One of the main reasons paleontologists still know woefully little about ancient living things is the complete decay of their soft tissues over time. For creatures with a skeleton or shell, this is not so bad, but creatures such as worms disappear completely. Therefore, to study the species Pennichnus formosae, scientists had to examine their burrows, which remained at the bottom of the ancient seas.
319 of these objects were studied before scientists concluded that some of them belonged to the former dwellings of worms. The main evidence was the abundance of iron in the upper part of the curved tunnel - traces of the vital activity of bacteria. They fed on sticky mucus, which the worms secreted to strengthen the sandy walls. This is a characteristic feature - some prey resisted so desperately that it led to the destruction of the hole entrance. It constantly had to be strengthened, hence the unprecedented concentration of traces of bacteria in the form of iron.
Most likely, the Pennichnus formosae worm was the distant ancestor of the current predatory worm Bobbitt Eunice aphroditois (known as the purple Australian worm - ed. Techcult). But it only reached more than 2 m in length, although it was only 2-3 cm in diameter.However, the terrible grasping jaws with curved mandibles compensated for the lack of mass - the worm quickly jumped out of ambush and dragged everything that swam past into the hole. Scientists suggest that this "hellish worm" had no natural enemies, but it literally colonized vast areas of the southern seas of Eurasia.