Fish from Moleret and Stolleklint clay
In the molar itself (Fur Formation), fossils of over 50 different species of bony fish have been found, many of which are between ½-1 meter long. These include codfish, mackerel fish, glossy fish and the elongated sea bass. There are also plenty of small fish. More than 25 species of fish are known from the slightly older Stolleklint Clay, 10-12 of which are also found in the molar.
The most common fish in the clay is a relative of modern-day Argentina (golden salmon and river herring). It is found in all stages of growth. From small juveniles no more than a few centimeters long, with the earliest ossification barely visible, to fully grown specimens of around 10 cm.
The second most common fossil fish in the molar is the smelt. The smallest are not much larger than 1½ cm long, but parts of the fish have also been found that show they could be at least ½ m long.
The third most common species in the molar is the “Polymixiid”: a primitive relative of the true spiny-finned fish. They could grow to about 40 cm long, but no tiny young have ever been found, so they must have bred elsewhere.
Among the fossils from both Stolleklint Clay and Molér, we rarely find adults and very small juveniles in the same places. Just like today, the large and small individuals of the same species ate completely different foods – and many began their larval life in the plankton as hunters of small animals and as food for larger fish – sometimes even of their own species. However, we have not observed such cannibalism in the molar, where almost all other fish seem to have eaten the small ‘golden salmon’, as far as we have been able to determine from preserved stomach contents.
Stolleklint Clay
The Stolleklint clay is completely black and a few hundred thousand years older than the molar clay. The fossils are preserved in so-called ‘shales’: thin hardened layers in the finely layered gray-black siltstone, which also contains a few volcanic ash layers – the lowest in the ‘ash series’.
The fine layering and complete lack of benthic animals and burrows shows that there was almost no oxygen in the bottom water.
