The ‘Ssseriously’ Strange Anatomy of Snakes
By: Michaela S. Bouffard
Let's imagine you are a snake. What are you feeling as you slither through the long grass that surrounds you? With no limbs, infrared sensing, and 300 vertebrae, life is a bit different. Snakes have evolved to be some of the most unique and fascinating specimens in the animal kingdom, but what makes their anatomy so spectacular?
Snakes can do what?!
Snakes can see heat. Yes, you read that right. More specifically, some snakes can detect infrared heat using facial pits (little holes on their face) which act as an extension of their visual system. These infrared and visual messages work together to tell snakes where they can find prey and thermoregulatory opportunities (Krochmal and Bakken, 2003). Inconveniently, they can’t focus this extra sense as well as we might expect (Clark et al. 2022), meaning they need to rely on other means to gain accuracy. This is where the vomeronasal organ (also known as the Jacobsons organ) comes in. The reason snakes spend so much of their day with their tongue poking out of their mouth is because they are using it to smell their surroundings. Their tongues can pick up airbourne chemicals that are processed by the very sensitive vomeronasal organ, which allows them to find prey, predators, and mates (Miller and Gutzke, 1999).
Now that we know snakes have super-sniffing, heat detecting senses to find their prey, how do they eat? They don’t have arms, yet they can consume massive prey in comparison to their own body size. Venom is a key player in the ability of snakes to obtain food. There are three main types of venomous snakes: opithoglyphs, which are rear-fanged, and then the proteroglyphs and solenoglyphs are front-fanged (with immobile and mobile fangs, respectively) (Haji, 2000). The venom excreted by these fangs can have varying effects on their prey, including haemotoxic, neurotoxic, and cytotoxic properties (Oliveira et al. 2022).
Once the snake has immobilized its prey, it uses its super flexible skull to maneuver its dinner into its mouth. Snakes have highly kinetic skulls, allowing for extreme mobility and in directions we as humans cannot move in. Humans have one part of our skulls that can move, which is the temporomandibular joint (TMJ). Snakes on the other hand, can move the majority of the components of their skulls, which allows for hands-free meal times. In addition, snakes also have independently moving sides to their upper (maxilla) and lower (mandible) jaws that are connected by ligaments, so they can crawl their mouths over their prey instead of relying on hands to feed themselves (Deolindo et al. 2021).
Snakes also have to arrange their organs differently in their tube-like body. For this reason, their organs are elongated and staggered, allowing for blood supply throughout the entire individual’s svelte body (Bellairs and Underwood, 1951). This leads to another space saving feature: many species of snakes have evolved to ditch one of their lungs. There is simply no space for two, yet the diffusion capacity of snakes is similar to turtles, who have retained both functioning lungs (Stinner, 1982).
Superspeed evolution
Snakes belong to an order of species called squamates (lizards, snakes, and amphisbaenians). Although scientists are not sure why, snakes began to anatomically differentiate themselves from their lizard counterparts 128 million years ago (Rieppel, 1988), giving rise to protosnakes, which are essentially long lizards with stubby, non-functional legs. Although squamates have adapted to life without legs over 25 separate times throughout evolutionary history (Morinaga and Bergmann, 2020), it was the snakes that truly thrived. They did so well with their new body form that the rate of evolution increased threefold, leading to macroevolutionary singularity (a boom of new adaptations) (Brandley et al. 2008). From here, they began to rule with flexible skulls, venom, the ability to detect airborne chemicals and heat, and the power to constrict their prey. We are not sure whether this unique combination of features evolved to suit their burrowing or locomotor habits (Shine, 1986), but whether you love them or hate them, these noodle shaped reptiles are excelling at their craft.
Literature Cited
Bellairs, A. D. A., & Underwood, G. (1951). The origin of snakes. Biological Reviews, 26(2), 193-237.
Brandley, M. C., Huelsenbeck, J. P., & Wiens, J. J. (2008). Rates and patterns in the evolution of snake-like body form in squamate reptiles: evidence for repeated re-evolution of lost digits and long-term persistence of intermediate body forms. Evolution, 62(8), 2042-2064.
Clark, R. W., Bakken, G. S., Reed, E. J., & Soni, A. (2022). Pit viper thermography: the pit organ used by crotaline snakes to detect thermal contrast has poor spatial resolution. Journal of Experimental Biology, 225(24), jeb244478.
Deolindo, V., Koch, C., Joshi, M., & Martins, A. (2021). To move or not to move? Skull and lower jaw morphology of the blindsnake Afrotyphlops punctatus (Leach, 1819)(Serpentes, Typhlopoidea, Typhlopidae) with comments on its previously advocated cranial kinesis. The Anatomical Record, 304(10), 2279-2291.
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Miller, L. R., & Gutzke, W. H. (1999). The role of the vomeronasal organ of crotalines (Reptilia: Serpentes: Viperidae) in predator detection. Animal Behaviour, 58(1), 53-57.
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Oliveira, A. L., Viegas, M. F., da Silva, S. L., Soares, A. M., Ramos, M. J., & Fernandes, P. A. (2022). The chemistry of snake venom and its medicinal potential. Nature Reviews Chemistry, 6(7), 451-469.
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Shine, R. (1986). Evolutionary advantages of limblessness: evidence from the pygopodid lizards. Copeia, 1986(2), 525-529.
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