The world's first "gar" is in Yunnan? The ancestor of the water's little tyrant has been discovered

The gar, which now lives in the freshwater environment of North America, lived with dinosaurs as early as the Cretaceous period 100 million years ago. Although the dinosaurs became extinct, this gar has survived to this day, and research on its origin and evolution has long attracted attention.

The latest news from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences said that Researcher Xu Guanghui of the institute and Dr. Ma Xinying of Qujing Normal University recently discovered a new ancient fish fossil in the Middle Triassic marine strata about 244 million years ago in Luoping County, Qujing City, Yunnan Province. The fossil was named "Roundtail Diandongichthys", which represents the oldest and most primitive articulated-tooth fish in the world and provides important fossil evidence for revealing the origin of gar fish. The relevant research results were recently published in the "Acta Linneanis Zoologica Sinica" published by Oxford University in the UK.

Researcher Xu Guanghui said that in taxonomy, gars and their ancestral types (such as Hemivertebrates and Archichthyes) are collectively called arthropods, which constitute one of the three major groups of neopterygians in the subclass Actinopterygii.

A total of 13 fossils of the round-tailed diandongichthys were discovered in this study. It is a small long-fusiform fish with a semi-round tail and covered with shiny black square scales. The largest individual is only 5 cm long, representing the smallest toothed fish in the Luoping Biota. Chronostratigraphic studies have determined that the Luoping Biota is about 244 million years old, so the round-tailed diandongichthys also represents one of the oldest toothed fish in the world.

Previously, all the toothed fishes found in the Luoping Biota were classified into the order Archeopterygii, but the unique skeletal morphology of the roundtailed dinostegius clearly distinguishes it from the fishes of the order Archeopterygii. Based on detailed skeletal morphology, this study included the roundtailed dinostegius in a large-scale branch analysis, and the results showed that the roundtailed dinostegius was at the bottom of the toothed fishes.

Xu Guanghui pointed out that this shows that the roundtail diandong fish is more primitive than the previously discovered archfishes and all the toothed fishes in Europe and America, and represents the most primitive ancestral type of the evolutionary branch of the living eel fish. "In layman's terms, the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences has caught the world's first eel fish."

He introduced that the living gar are large carnivorous fish with an adult body length of up to 3 meters. The main reasons why it can become a "living fossil" of the dinosaur era include: first, the gar has a layer of unusually hard diamond-shaped scales all over its body to defend against enemies; second, the gar eggs are highly toxic and inedible, thus ensuring the survival of offspring; third, the gar's swim bladder also has a respiratory function, and when there is a lack of oxygen in the water, it can swim to the surface of the water to breathe.

The origin and early evolution of articulated-tooth fishes is one of the important topics of the Mesozoic fish research team of the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences. The team's research in recent years has shown that the origin of articulated-tooth fishes is earlier than that of dinosaurs. Dinosaurs first appeared in the Late Triassic, while the oldest articulated-tooth fishes appeared in the Luoping Biota in the early Middle Triassic in China, represented by the Archichthys and the newly discovered round-tailed diandongichthys.