Robber prey drama in a prehistoric lake

Unique insights into a 290 million year old food chain

Reconstruction of the predator-prey scenario in the submerged Humberg lake. The food chain encompasses the three levels of consumers attested by the fossil record: Acanthodier (1st level), temnospondyle amphibian larvae (2nd level) and Triodus (3rd level). © Humboldt University Berlin
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The drama occurred about 290 million years ago: a predatory amphibian larva chased and ate a small bone fish, only to be devoured by a thorn shark. Witness to this food chain have now become German paleontologists. Because they discovered the skeleton of the small shark including Amphibienlarve and bone fish in a rock plate in the Saarland.

The discovery of the fossil barbed shark with preserved digestive remains provides unique and comprehensive insights into a primeval food chain in a lake for the first time. Jürgen Kriwet, Florian Witzmann and Stefanie Klug from the Museum of Natural History in Berlin and Ulrich Heidtke from the Palatinate Museum in Bad Dürkheim are now giving insights into this 290 million year old food chain in the journal "Proceedings of the Royal Society".

The fossil represents the first and oldest direct evidence of a three-level food chain and shows that sharks also ate amphibians. Thus, this ecosystem is, to this day, the only one of the geological history from which this prey preference is known. This conserved vivacious predator-prey scenario took place in the so-called "Humberg Lake" of the Saar-Nahe Basin. The spiny sharks are considered to be the oldest sharks that had adapted to freshwater conditions about 300 million years ago. At the end of the Triassic, about 200 million years ago, these ancient sharks disappeared and were replaced by modern sharks.

Shark as a top predator in a freshwater lake

All living things in an ecosystem are related to each other. These dependencies can be illustrated by food webs. At the base of such a food chain are always producers who do not feed themselves on other living beings, but serve other organisms, the consumers, as food. In general, four so-called trophic levels are realized in lakes, the first being those of the producers. Hierarchically, three consumer levels are built on top of that. At the end of the food chain, crocodiles or predatory bony fish such as pike or largemouth bass are found in modern lakes.

Prickly shark Triodus sessilis with digestive remains. (a) Photo of the fossil from the Permian of Lebach (Southwest Germany). (b) Drawing of the eaten temnospondyl amphibian larvae. Left: an almost complete skeleton of the species Cheliderpeton latirostre with remains of a digested juvenile Acanthodier. Right: the skull of Archegosaurus decheni. HU Berlin

For the first time, fossilized prawn shark from the Perm, with its fossilized remains of food, provides a direct glimpse of the oldest known food chain, reflecting vertebrate relationships at a time when neither modern bony fish nor crocodiles existed, but S water sharks and large amphibians dominated aquatic ecosystems. display

J rgen Kriwet and his co-authors compared the information derived from these fossils with those on food webs and chains from geologically recent periods. They found that the food web in the last stage of development of Humberg Lake was very complex and thus stable cological conditions were established in the lower Permian.

Freshwater sharks had to give way to amphibians

This fossil triplet also illustrates that over time, predator-prey relationships in continental aquatic ecosystems have changed dramatically and that macroevolutionary mechanisms have played a significant role in these changes. While in the Palozoic era spiny sharks and amphibians were at the bottom of the food chain, sharks disappeared after the extinction event at the Permian / Triassic border and played no role in continental ecosystems.

The resulting ecologic gaps were filled with Pal ozoic amphibians for another 50 million years, until they too were displaced by the emerging crocodiles at the end of the Mesozoic. The niche of the spiny sharks was occupied successively by the first appearing in the Mesozoic modern bony fish (Teleosteer). The events at the end of the Triassic, which led to the largest extinction event in the history of the earth, thus had a lasting effect on and changed continental ecosystems.

(Humboldt University Berlin, 06.11.2007 - NPO)