If there’s one animal on the plant that looks like it has no bones, that has to be the snake.
These agile and sleek crawlers possess the graciousness of a reptilian ballerina and are capable of moving at impressive speeds on land, despite lacking any limbs for locomotion.
Despite the appearance, though, snakes do have bones and a lot of them. Around 300-400 of them, to be more precise, can seem paradoxical.
How is an animal that possesses 400 bones so agile, gracious, and precise in its movements, as if it has no bones at all?
Let’s talk about it!
Anatomy of a Snake’s Skeletal System
The snake’s skeletal system consists of three major sections:
1. The Head
The snake’s head-to-body ratio can vary depending on the snake’s size and species. Pythons, for instance, have wide heads and rectangle-shaped jaws, allowing them to swallow extremely large animals.
Venomous snakes tend to have smaller heads. But all snakes, no matter their head size or shape, share the same unique feature: extreme jaw mobility.
In short, the snake’s mandible isn’t attached bone-on-bone to the upper jaw. Instead, the connections between the two jaws are made of flexible ligaments. This allows the mandible to move independently and exhibit a wider range of motion than in mammals, for instance.
This evolutionary feature allows snakes to hunt, kill, and consume larger prey, which can nourish them for longer. This is especially useful, given the snakes’ low metabolic rates; so, they eat rare, but when they do, they eat a lot in one go.
2. The Spine
You can consider the spine to be the snake’s main movement system. The spine consists of hundreds of small vertebrae connected by flexible joints, allowing the snake to move in ways inaccessible to other animals.
It’s interesting to note that the tail vertebrae are both smaller and more flexible compared to the ones in the midsection.
One of the spine’s main roles is to aid in locomotion, but some snake species can use it to increase their survivability as well. These snakes can actually dislocate their vertebrae to escape predators and flee. It’s a harmless feature, as the vertebrae fall into their place as soon as the snake contracts its muscles to slip them back.
The boa constrictor, garter snake, Brahminy blind snake, and rubber boa are known to possess this ability.
3. The Rib Cage
This section is also different than that of most other animals. Snakes don’t possess individual ribs but a rib cage, where all ribs are fused together.
This allows them to move in tandem, depending on the snake’s intentions and can expand to allow the snake to swallow large prey.
The rib structure is called a costal arch, which is very flexible due to the ligaments holding it together.
The structure has basically 3 fundamental roles:
- Protect the vital organs
- Expand the body to allow the snake to swallow larger prey
- Aid in locomotion
The latter point is particularly important because snakes actually use their costal arch when moving. The entire skeletal system aids in locomotion, allowing some snakes to reach speeds of up to 20 mph or more, depending on the species.
The snake’s skeletal system also works to the snake’s advantage when hunting or defending itself. Constrictor snakes rely on their muscles and vertebrae flexibility to squeeze the life out of their prey.
Large Burmese pythons, boa constrictors, and anacondas can even kill humans.
In terms of defense, the rattlesnake and the cobra are 2 of the most important representatives. They both use body positioning to enter a defensive state. Rattlesnakes curl into a defensive ball with their head on top of the ball and the tail out, ringing warning to potential intruders.
The body positioning allows the rattlesnake to explode like a spring and deliver its envenomed bite at lightning speed if necessary.
Cobras also use their body for defensive purposes, but in a different manner. Instead of curling up, they actually raise their bodies and inflate their hood (which is ribs expanding the body, by the way).
This is a threatening stance meant to make the snake appear larger and more intimidating. If that fails, the cobra will move to plan B, which is delivering its lethal venom.
Cartilage Structure in Snakes
The snake’s cartilage structure allows the reptile to move seamlessly through even the most rugged and demanding terrain.
The same cartilage structure is responsible for the snake’s ability to expand its spine and body to accommodate larger prey or detach the mandible from the upper jaw for the same purpose.
Cartilages are actually more resilient than the bones themselves, which makes sense, given the stress they’re subjected to.
Evolution of Snake Skeletal System
The snake’s skeletal system has evolved dramatically over time. Studies suggest an evolutionary time window of millions of years, starting with the snake’s earliest common ancestor and reaching today’s species.
Overall, several changes have taken place in the snake’s skeletal structure over time, including:
- The head – The snake’s head bones become more elongated with time, allowing for flatter heads with larger mouths. This allowed the snake to retain a lower profile, so it could squeeze through tighter spaces and make it harder to detect. The jaw also developed linking ligaments and cartilages that allow it to separate from the upper jaw. The mandible can also separate in the middle so that the 2 halves can move independently and force the prey down the throat with the help of the teeth.
- The spine – The snake’s common ancestor was thought to have been a lizard-like reptile that spends its time in burrows. This lizard had short and stocky vertebrae, which were coherent with the animal’s environmental requirements and lifestyle. The reptile soon evolved longer vertebrae that fused together in a compact mass via cartilages and ligaments. This modification allowed the animal to move more graciously through its environment and eventually led to the first iterations of the modern snake.
- Vestigial limbs – It’s clear that the snake’s common ancestor had limbs similar to those of contemporary lizards. It’s unclear, though, when the limbs began receding, but it’s relatively easy to determine why. This evolutionary adaptation is most likely the result of the animal adapting to its environment. The various changes in the snake’s natural habitat favored species with smaller limbs or no limbs at all. That’s because the lack of limbs actually benefits the snake, as it allows it to traverse rugged terrain easier and remain undetected by prey or predators while doing so.
- The rib cage – The rib cage also had to adapt to the snake’s ever-evolving anatomical structure. The snake’s rib system adapted to the snake’s increasing body length and eventually became a compact system with fused ribs. It eventually became what we know now as the costal arch, and we’ve already discussed how the costal arch enhances the snake’s anatomy and functioning.
Even more importantly, all snakes are still evolving, although you may not be able to observe the changes in real-time.
Not always, anyway. It’s important to note that evolution is a continuous process. It’s not like snakes evolved from legged animals to legless creatures in the span of one generation.
There has never been a legged snake giving birth to a legless one at any point in history.
Instead, it took millions of years for snakes to reach the stage they’re at today. This only makes you wonder where they’ll be hundreds, thousands, or even millions of years from now.
Impact on Movement of Bones
Snakes are unique in the animal kingdom in how they use locomotion. Snakes used the so-called serpentine locomotion method, which involves muscles using the vertebrae to propel the reptile forward.
The ribs also play a major role in this system, as the belly muscles form waves that allow the snake to move forward.
Interestingly enough, snakes can also use their belly scales to grip various surfaces, which allows them to climb rough areas and objects.
This shows that snakes are far more versatile in terms of locomotion than what an untrained eye might conclude.
Impact on Eating Habits of Bones
The jaw is the most impactful in this sense. Snakes have detachable jaws that are almost fully separated from the upper jaw. The only thing holding them together is a pair of strong and flexible ligaments.
The jaw also consists of malleable bones that separate in the middle. This means that the snake’s jaw actually consists of 2 bones fused together.
This bone system allows the animal to ingest large prey, larger than one might expect. But what happens once the prey is past the mouth?
That’s when the other systems kick in. Snakes possess an inflatable and flexible esophagus that can accommodate large foods passing through.
Going even lower down the intestinal tract, the snake’s ribs and muscles can expand to allow the prey to slide down seamlessly.
You can notice the result with the naked eye, as you can distinguish the snake’s inflated belly soon after it’s done eating.
You can even distinguish the prey’s anatomical features through the snake’s skin; that’s how flexible and versatile the snake’s digestive system is.
Diseases Affecting Snake Bones
Unfortunately, snakes can experience a variety of bone disorders, such as:
- Metabolic Bone Disease (MBD) – MBD rightfully occupies the first position because it’s the most common and impactful bone disorder that plagues reptiles in particular. This condition is, basically, the severe form of calcium and vitamin D3 deficiency, which reptiles are known for. MBD has no known cure, and it is deadly in its more severe forms. You can prevent the issue by providing the snake with a well-rounded diet and proper calcium and D3 supplementation, according to your vet’s recommendations. A good UVB light source also helps in this sense, as UVB lighting aids in vitamin D3 production.
- Scoliosis – This condition can be self-standing or occur as a complication of other health issues, especially MBD. Some of the most common triggers include injury, poor nutrition, and even genetic predisposition, the latter of which is the most prevalent. You can identify scoliosis via symptoms like a deformed spine, difficulty moving, difficulty breathing, abnormal head shape, visible stress, etc.
- Osteomyelitis – This is actually a bacterial infection that affects bones. The most common triggers are poor environmental husbandry, causing symptoms like swelling, fever, visible distress, etc.
- Osteodystrophy – This illness is most notably the result of severe nutritional deficiencies, especially phosphorus, vitamin D3, and calcium. The main symptoms include visible skeletal deformities, weakness, difficulty moving, lethargy, etc.
Snakes can also experience fractures, which are often the result of mechanical injuries. These are unlikely to occur in captivity but can happen due to poor handling or the snake attempting to escape its enclosure.
Fortunately, fractures are far milder and more innocuous than the diseases we’ve already mentioned.
Snakes are amazing and unique animals with a variety of astounding and species-specific characteristics.
Their skeletal system and its evolution over time are proof of Mother Nature’s incredible natural engineering and life’s adaptability and malleability.