Snakes aren’t simple tubes. Their bodies have five regions – including a short neck

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An eastern brown snake (Pseudonaja textilis).<br>Ammresh, CC BY-NC

https://theconversation.com/snakes-arent-simple-tubes-their-bodies-have-five-regions-including-a-short-neck-288904

https://theconversation.com/snakes-arent-simple-tubes-their-bodies-have-five-regions-including-a-short-neck-288904

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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 today 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 region, 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<br>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 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.

Snakes have five distinct regions in their bodies: the cervical (or neck), anterior thoracic, middle thoracic, posterior thoracic and lumbar.<br>Ammresh, CC BY-NC

Changes reflect ecology

We also found a previously undescribed region, which we are calling the middle thoracic region, as it’s nestled in between the anterior and posterior and 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.

Evolution

Snakes

Vertebrates

New research, Australia New Zealand

Ammresh, Monash University

Author

Ammresh

PhD Candidate, School of Biological Sciences, Monash University

Disclosure statement

Ammresh does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

Partners

Monash University provides funding as a founding partner of The Conversation AU.

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DOI

https://doi.org/10.64628/AA.xcq5xhes7

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