The fish foot
It may have been a small step for them, but it was a decisive leap for evolution: At some point towards the end of the Devonian, fish-like creatures dared their first explorations on land. Now a new representative of these pioneers has been identified that closes an important evolutionary gap.
"Nature doesn't make leaps" was already known by the German philosopher and mathematician Gottfried Wilhelm Leibniz towards the end of the 17th century. 150 years later, Charles Darwin showed that biological evolution also adheres to this principle: the blueprint of a new species does not arise from nothing, but develops from existing structures. The discovery of a fossil that lies exactly between an old and a new group of organisms is therefore one of the special moments of happiness in a paleontologist's life.
One of the most famous of these "missing links" that mediate between "Image" and new is the primeval bird Archeopteryx, which combines reptilian and bird characteristics and thus provides an idea of how reptiles are lifted into the air. No less exciting is the question of how fish learned to walk - here, too, there must have been species that mediate between fish and land vertebrates. alt="
This animal is both a fish and a tetrapod
Neil Shubin And there really was. Towards the end of the Devonian, 365 million years ago, the two genera Acanthostega and Ichthyostega presumably already took the first steps on the way to the four-footed land vertebrates, the tetrapods. Although they preferred to roam about in the water, their already well-developed legs allowed longer explorations on land.
But where did the fishy quadrupeds get their limbs that already had fingers? A fish called Panderichthys, which lived ten to twenty million years earlier, also showed the first tetrapod characteristics in the skeleton, but was still content with fins. The genus Elpistostege appeared a little later, but it was probably not able to leave the wet element either. There has been a fossil gap between the tetrapod-like fish and the fish-like tetrapods.
This gap may now be closed with Tiktaalik roseae. This is what Edward Daeschler, Neil Shubin and Farish Jenkins call the approximately 375 million year old fossil they discovered in the Canadian Arctic [1]. The researchers from Philadelphia, Chicago and Cambridge were able to salvage a total of three well-preserved specimens on the island of Ellesmere in the Nunavut Territory.
The skeleton of the more than one meter long, crocodile-like creatures already showed typical adaptations to life on land, such as a pronounced neck, which allowed the animals more freedom of movement, and a stable chest, which could probably also defy gravity on land. The three researchers paid particular attention to the pectoral fins of their fossil [2]: Tiktaalik still had to do without real fingers, but the bone structures of the fins, which already had functional shoulders, elbows and parts of the wrists, presumably allowed a first cautious step.
"Tiktaalik blurs the line between fish and land animals," Shubin points out. "This animal is both a fish and a tetrapod. We jokingly call it a fish pod."
The "fish pod" probably met a richly laid table. In the Devonian, its territory was not in the icy Arctic, but in the tropical climate on the equator and contained an amphibious landscape, similar to that of today's Amazonia. The "big shallow water fish" - as the name is translated in the language of the local Inuit - could undertake its occasional shore excursions without competition. In the later Carboniferous, the age of the amphibians, the vertebrates finally gained a foothold on land.
