Snakes and Their Deceptive "Tails": An Evolutionary Exploration

Snakes don’t have a tail in the traditional sense—what we think of as a snake’s tail is actually part of its spine. Snakes have a single, long backbone that spans from their skull to the very end of their body. While it tends to be thinner and more flexible toward the end, a snake’s tail is a crucial part of its skeletal makeup.

In this article, we’ll take a deep dive into studies from the fields of herpetology, evolutionary biology, and animal morphology to explain the evolutionary adaptations that have led to the snake’s elongated body plan, the many purposes their tails fulfill, and the specialized skeletal components that make their movement and agility possible. This investigation will help you understand the complex ways snakes have adapted to their surroundings.

Anatomy of a Snake's 'Tail'

The anatomy of a snake's posterior region, which is often called the "tail," is an interesting example of evolutionary adaptation. This part of the body is not a separate appendage but an extension of the snake's vertebral column, which is made up of a series of vertebrae that can differ greatly in number from one species to another.

As explained by Reptiles Magazine, the last 25% of a snake's body contains organs such as the ileocecal junction, the cecum (in some species), the kidneys, and the cloaca. The number of vertebrae in the tail can vary from about 10 in some species to more than 200 in others, with the Australian python having up to 205 caudal vertebrae, according to Britannica.

Although most snakes don't have external limbs, the remnants of the pelvic girdle and femur are present in a number of families, including boas and pythons. These vestigial structures are thought to be a holdover from their limbed ancestors and provide a window into the evolutionary past of these reptiles.

Some snake families have evolved special skeletal adaptations in their tails. For example, rattlesnakes have highly modified vertebrae at the end of their tails that make up the "shaker" that creates the sound of the hollow rattle segments, according to Britannica.

The outside of the tail is covered in the same keratinous scales that protect the rest of the snake's body. However, some species have developed specialized sensory organs or muscular adaptations in this part of the body. For example, as noted by LafeberVet, sea snakes have flattened tails that help them swim, and burrowing snakes often have spiny tails that help them anchor themselves in the soil.

Locomotion: How Snakes Move Without Legs

Snakes have adapted to move in a variety of ways without the use of limbs, and their anatomy and locomotion strategies have adapted to make this possible. According to research on snake locomotion, they use at least five different modes of terrestrial locomotion.

The most well-known is lateral undulation, in which waves of lateral bending travel posteriorly along the body, enabling the snake to push off of objects and move forward. The research notes that this mode requires objects to push off of, although some snakes can move in this way on a flat surface due to the directionally dependent frictional properties of their scales.

Many snakes use sidewinding to move on smooth or slippery surfaces, in which every point on the body is in static friction with the surface, and the body is lifted and rolled diagonally across the surface, as explained in the research. The 'tail' is particularly important in this mode, as it provides the snake with the necessary weight distribution and flexibility to move in this way.

When snakes need to move in a confined space, they use concertina locomotion, in which they move their body in a series of bends and then straighten out to move forward, using static friction against the surface to move, as described in the Journal of Experimental Biology. The 'tail' region is important in this mode because it provides the snake with the stability and points of contact it needs to move.

Rectilinear locomotion is often used by large, heavy-bodied snakes, and in this mode, the snake uses its ventral scales to grip the surface and pull its body forward in a straight line, with the 'tail' helping to distribute the snake's weight, according to the PMC research.

The 'tail' has also evolved in some snake species, such as arboreal or aquatic species, to help them move in their preferred modes of locomotion, as noted in the Britannica entry on snake anatomy.

Sensory Capabilities: The Nervous System and Senses in Snake Tails

The snake's 'tail' region is densely innervated by an intricate network of sensory nerves that originate from the spinal cord. According to the WikiVet English article on the snake neurological system, the spinal cord extends the entire length of the vertebral column and gives rise to sensory and motor nerve roots at each vertebral segment. This enables the 'tail' to both receive sensory information and send motor signals, enabling its many functions.

In some snake species, the 'tail' has evolved specialized sensory organs. For example, pit vipers such as the western diamondback rattlesnake have a pair of heat-sensing pits on their face that are connected to the optic tectum in the brain, according to Snakes on the Brain. These infrared receptors can detect changes in temperature as small as 0.001°C, enabling the snakes to strike accurately at warm-blooded prey even in total darkness.

The 'tail' may also be involved in environmental sensing, helping the snake move through tight spaces, and detecting predators or prey. For example, studies have found that the pit organs in the tails of rattlesnakes are extremely sensitive to tiny changes in temperature, which could help the snakes detect prey and avoid predators. Meanwhile, the fact that blindfolded rattlesnakes can still strike accurately at moving objects suggests the 'tail' may have specialized mechanoreceptors that detect vibrations and movement.

Tail Diversity and Function in Snakes

The snake world is full of an amazing array of tail types and adaptations, all of which have evolved to help snakes survive in their specific habitats and ecological niches. As a study in Behavioral Ecology notes, snake color patterns, including those on the tail, are closely linked to a number of factors, including hunting style, speed of escape, and defensive behaviors.

For instance, as the Britannica explains, arboreal snakes often have prehensile tails that help them climb and hold on to branches, while aquatic snakes may have tails that are flattened and paddle-shaped to help them swim. Meanwhile, the Functional Ecology study found that arboreal snakes have relatively longer tails, which may help them reduce the cardiovascular costs of climbing.

Tail length and shape can also be influenced by reproductive considerations. As a study in Scientific Reports suggests, in some snake species, longer tails in males may be a sign of better individual quality, which could help them win more mating opportunities. However, the same study also found that longer tails in males may come with costs, including reduced reproductive success in females.

Throughout the snake evolutionary tree, the variety of tail shapes and their functions is a testament to the incredible adaptability that has helped snakes conquer a wide range of habitats.

The Evolution of the Rattlesnake Rattle

The rattle of the rattlesnake is a prime example of evolutionary adaptation. As outlined in a study published in BMC Ecology and Evolution, the rattle is a complex aposematic sound-producing structure composed of keratinous, multilobed, interlocking segments. The site of actual rattle segment formation is the end-body, which includes the style - a combination of fused and modified caudal vertebrae that provide a point of insertion for the powerful tailshaker muscles.

The study proposes that the rattle evolved from ancestral tail vibration behaviors in rattlesnake ancestors. As described in Science News, ancestral snakes that made noise with their tails may have been more successful at scaring off predators, leading to the development of traits like keratin calluses that eventually became the rattle.

This adaptation has allowed rattlesnakes to develop an effective warning signal that helps them avoid predation through the loud, distinctive rattle sound. Yet, the evolution of the rattle may have also had costs, like increased energy demands or decreased locomotor performance, as the BMC Ecology and Evolution study notes.

The study also shows that the rattle has a wide range of morphologies across rattlesnake species, which may be linked to specific ecological or behavioral differences. This indicates that the form and function of the rattle has continued to evolve to meet the needs of different rattlesnake lineages.

Conclusion: The Many Roles of the Snake Tail

The snake's "tail" is a key part of the snake's body that has enabled the reptiles to thrive in a wide variety of habitats and ecological niches. From prehensile tails that help arboreal snakes to paddle-like tails that help aquatic snakes, the "tail" has been critical to the snake's success.

Understanding the snake's "tail" and its many adaptations and roles provides important insights into the snake's evolution and the many ways it has adapted to its environment. Although often overlooked, the snake's "tail" is a critical part of the snake's body that makes its many abilities and behaviors possible.