I’m not kidding you, you can really add legs to a snake!

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There are snakes in the pictures in this article. Friends who are afraid of snakes please read carefully.

If I were to use an idiom to describe the picture below, it would definitely be - adding legs to a snake.

Artistic reconstruction of a Najash snake｜Raúl O. Gómez

But this is not superfluous, snakes with long legs once really existed. In the long process of evolution, in order to survive, snakes gradually lost their limbs and even became "aliens" with loose skull joints.

Draw a snake and you can add legs

In 2003, paleontologists discovered the fossil of a prehistoric snake in Patagonia, Argentina. The snake was not very attractive, but it had a pair of fully developed hind limbs. The snake lived in the Late Cretaceous period about 90 million years ago and was named Najash rionegrina by paleontologists.

Heihe Shengyou Snake fossil, slide left to see the bone markings, fem is femur (femur)｜Hussam Zaher

The Heihe Shengyou Snake fossil fills in an important piece of the puzzle in the evolutionary history of snakes. A paper about this fossil was published in the journal Nature in 2006.

Previously, although people believed that snakes lost their limbs during evolution, they had not found evidence on land. Paleontologists once speculated that the ancestors of modern snakes may have lost their limbs in the water and had no feet when they came ashore; the giant marine reptile Mosasaur with limbs was therefore considered to be the ancestor of snakes.

But the Heihe Shengyou snake was found in terrestrial sediments and lived on land, which overturned the previous hypothesis and proved that the land ancestors of snakes could also grow legs. In addition, the Heihe Shengyou snake not only retained its hind limbs, but was also the first snake discovered to have a sacrum, a bone that supports the pelvis and hind limbs.

Artistic Restoration of the Black River Sacred Snake｜Jorge Gonzalez

The Heihe Shengyou snake is one of the closest snakes to the four-legged ancestors of snakes discovered so far. In 2015, an article in Science magazine claimed to have found the first snake with four legs in history; but subsequent studies believe that this "ancient four-legged snake" that lived 120 million years ago should be classified as a lizard rather than a snake.

Tetrapodophis amplectus, which lived 120 million years ago, was probably a lizard, not a snake | Jorge Gonzalez

"Autism" creates a slender figure

If modern snakes saw the scorpion snake, they would probably think that these legged ancestors were very strange. But in fact, the body shape of the scorpion snake is very similar to some existing vertebrates. For example, some species of skinks have only very short limbs; bipedal caecilians, amphibians such as giant eels and amphibians all have only short vestigial forelimbs.

Moreover, these animals have one thing in common: they live in caves. Their long and thin bodies are very suitable for digging under sand or mud, and their short remaining limbs can kick the mud out of the cave to prevent it from clogging the cave.

The five-toed bipedal caecilian lizard Bipes biporus retains a pair of tiny "hands" | marlin harms / Wikipedia

Chalcides chalcides skink, with cute little legs | Hjvannes / Wikimedia Commons

One of the most primitive groups of existing snakes, the blind snakes, also live in burrows in the soil and feed on insects and other small invertebrates in the soil.

Paleontologists believe that the ancestors of snakes in the Mesozoic era were also burrowing animals. At that time, in order to avoid the threat of dinosaurs, crocodiles and other ancient reptiles on the ground, some lizards were forced to burrow underground. In order to adapt to the life of digging and moving in the soil, their limbs, shoulder girdle, sternum and pelvis gradually degenerated and disappeared, and gradually evolved into the snakes we are familiar with today.

The Ultimate Evolution of Going Underground

Snakes' adaptive evolution to cave life is more than just losing limbs.

In order to accommodate the internal organs in the narrow body cavity, the left lung lobe of snakes shrinks and loses its function, and even disappears completely in more advanced species. At the same time, the right lung lobe is very developed, up to one-third of the snake's total length, and is responsible for breathing and storing air, allowing snakes to lurk underwater or in oxygen-deficient underground for a long time. In addition, the kidneys and gonads of snakes are not symmetrical like those of most vertebrates.

Diagram of snake internal organs, 4 is the atrophied left lung, 5 is the right lung｜Uwe Gille / Wikimedia Commons

The eyelids of snakes are also specialized into a piece of immobile transparent eye scales, covering the eyes, just like goggles to protect their eyes from being scratched by gravel and stones. So, in fact, snakes always keep their eyes open, just wearing a pair of "swimming goggles".

Now that snakes have lost their limbs, the way they move needs to change.

Slow-moving viper Bitis sp. | ojatro / youtube

Snakes have fewer cervical and caudal vertebrae, but their bodies are very long. The numerous ribs are not fused with the sternum, and can move independently under the pull of the costal skin muscles. At the same time, the snake's abdomen has a row of specialized enlarged ventral scales, and the skin is relatively loose. Under the pull of the ribs and costal skin muscles, it is like taking countless pairs of small feet to drag the body forward. Combined with the twisting of the body, snakes can crawl quickly and flexibly on the ground, and can even use the ventral scales to fix themselves and climb up smooth tree trunks or vertical rock walls.

Since the limbs are not needed for movement, the hind limbs and pelvis of existing snakes have almost completely disappeared. Only the python and anaconda families have the remains of hind limbs and pelvis called "residual feet". Male pythons and anacondas will use their residual feet to rub and scratch the skin of females when courting, "persuading" them to mate with them.

Remaining limbs of Simalia boeleni | Mokele / Wikipedia

Relax your mind to eat

The Patagonian Dinilysia patagonica, also found in South America, lived 5 million years later than the holy snake. Compared with its "predecessor", the Dinilysia patagonica not only has completely degenerated its limbs, but also has its skull joints become looser and more flexible.

This is a very important adaptive feature for snakes: due to the loss of limbs, snakes cannot tear their prey into pieces like monitors and crocodiles when eating, but must swallow them whole. A loose and flexible skull allows them to swallow prey that is much larger than their own body.

Thermal diagram of a snake eating a mouse｜Arno / Coen

The Megalosaurus family took the swallowing ability to a higher level. This type of snake appeared in the Cretaceous period and survived until the Cenozoic era. Some of its large and medium-sized species could even prey on the young of large dinosaurs and small dinosaurs.

Most existing snakes have independently movable quadrate bones, and their swallowing ability is even stronger than that of the Megalosaurus. Most common snakes can easily swallow prey that is three times the width of their skulls, and some snakes can even swallow food that is larger than their own body.

An intact red duiker (Cephalophus natalensis) was found in the stomach of the Gaboon Adder (Bitis gabonica) | Jonathan Kirk Warner / Conservation Biology of the Gaboon Adder (Bitis gabonica) in South Africa

Today, the strange appearance of snakes has left a deep imprint in the indigenous cultures of almost all over the world. They are either worshipped as gods or regarded as demons and avoided as much as possible. Looking back at the long history of evolution, the asteroid 66 million years ago wiped out non-avian dinosaurs, pterosaurs and most marine reptiles; the small mammals, lizards and frogs that survived the disaster quickly and proliferated in large numbers on the wasteland.

Snakes, which also survived the Cretaceous extinction, relied on their slender, flexible, limbless bodies to move flexibly in dense vegetation and narrow cave crevices. Their flexible large mouths that could "swallow the sky and the earth" allowed them to prey on small prey; coupled with their low metabolic rate, snakes grew rapidly and evolved into one of the most successful reptile groups on Earth today.

The World Health Organization logo, with a snake wrapped around the stick, is the staff of Asclepius, the god of medicine.

Author: Black-scaled cockscomb snake

Editor: pee pee shrimp, maimai

This article comes from the Species Calendar, welcome to forward

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