Snakes are seemingly simple in structure, a head attached to a long, unremarkable noodle. They do have some pretty cool features at the front end, with venomous fangs and the capability to stretch their mouths and swallow large prey whole, but their bodies are not just the simple tubes we once thought.
My new research, published in the Journal of Morphology, reveals their body structure to be surprisingly complex — far more than we once thought. In fact, it shows snakes have among the most complex spines in reptiles.
Let’s talk about vertebrae
Let’s first talk about vertebral columns. Within our own spines, we have three main regions.
First is the cervical region, or neck, which supports our heads and gives us mobility to look around. Next is the thoracic region, with ribbed vertebrae to protect our internal organs. Finally, we have the lumbar region in the lower back, whose main function is to support our upper bodies.
Within each region, the vertebrae have distinct shapes based on the functions they serve, and we can see this in a host of different animals.
When it comes to snakes, however, the story becomes a bit more complicated. Snake vertebrae similarly change shape throughout the column, but the boundaries between these regions aren’t as clear-cut.
This led to a lot of early research concluding that snakes just had one big, long body, with a uniform gradient of change throughout.
But this was not the consensus, and debates raged until a seminal paper in Nature came out in 2015.
It found that snakes do, in fact, have regions — four, in fact: the cervical, anterior thoracic, posterior thoracic, and lumbar regions.
However, a decade on, my findings change a few things.
Snakes have short necks
Colleagues and I took three Australian snake species: the eastern brown snake, copperhead, and tiger snake.
We measured the shape of every single body vertebra in 13 snake specimens. By quantifying each vertebra’s shape, we can study how it changes along the body.
What we found is not a uniform gradient of change, but rather some areas of rapid change and some areas without. This corroborates that snakes do, in fact, have regions within their bodies where there are sections of vertebrae that have a similar regional shape, then a rapid transition zone into the shape of another region.
By looking at this much detail, we found five regions within a snake’s body — not four. We also found that snake necks are shorter than once thought. While previous research thought of the neck as long, up to 15% of the body, we show it’s more likely to be around 5% of body length.
This means snake necks are around 7 to 12 vertebrae long, similar to their lizard cousins. This suggests that while snakes elongated other parts of their body, their necks retained a more ancestral form, remaining short throughout evolution.
Changes reflect ecology
We also found a previously undescribed region, which we are calling the middle thoracic region, as it’s nestled between the anterior and posterior thoracic regions.
This finding contributes to an emerging theory, where limbless animals have undergone shifts in their vertebral columns. Basically, if you don’t have any limbs, the only way for you to adapt to your environment is by changing your entire body.
Overall, we see how snakes retain ancestral regions within their vertebral columns despite limb loss and elongation. But they have also gone further, repatterning their vertebral columns to be even more complex than their limbed counterparts.
Ammresh, Ph.D. Candidate, School of Biological Sciences, Monash University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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