Convergent Evolution in Snakes and Lizards

Convergent evolution in Snakes and Lizards is a phenomenon that gives real life evidence of how evolution works. There are a few examples that have been widely discussed, but so many more that are overlooked. Let’s focus on a few of these.

What is convergent evolution?

Convergent evolution is the development of similar traits in unrelated species that share a similar habitat or niche. Called homoplasies, or homoplastic traits, these similarities can involve appendages, appearance or even physiology.

Traits in general are adaptations that allow a species to enhance its chances of survival in its niche. Examples include colour, size, tooth shape, wings, fins, intelligence and pattern. When two animals end up filing a similar niche, they inevitably evolve homoplastic traits. This is true no matter how far apart they are geographically or phylogenetically. 

For example, one instance of a homoplastic trait is the pincer-like paws of a Koala and feet of a Chameleon. Both species are arboreal and (mostly) slowly moving, so they have evolved to have sturdy, gripping appendages. You can read more about this in my Herping Portugal post.

In the Squamata, which is the order containing all living snakes, lizards, and amphisbaenians, we’re spoilt for choice when it comes to examples of convergent evolution. This is because these groups are the most specious of the living reptiles and have filled similar niches repeatedly around the globe.

Everyone is familiar with the convergence between the Emerald Tree Boa (Corallus caninus) and the Green Treen Python (Morelia viridis), but as your about to see, there are some other, equally fascinating cases.

The Green Anaconda (Eunectes murinus) and the Leopard Keelback (Helicops leopardinus)

Green Anaconda from Sam Fisher

Sam Fisher holds a young Anaconda. Sam is a breeder who prides himself on producing healthy snakes. You can see more at www.fisherreptiles.com

The green anaconda is of course infamous for being the world’s heaviest snake and its second longest. The only ophidian that has reached a greater recorded length is the Reticulated python. Though impressive, the retic’ tends to stay a little slimmer in the wild. In captivity, they often get larger than anacondas, but people are only just starting to realise this.  

For this article though, we’re not interested in the aquatic gigantism that’s led to the anaconda’s huge size. We’re interested in the adaptations it has evolved to its water-loving way of life. Oh, and the fact that it has a little copycat: The Leopard Keelback (Helicops leopardinus).

Convergent Evolution in Snakes and Lizards

This photo of a Leopard Keelback snake was kindly provided by the Collett Trust for Endangered Species. The trust runs a wildlife reserve in North-east Argentina which provides a haven for grassland and wetland species – including this little snake. 

Like the Anaconda, the Leopard Keelback lives in the murky waters of tropical South America. Notwithstanding, it is very distantly related, being a colubrid, rather than a boa.

The shared aquatic lifestyle of these two species has led to them evolving a remarkable set of homoplasies.

Two very different species, but who both want to stay hidden when in the water

First, their overall colour and pattern is the same: dark spots on an olive background. When seen by predators or prey from above, this helps them blend into muddy water.

When in the water, both species need to breath air without being detected, which brings us to their second convergence.  They have eyes and nostrils positioned on the top of their heads and near to the end of the rostrum (snout). This head morphology allows an aquatic to animal to surface but keep most of its body hidden below the surface. 

To put this in perspective, it means an 18ft (5.4m) Anaconda can take a breath while only exposing an area of its head that is as large as the palm of my hand. This is ideal for stalking prey such as birds and capybara.

For the Keelback, which is much smaller, it means it can breathe without attracting the attention of predators. 

The Common Slug Eater (Duberria lutrix) and the Slow Worm (Anguis fragilis)

The Common Slug Eater is a small, southern African snake that has a predilection for terrestrial gastropods. I could tell you more, but Robert Wedderburn already does a great job in this video!

The Slow Worm, seen below, is a legless Anguid lizard that is a common resident in gardens across Europe. Apart from an obvious convergence with snakes in the matter of legless-ness, the females and young of the species have a two-toned colouration and dorsal stripe that are strikingly similar to those of the Slug Eater.

The Slow Worm (Anguis fragilis)

This is a case where two species share an incredibly similar habitat type and diet. It’s the perfect circumstance for convergent evolution. The convergences between these two completely unrelated species are incredible. Body proportion, colouration, small size, indistinct head, smooth scales, giving live birth, the colour of the tongue… From every angle this case is as striking as that of the Green Tree Python and Emerald Tree Boa. Except for the Slug Eater and Slow Worm are even more distantly related!

Eastern Indigo Snake (Drymarchon couperi) and the King Cobra (Ophiophagus Hannah)

These two are a less obvious case at first glance – but not once you take their dietary preferences into consideration.

The Eastern Indigo Snake, seen below, is the largest snake in the continental US, and one of the most impressive. When seen in person, they have an incredible blue-black sheen. They also have a stocky build that makes other colubrids look like weaklings.

Eastern Indigo Snake

This photo was provided by Black Pearl Reptiles, a specialist breeder of Drymarchon, and shows just how beautiful this species is. John at Black Pearl Reptiles has a reputation for breeding exceptional snakes. He also provides a free Drymarchon care sheet on his website.

The King Cobra is the world’s longest venomous snake, and the only species that goes to the effort of building a nest for its eggs, which it guards until they hatch. Despite their huge size and potent venom, they are responsible for few fatalities compared to species like the Russell’s Viper (Daboia russelii).

The King Cobra
Michael Allen Smith from Seattle, USA, CC BY-SA 2.0, via Wikimedia Commons

So, what on earth do these two have in common? Well, they’re both ophiaphagus (snake-eating) species which have gained an immunity to the venom of local species that they prey on. This is what I would call an example of physiological convergence.

Interestingly, exceptional intelligence has been observed in these species, with the King Cobra thought to be the most intelligent snake. Perhaps to be a good snake-eater you need to be smarter than other snakes? If that were true, then surely the Cape file snake (Limaformosa capensis) and King Snakes (Lampropeltis spp.) would also be intelligent.

This shared braininess may be a coincidence, so for now I’m going to consider venom immunity to be their only convergence.

Montpellier Snake (Malpolon monspessulanus) and Eastern Coachwhip (Masticophis f. flagellum)

Now here’s a couple that are separated by geography and phylogeny, but united by their hunting method.

The Montpellier Snake is a fast moving, diurnal, and somewhat grouchy snake that lives in southern Europe, North Africa and the Middle East. It is a rear-fanged (opisthoglyphous) colubrid that has a mild venom but poses no threat to humans. Despite this, it is often referred to as “potentially dangerous” by herpetologists. Sadly, this probably does lead to it being needlessly feared.

Montpellier Snake (Malpolon monspesselanus)
Credite: Bernard DUPONT from FRANCE, CC BY-SA 2.0, via Wikimedia Commons

The Eastern Coachwhip, on the other hand, is a non-venomous snake that flees humans as fast as it can. Notwithstanding, it has a disturbing legend surrounding it: namely that it chases you down and whips you with its tail! This is of course nonsense, but an interesting story nonetheless…

Eastern Coachwhip
Credit: Peter Paplanus from St. Louis, Missouri, CC BY 2.0, via Wikimedia Commons

As for hunting, these two snakes are visual, daytime hunters that chase down their prey and grab it with fast, accurate strikes. To help with this, they both have long, slim bodies and a head morphology that prioritises forward vision and depth perception.

In effect, they have a slim, pointed rostrum and a furrow that runs between their eyes and nostrils. This furrow makes them look exceptionally moody,  but it also allows them to target their prey more accurately. The effect from the snake’s point of view is probably similar to looking through a gun sight.

In Conclusion

Convergent evolution is a fascinating phenomenon that has occurred over and over in Squamates. The sheer number of cases like the few I’ve mentioned above make them an ideal group of animals to use as a learning aid when studying homoplastic traits.

It’s vital to understand convergent evolution to gain a better understanding of evolution in general. The mechanism is easy to understand, and you can find examples yourself. 

In the future, I’m sure we’ll notice more cases in Squamates. In the meanwhile, I’ve given you a few more examples you can use to persuade anyone that evolution isn’t “just a theory”.

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