Ancient discovery: Adding legs to a snake?! Why did snakes lose their limbs?

Xinhua News Agency, Nanjing, January 27 , titled: Adding legs to a snake?! Why do snakes lose their limbs?

Xinhua News Agency reporter Wang Jueyin

Snakes are a type of animal that actually exists in nature. Throughout history, human ancestors had many encounters with snakes. Many ancient civilizations have legends related to snakes. In ancient my country, there is also the allusion of "adding legs to a snake". So, how did snakes originate and evolve? In the long evolution, are there any "star snakes" worth talking about? Why did they "lose" their limbs? Paleontologists and popular science experts will popularize the mysteries of snakes for you.

He Yiming, director of the exhibition department of Nanjing Paleontological Museum, said that snakes are generally referred to as snakes, belonging to the Lepidosauria order under the Reptiles class. Lepidosauria includes animals such as lizards and snakes that we are familiar with today. If we explore the origin and evolution, modern snakes and their ancestors can be classified as "Panserpents" and traced back together.

Simply put, "Pan-Snakes" are a group of lizards that look very much like snakes. It is now generally speculated that snakes evolved from lizards, and the two are very closely related. The earliest Pan-Snake lizard discovered by humans is the Ong's Dawn Snake, which lived in the Jurassic period 160 million years ago, and the earliest clear snake fossil is the Sanctuary Hasserius, which was found in the West Bank, dating from the Early Cretaceous period 112 million to 94 million years ago. The snakes discovered in ancient times mainly lived in oceans, swamps, forests and other environments, which are very similar to the living environment of modern snakes.

"In the evolutionary history of snakes, some 'star snakes' have attracted much attention due to their huge size and unique way of survival. The most famous giant snake is the Titanoboa." He Yiming introduced that its fossils were found near the Cerrejón coal mine in northern Colombia, South America, and it lived in the Paleocene Epoch about 60 million to 58 million years ago. The Titanoboa reached an astonishing size of 12.8 to 14.3 meters and weighed 730 to 1,135 kilograms. It was once considered to be the top predator that appeared after the extinction of non-avian dinosaurs.

Reconstruction of Titanoboa. (Drawn by Yang Dinghua)

Compared with their four-legged ancestors, lizards, snakes have lost their limbs. Why? The loss of snake limbs is a complex and long evolutionary process. The current mainstream view is that this change is to adapt to underground life, allowing snakes to dig holes underground to better hunt and escape natural enemies.

Shi Jingsong, a postdoctoral fellow at the Institute of Zoology, Chinese Academy of Sciences, said that the burrowing life of early snakes often required organisms to have more flexible bodies and stronger environmental adaptability in order to adapt to the narrow, complex and changeable spatial environment. This selection pressure may have prompted a series of adaptive changes in the body structure of snake ancestors, such as a more slender body, a more flexible spine, and a more developed structure of the inner ear related to hearing and balance. Secondly, the burrowing environment may have reduced the necessity of limbs in movement and hunting, thereby accelerating the process of limb degeneration. "In many early snake fossils, we can see the existence of short fore and hind limbs, and even in living pythons there are remnants of a hind leg."

The remains of the hind legs of a living python. (Photo by Shi Jingsong)

In general, as a key node in the evolution of vertebrates, the evolutionary history of snakes is of great significance to human understanding of the entire animal evolution. The successful evolution of snakes not only demonstrates the diversity and complexity of biological adaptive changes, but also allows the population to continue to prosper. Now, the distribution range of snakes spans all continents in the world except Antarctica, and they are undoubtedly one of the most successful terrestrial vertebrate groups in contemporary times.