Seemingly very little is known or understood about the evolution of snakes. They are a great mystery that will, probably, forever be left unknown. But we can gather some information from what remains in the fossil record. In this article, we’ll explore the beginnings of these fantastic species and determine what we can learn from their history.
Why Is Snake Evolution So Hard To Determine?
One of the reasons why snake evolution has been hard is because of the lack of fossil remains. Snakes, especially in prehistoric times, have tended to be small fragile creatures, which have fragile bones which tend not to preserve well.
What remains have been found tend to be of the vertebrate. Little of the skull or other areas tend to be fossilised.
Another element that might prevent us from knowing much about their evolution: it happens faster. We tend to think that humans are the most adaptable, but snakes are relatively super adaptors. They can adapt three times faster than other vertebrates, allowing them to adjust and evolve to new scenarios where other species will perish.
That is why you can find other groups that have too followed similar evolutionary paths (losing their legs) but haven’t been so successful. During the carboniferous to early Permian period, there were amphibians, which looked very similar to modern snakes. Yet the group died out very quickly.
And then there are the legless lizards you can find. While these do exist today, their success has been rather limited.
There are no known legless mammals or birds.
Despite the missing information, there are still lots of pieces of the puzzle that we can determine some information about their evolution.
Where Do Snakes Originate?
The first question is to always ask where they came from and why they developed these specific adaptations. And the answer to that is not well-known either. There are two main theories.
Snakes evolved in the ocean or from a burrowing species on land.
The evidence for either is relatively fragmented. The ocean origins seem to imply that snakes developed many of their traits, such as a streamlined body, transparent, fused eyelids, and loss of external eyelids to cope with saltwater and other challenges of living in the oceans.
However, the same adaptations can be said for burrowing.
Many species, such as Najash rionegrina, demonstrate the potential for a burrowing origin. However, at roughly the same time that the Najash genera were living in what is now South America, another three existed in the Middle East area. The problem with the Middle East groups is that this area was an ocean at the time.
But then another species Tetrapodophis amplectus, from 113 million years ago was discovered. This species had four legs and was preying on other animals living a burrowing lifestyle. A 2021 study placed this animal in a group of lizards not related to snakes, due to some of the distinctive snake features in the spine and skull. However, it is an example of the snake’s basic body plan having evolved independently 26 times (at least). Each of these times, the species has been a land-dwelling animal, often burrowing.
Snakes seem to be the ones that make it work best.
Another nail in the coffin for snakes originating in the ocean theory is the latest genetic studies. These have stated that snakes are not as closely related to monitor lizards and therefore sea-dwelling mosasaurs, as previously thought.
So generally, it is assumed that at some point in the Jurassic period, the first snake evolved from a terrestrial ancestor, one that probably borrowed and ate insects and tiny mammals. Very few probably took on a dinosaur (though movies would probably like us to believe that).
Escaping Their Limbs
Ask any child about snakes, and they will say they have no legs. In truth, this is not correct. Many snakes have vestigial legs. They have little use for movement but can be used for activities such as mating.
In general, it is accepted that snakes losing their legs happens in two stages. At one point, snakes lost their front limbs. How this happened is unknown, but there are plenty of species with no front limbs but back limbs.
Then after this, limbs gradually reduce until they become the spurs (or non-existent) as they are.
Size
Size seems to be an interesting aspect of snake evolution. Snakes during the age of the dinosaurs seemed to be tiny. There were also very few of them, a total of six groups.
It is important to note that many of the features at the end of the Cretaceous period that we associate with snakes had been set. They were limbless, with inner ears and transparent fused eyelids. One group had even evolved venom for hunting sometimes towards the end of the Cretaceous period.
But then the mass extinction event happened and the non-avian dinosaurs, along with other large reptiles died out. Snakes took advantage of this and diversified. Lots of new groups evolved and they also grew in size.
Titanoboa lived about 60 to 58 million years ago. The snake is the biggest ever to be known.
Originally it thought it would take on an apex predator role, and feed on mammals, crocodiles, and other large animals in the area. However, new research has demonstrated that the species probably ate a diet consisting mostly of fish.
Another significant extinction event occurred about 38 million years ago. And again snakes diversified. But they continued on the same body plan, evolving gently to suit new environments and lifestyles.
Some snakes have evolved mimicry to disguise themselves for safety (Milk snakes mimicking Coral Snakes) or to better hunt.
One evolution trait that continues to have developed during the past 65 million years is the jaw.
Many snakes can now use their flexible jaws to extend their mouth to fit many prey items that can be wider than them. However, many snake groups, like Wonambi from Australia that went extinct just 50,000 years ago, have limited jaw movement, though this might explain why they’ve died out when others in the same area have survived.
Final Word: The Evolution of Snakes: A Fascinating Debate
Snake evolution isn’t easy. We know more about so many other species and groups, even if they have no living relatives today. But snake fossils are rare, and as a result, we are still left wondering, how snakes came into existence. Though their ability to adapt and change makes them a fascinating group to study and keep.
