In 2004, the American paleontologist Neil Shubin found an ancient animal fossil in the Arctic Circle, he was surprised to find that this fish actually grew two "arms", after identification, this strange fish lived in the Devonian Period 380 million years ago, nearly 200 million years earlier than the dinosaurs, the Devonian Period was originally the "age of fish", so it was not surprising to find fish fossils from that period, but it was shocking that compared to other fish, the physiological characteristics of this fish were so different!
It was about 2.7 meters long, its pectoral fin was more developed than other known fish at the time, and it not only grew bones that could support the "arm muscles", but also had flexible wrist joints, that is, it could not only swim in the water, but also climbed up to land through the "arms", in addition, its skull was also very unique, very similar to the skull of a quadruped. This means that this fish is likely to be the key point where the fish went out of the ocean and landed on land, belonging to the earliest ancestors of terrestrial creatures (naturally including humans).
Shubin named the fish TikTalik fish, and then published the relevant research in the journal Nature, which caused quite a stir in the academic community. Many people joke that if you can turn back the clock and go back to the land expedition that stopped the Tiktalik fish 380 million years ago, so that all fish will continue to live in the water, and the evolution from fish to quadrupeds will end, then there will be no human beings today, all the troubles of human society, and even the problems of the earth's ecological circle.
Of course, this is just a fantasy, but time cannot be turned back, but evolution can be—in a rock formation about 1.5 kilometers from the site of the Tiktalik fish fossil, Shubin and his colleagues also found fossil fragments of another fish. After years of hard work, in 2020, a research team at Penn State University finally restored the full picture of this fish, from the appearance, this fish is very similar to the Tik Talik fish, but its body size is a full circle smaller than the former, its body is covered with a layer of white scales, with sharp fangs in its mouth, apparently, this is a powerful predator who has lived in the water for a long time, and people have named it "Chikikitani Fish" according to the place name of the excavation site.
Similarly, the Chiquiktani has a nearly intact pectoral fin and well-developed humerus (the bone that supports the upper arm), radius and ulna (the bone that supports the lower arm), that is, it has begun to evolve limbs and prepare to land. However, when the Chiquiktani fish's evolutionary path came to this point, it suddenly turned its head - its humerus was very thin, shaped like a boomerang, and it looked weak and weak, and it was difficult to fully support its body. Based on this, scientists speculate that the Chikikiktani fish once tried to leave the ocean and climb up to land following the example of the TikTalik fish, but somehow it gave up this temptation halfway, fought a retreat, and returned to the water.
It can be seen that the evolution of organisms does not go all the way along a straight line, and there will often be many forks in the way of evolution, some continue to move forward, some may stop in place, and some may return to the same way.
