymer Island off the east coast of Greenland, the expedition discovered an exceptionally rich deposit of tetrapod fossils. It comes from the end of the Devonian, about 1-2 million years after the time of Ichthyostega, and appears to contain at least four or five different tetrapods. All, except maybe one, are unknown to science. In other words, the results from a single summer have approximately doubled the number of tetrapods discovered in Greenland during the previous 90 years.

Some of the new tetrapods appear to be classic four-legged fishes, but others look more advanced. In other words, it looks like the evolution of a more modern tetrapod fauna had begun already before the mass extinction at the Devonian-Carboniferous Boundary.

Creating an overview of the environment

In addition to the skeletons the expedition also discovered coprolites (fossil excrement), footprints and body impression of tetrapods. Fossils of clubmoss trees and fern-like plants, fragments of a scorpion-like arthropod, and environmental data from the sediments themselves contribute to creating an overview of the subtropical environment where the tetrapods lived.

Now, more than 200 kg of fossil material is on the way to Uppsala. Then will follow several years of research on the fossils, largely on the basis of synchrotron microtomography (three-dimensional x-ray imaging) which will be carried out at the ESRF synchrotron in France.

"We will be opening the door to a lost world" says Per Ahlberg.