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Are Snakes Tetrapods?

Although snakes have no visible limbs, they are still considered tetrapods because they are descended from four-legged lizards and still have vestigial appendages inside their bodies.

A coiled snake
Snakes have no visible limbs, but they have vestigial feet that enables them to be classified as tetrapods

Snakes do not have legs, but they used to. Pythons have appendages or vestigial appendages inside their bodies. Until today, they have hind leg bones, which are a testament to their evolutionary development.

What is a Tetrapod?

A tetrapod is an animal that has four limbs. In modern classification, it includes both extant and extinct species.

Tetrapods include amphibians, mammals, and even reptiles.  Any animal that has four feet is a tetrapod. However, it can be confusing because snakes and whales have no feet, yet they are part of the tetrapod group.

All in all, an organism that descended from a common ancestor that had four limbs is a tetrapod. For example, some birds are tetrapods even if they do not walk on four limbs.

In evolution, the earliest tetrapods were mammal-like reptiles. They had four feet. They lived before the time of the dinosaur. In those pre-historic times, tetrapods ranged in size. There were those that were as small as a mouse, and some were as big as cows.

Today, tetrapods comprise birds, mammals, reptiles, and amphibians. The fish, however, is not a tetrapod, even if it is a vertebrate.

Are Snakes True Tetrapods?

Snakes are true tetrapods because they evolved from a common ancestor with four limbs. In scientific parlance, snakes are also called squamates. These are limbless reptiles that have vestigial limbs. 

Snakes are still part of the tetrapod group because they descended from ancestors that have four limbs. If one would observe closely, many reptiles lay eggs on land, not in the water.

For example, crocodiles spend much of their time in the water, but they lay eggs on land. 

What this means is that they descended from an ancestor that had the ability to walk. Specifically, this ancestor is the Megachirella wachtleri. It is an extinct genus of a stem-squamate, and it lived about 240 million years ago.

What Did Snakes Evolve From?

Snakes evolved from lizards. Studies indicate that the slender and limbless bodies of snakes. The consensus is that the snakes originated about 128 million years ago. 

Not much is known about the evolutionary history of snakes. As such, there is a debate as to whether they evolved on land or in the ocean. 

To shed some light on this, a team of scientists studied snake fossils and living specimens. They analyzed various genes and fossils. In total, they studied 73 species, not only of snakes, but also that of lizards.

The team found out that the first snakes had vestigial limbs. They had hind limbs, and they lived in a warm ecosystem. They lived in wet forests. The study also resulted in a theory that they were nocturnal creatures. 

The trait of being nocturnal disappeared as the world’s climate changed. Nighttime temperatures decreased. The trait appeared again 50 million years later. 

By this time, the Colubroidea family has already evolved. Colubrid snakes are non-venomous ones that make up 85% of modern snakes today.

Lizard on a branch
You can see the resemblance with snakes in many modern-day lizards

Why Did Snakes Lose Their Limbs?

Snakes evolved from lizards and lost their limbs over time. The absence of limbs makes it easier for snakes to swim. It is also useful for burrowing. 

Read More: Can Snakes Swim Underwater?

Snakes also lost what is called the Sonic hedgehog gene, or the SHH. It is the gene responsible for developing legs. When snakes evolved, they lost this gene.

One point of contention about evolution is that losing limbs has no evolutionary advantage.

In 2016, there was a study proving that there was a change in the reptile genome of the snake. This change happened back when it was still part of the lizard family. These changes are what eventually separated them from the physical traits of the lizards. 

The genetic mutations caused the lizards to do away with their limbs or appendages. The final result is the modern snake, which transitioned to many species today. However, there are still remnants of these legs in their hips.

Did Snakes Evolve Venom Before Losing their Limbs?

Before the snake branched away from the lizard family, some lizards already had venom. For example, the Komodo dragon and the Gila monster already had venom.

According to Dr. Bryan Fry, an Associate Professor from the University of Queensland in Australia, venom is all about prey capture. The venom evolved before the snake did.

The thing is that different animals have different venom content. As a result, there are differences in the results of the hunt. It is the evolutionary differences in the venom. 

He also said that the differences in the prey in the environment have something to do with how venom evolved. Different preys forced animals to evolve the venom.

While venom has existed before snakes, it is the snakes that took venom to another level. There are many types of classifications of venoms, but there are three major types that snakes possess. 

These three are cytotoxic, neurotoxic, and hemotoxic. Although not all snakes are venomous, most snakes possess a mixture of the three. Snakes have different potency levels for these types of venom.

Read More: Are Baby Snakes Dangerous?

A cytotoxic venom dissolves tissue and muscle. It is like the venom of a spider. As the tissues dissolve, it will lead to hemorrhage and death. 

Haemotoxins are a type of venom that goes to the blood. They rupture the blood cells, resulting in internal bleeding. because of this, the blood clots and blocks the vessels and arteries. The final result is stroke and death. 

Lastly, the neurotoxin blocks the signal from the nerves. These signals do not reach the muscle. Because of this, the person will go through paralysis. Eventually, the person will suffocate and die.

Summary: Are Snakes Tetrapods?

Snakes are tetrapods even though they do not have visible legs or limbs. They are part of this organism grouping because they descended from an ancestor that had four limbs.

Snakes evolved from lizards, and they became snakes 128 million years ago. Some snakes today, like boas and pythons, still have remnants of vestigial limbs.

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