Raw fish, wolf fin, and "Liao" raw fish soup: This fish shares a "circle of friends" with dinosaurs

In the primary school Chinese textbook, there is a poem called "Fish Fossils". The poet integrates his life experience into the process of a fish changing from a fresh and free life to a rigid and rigid fossil. Fish fossils are fossils that were discovered earlier by humans and have been recorded and studied more. For example, in the "Shaanxi General Records" during the Jiajing period of the Ming Dynasty, there is a record about stone fish: "Stone fish are found in Yulong, 40 miles west of Weiyang. They are found by digging the ground and breaking the rocks. They look like loaches and crucian carps, with scales and manes, and can prevent clothing moths." After field investigations by scientists, the stone fish recorded here is actually a fossil of wolffish.

Wolffish are freshwater fish that lived from the Late Jurassic to the Early Cretaceous, belonging to the class of bony fishes. There are many species of them, and their geographical distribution is also very wide, mainly distributed in eastern Asia, such as my country, North Korea, the Mongolian People’s Republic and Siberia, Russia. In my country, they are mainly distributed in the northern region, with the largest numbers in Liaoxi and Beipiao. It is one of the most widely distributed fish fossils in my country.

The size of wolffin fish is generally about ten centimeters, with a spindle-shaped body. The dorsal fin and anal fin are opposite and close to the back of the body, which is a more obvious distinguishing feature. However, compared with the morphological characteristics, many people are more curious about their strange name. What is the relationship between this small fish and wolves? In fact, this name was established by the famous German anatomist Johannes Peter Müller in 1848. In a fish fossil collected from the Trans-Baikal region of Siberia, the mouth of the fish was full of tiny conical teeth, which reminded people of the terrible mouth of a wolf. The dorsal fin and anal fin were on the back of the body, like wings. Therefore, based on these characteristics, Müller named it *Lycoptera in Latin. *lyco comes from the Greek word for "wolf", and ptera is the Greek word for "wing", which also means fin. Therefore, in early literature, it was also translated as wolffin fish.

They have tiny teeth and mainly feed on small insects or smaller creatures, but they are also delicacies of many larger predators. In order to defend against predators, they adopt a social lifestyle, just like most fish today. In addition, they live in a quiet water environment, such as the Liaoxi region of my country where volcanic activity was frequent at that time. During the intervals of volcanic activity, volcanic lakes were formed in mountain basins.

When the volcano erupted, the fierce flames left them nowhere to escape, and they were boiled alive into a pot of fish soup, and then covered by hot volcanic ash. Therefore, the wolf-fin fish fossils are not only numerous, but also mostly well preserved. Many fossil slabs show dozens of fossils, like schools of fish playing, with natural shapes and very beautiful. Sufficient fossil specimens also allow paleontologists to accurately determine the age of the fossil-bearing rock layers. In my country, the strata containing wolf-fin fish are generally defined as the late Jurassic period, and the disappearance of wolf-fin fish is used as the boundary between the Jurassic and Cretaceous periods.