Our planet still has many mysteries that we are still understanding today. We found the last one in Mammoth Cave in the United States, where The longest known cave system on the planet is located and where they were ‘hiding’ two new species of prehistoric sharks. These have been trapped in the limestone rock for 325 million years, and thanks to their great state of conservation, they are allowing us to rewrite what we knew about the evolution of these predators.
A mystery. The question in this case is mandatory: how did two sharks end up in a cave system and not in an underground lake? To understand how these two species ended up in these Kentucky caves, you have to look at the geological clock.
In this way, we know that about 325-340 million years ago, during the period MississippianNorth America did not have its current configuration. The area now occupied by Mammoth Cave was submerged under a shallow tropical sea that was part of the sea route that connected to the supercontinent Pangea.
Its fossilization. When these sharks died, their bodies sank into the soft sediment of the sea, but over millions of years this sediment became the limestone that today forms the caves where they have been found.
This was in addition to the subsequent erosion that created the Mammoth Cave tunnels, which has acted as a natural excavator and exposed fossils that would otherwise have been encased in the solid rock.
Over millions of years, that sediment became the limestone that today forms the walls of the cave. The subsequent erosion, which created the Mammoth Cave tunnels, has acted as a natural excavator, exposing fossils that would otherwise be encased in the solid rock.
The protagonists. The species that have been identified belong to the order Ctenacanthus, a lineage of primitive sharks with defensive spines on their dorsal fins. Specifically we have Troglocladodus trimblei, a shark baptized thus in honor of the park guard and his troglodyte origin and whose teeth are key, suggesting that he fed on soft prey such as small fish, catching them quickly instead of crushing them.
The other protagonist is Glikmanius careforumwhich is the bone crusher. This is because it had a powerful jaw and teeth designed for cutting and crushing. In this way, it was very easy to crush bones and shells, which is why it fed on other small sharks, fish and orthocones.
The importance. This finding is undoubtedly an ‘abnormality’ for science. This is because sharks have skeletons made of cartilage and not bone. This means that the cartilage (being softer) decomposes very quickly, which is why 99% of the shark fossils we find are just teeth.
However, the tranquil and protected environment of Mammoth Cave has allowed for unusual three-dimensional preservation. Not only teeth, but also jaws, cranial cartilage and fossil fins have been found preserved in the walls and ceilings of the cave passages.
Images | David Clode
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