When I was diving deep into research for VENOMOUS SECRETS, I studied a lot of lamia images on the internet. Most were women from the waist up, snakes from the waist down. And because my books delve into biology, both real and not-quite-so-real, you know I started wondering about possible underlying anatomy.
And down the rabbit hole I fell.
After considering what passes for mermaid skeletal anatomy on the internet – all in possession of pelvic bones – I decided to stick with snake anatomy for the lower half of my lamia. Which sent me deeper into the rabbit warren of snake skeletal anatomy.
So many ribs. For comparison’s sake, we possess twelve pairs of ribs. Snakes? They can have upwards of 300 pairs!
How???
Yes, I wondered too. Being the biologist I am, I delved deeper. Into the very genetics of snake skeletal development.
Snakes, like us, are vertebrates. In other words, they have a spinal column. Before we consider serpents, let’s review vertebral anatomy. Each type of vertebra has a distinct morphological shape that is conserved across all vertebrates – which is a way to say they’re largely the same, with some adjustments by species.
Cervical vertebrae are those of our neck, thoracic vertebrae are those that support the ribs, lumbar vertebrae are large and weight bearing, sacral vertebrae (fused to make up the pelvis which in turn connects to the legs) and caudal vertebrae (aka the tail – coccyx in humans).
So how do we get 200+ thoracic vertebrae in snakes?
To answer that, we have to back up to embryological development.
All along the developing neural tube, repeating blocks of tissue form called somites. These are the first step in setting up the pattern for the vertebral skeleton. From head to tail, more and more Hox genes are expressed, instructing the somite as to which kind of vertebrae it’s supposed to become. Change the expression of a single Hox gene (or shift it closer or further from the head) and you change the identity of the vertebrae created.
Using genetic tricks, snakes have reduced the number of cervical and lumbar vertebrae (see chart above).
Who knew? Snakes have necks, albeit really short ones. Trivia we needed to know, right? 😉
But 200 thoracic vertebrae!!!
Right. To get so many rib-bearing vertebrae, you need a whole lot more somites. Snakes have developed this really cool trick where they run the developmental molecular clock faster, 4 times faster, creating far, far more somites during embryological development than for us humans and mice. And then they turn more of them into thoracic vertebrae.
But what about arms and legs?
That’s the other part of making a snake skeleton, right? Not making arms and legs.*
Turns out that snakes still have the gene for making arms and legs, a gene called sonic hedgehog (yes, named after the game) but… it never gets used because the regulatory DNA necessary to turn on the gene’s expression has been deleted.
Unless you’re a cobra or a viper. Not quite all of their sonic hedgehog regulatory DNA was deleted, letting them start, but not finish making legs. Some can even have small skeletal remnants hidden deep inside their body (a tiny rudiment of the femur).
So that’s how we make a snake skeleton. Speed things up so that we have more segments to work with then turn more of them into thoracic vertebrae. At the same time, eliminate arms and legs by deleting the DNA necessary to turn on a critical gene involved in building limbs.
But when it comes to the lamia in VENOMOUS SECRETS, we’re left to wonder about their strange biology and what, exactly, is going on…
*yes, tetrapods, so technically all legs
Read More:
Hox Genes and Regional Patterning of the Vertebrate Body Plan
From Lizard to Snake; Behind the Evolution of an Extreme Body Plan
How Snakes Evolved to Lose Their Legs
About Anne
Though USA TODAY bestselling author Anne Renwick holds a Ph.D. in biology and greatly enjoyed tormenting the overburdened undergraduates who were her students, fiction has always been her first love. Today, she writes steampunk romance, placing a new kind of biotech in the hands of mad scientists, proper young ladies and determined villains.
Anne brings an unusual perspective to steampunk. A number of years spent locked inside the bowels of a biological research facility left her permanently altered. In her steampunk world, the Victorian fascination with all things anatomical led to a number of alarming biotechnological advances. Ones that the enemies of Britain would dearly love to possess.
To chat with Anne, stop by on Facebook or join the Department of Cryptobiology Facebook group. You can also join her newsletter list to have cover reveals, sneak peaks, sales and giveaways delivered straight to your inbox.
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