How resilient are sharks? They have survived several mass extinction events

Fossils are like masterpieces of nature, not only beautiful in their own right, but also of great scientific research value. However, not all organisms can form fossils. For example, sharks are a type of vertebrate that are difficult to leave fossil records. Most sharks only have teeth or marks left after their bodies decay, and very few of their body structures can be preserved.

Shark Teeth

But there is an ancient primitive shark. Although there are not many complete fossil records, its richness is far beyond the reach of other sharks. Not only are there a large number of tooth fossils, but also scales, dorsal fins, and even fecal fossils. This is the Hybodon.

The bow shark belongs to the class Chondrichthyes, subclass Elasmobranchs. It appeared in the Carboniferous period and flourished in marine freshwater areas and river areas around the world from the Permian to the Cretaceous period. It is an intermediate transitional species in the evolution of sharks. They are about 2 meters long, which is not outstanding in the Mesozoic era or even in modern oceans. But they are very good at "surviving". Not only did they survive the brutal Permian extinction, but in the early Triassic period, they once became the strongest in the ocean. At that time, many young marine reptiles were on their menu. Even after the Carnian flood event (230 million years ago, a million-year rainy season caused by excessive carbon dioxide emissions) and the Triassic extinction, they are still active.

Hybodon fossil

This is due to their lack of specialization and wide adaptability, which can be seen from their teeth: the teeth of the hybodids are two rows, the front row is sharp and sharp, suitable for preying on fish or slippery guys such as squid, and the back row of teeth is flatter, used to crush shelled mollusks, allowing them to eat anywhere. In the Jurassic period, the hybodids still maintained a high diversity and were distributed in many freshwater areas around the world, but in the late Cretaceous period, perhaps because of the threat of large predators, perhaps because of strong competition from new cartilaginous fish, or perhaps both, they completely became extinct and became a "relief" carved in the rock strata.

Restoration of the bow shark

Sharks are generally difficult to fossilize, mainly because they are cartilaginous fish and their bones are not easy to preserve. Compared with other sharks, the hybodont has cartilage tissue that is closer to hard bones, enamel scales, and hard dorsal fin spines. In addition, they are distributed all over the world, making them the members with the richest fossil records among sharks. If they could speak, they might proudly say, "No one knows how to be a 'relief' better than me."

The above is what we shared in this issue. See you next time if you are interested.