Snakes and eels – two slippery, elongate creatures that inhabit both land and water. At first glance, they appear quite similar, leading many to wonder: are snakes and eels related? This is an intriguing question with an answer that delves into evolutionary biology.

If you’re short on time, here’s the quick answer: snakes and eels are not closely related. While they share some superficial similarities like their elongated bodies, they evolved these traits independently and belong to different taxonomic groups.

In this approximately 3000 word article, we’ll take a detailed look at the evolutionary relationship between snakes and eels. We’ll compare their anatomy, habitats, reproductive strategies and more. We’ll examine the evidence from fossil records and DNA analysis that sheds light on how these two groups are connected in the tree of life.

By the end, you’ll have a clear understanding of how snakes and eels converged on some similar adaptations despite their distant relationship.

The Classification and Phylogeny of Snakes and Eels

Snakes Belong to the Reptilia Class

Snakes belong to the biological class Reptilia, which includes lizards, turtles, crocodiles, and tuatara. Reptiles are characterized by scales or scutes, ectothermy (cold-blooded), and laying soft-shelled eggs on land.

Snakes evolved from lizard-like ancestors in the Late Cretaceous period about 100-80 million years ago.

There are over 3,700 species of snakes in the suborder Serpentes. Snakes have elongated, legless bodies covered in overlapping scales. They have flexible jaws to swallow large prey and a highly developed sense of smell and vibration detection. Snakes use a variety of venom proteins to immobilize prey.

Some common snake families are pythons, boas, vipers, and cobras.

Eels are Fish in the Actinopterygii Class

In contrast, eels belong to Actinopterygii, the class of bony, ray-finned fish. There are over 800 species of freshwater and marine eels in 16 families. Eels have elongated, snake-like bodies with fins, gills, and mucus-secreting skin.

They hatch from eggs then transform into their adult form through metamorphosis. Some key features distinguishing eels from snakes include:

Eels Snakes
– Cold-blooded vertebrates – Cold-blooded vertebrates
– Fish (aquatic) – Reptiles (terrestrial)
– Breathe through gills – Breathe through lungs
– Have fins – Lack limbs
– Lay eggs in water – Lay eggs on land
– Scales contain mucus – Scales are dry

The most obvious difference is that eels live their whole lives underwater as fish, while snakes evolved from land-dwelling lizards and only some species like sea snakes have adapted to marine environments.

Genetically, eels are classified taxonomically in the bony fish clade Teleostei, while snakes belong to the reptile clade Squamata.

Anatomical Differences Between Snakes and Eels

Snake Anatomy

Snakes have elongated, limbless bodies covered in scales. They have a solid skull with flexible jaws that allow them to consume prey larger than their head. While snakes don’t have eyelids, they do have an outer transparent scale that protects their eyes.

Most snakes use their forked tongue and Jacobson’s organ to detect chemical cues for sensing prey. Internally, they have a very flexible spine and numerous ribs for compressing and expanding their bodies.

Eel Anatomy

Like snakes, eels have elongated, scale-covered bodies without limbs. However, eels have gill slits on each side of their heads that allow them to breathe underwater. Their skull is made of flexible cartilage rather than bone.

While many eels live in freshwater or saltwater habitats, some species are able to migrate on land for short distances by wiggling. Eels tend to have small pectoral fins and lack the heat-sensing pits found in certain snakes.

Key Anatomical Differences

While snakes and eels share some common anatomical traits, there are several key differences:

  • Snakes have rigid skulls, while eels have more flexible, cartilage-based skulls
  • Eels have gill slits for underwater breathing; snakes do not have gills
  • Eels have pectoral fins; snakes do not have fins or limbs of any kind
  • Some snakes have heat-sensing facial pits; eels lack these specialized sensory organs

So while both creatures have elongated bodies adapted for burrowing and swimming, eels are uniquely equipped for aquatic life with gills and fins. Snake anatomy shows more adaptations for terrestrial habitats, prey detection, and swallowing larger animals due to their rigid skulls and sensory systems.

Characteristic Snakes Eels
Body covering Scales Scales
Skull composition Solid bone Flexible cartilage
Gills No Yes
Fins No Pectoral fins present in some species
Heat sensing Facial heat pits in some species No

Habitat and Behavior

Snakes inhabit a wide variety of habitats around the world. As ectotherms that rely on external heat sources to regulate their body temperature, snakes are found in tropical, subtropical, temperate, and semi-arid environments.

Some species thrive in deserts, grasslands, forests, swamps, marshes, streams, rivers, lakes, and oceans. Snakes can be found from sea level up to elevations over 14,000 feet. Their ability to adapt to diverse habitats contributes to snakes being one of the most geographically widespread groups of vertebrates.

Snakes exhibit a variety of behaviors and adaptations that enable them to survive and thrive. Being carnivores, snakes are excellent hunters. Many species rely on camouflage and patience to ambush prey. Some snakes, like boas and pythons, are constrictors that squeeze their prey to death.

Other snakes have highly toxic venom used to kill and subdue prey. Snakes flick their forked tongues to pick up chemical cues and identify predators, prey, and mates. Shedding their skin periodically allows snakes to grow and remain healthy.

During cold winters, some temperate species brumate underground in communal dens until spring emerges.

When it comes to reproduction, most snakes lay eggs while some species give live birth. Female snakes incubate their eggs internally until they are ready to hatch. Parental care is minimal if present at all.

Young snakes are independent from birth and must rely on innate skills to hunt, avoid predators, regulate their temperature, and find suitable habitat.

Snake Habitats and Behaviors

Eels primarily live in shallow waters and oceans near coastlines, though some tropical species inhabit freshwater rivers and lakes. Their slender, flexible bodies allow them to hide in small crevices and burrow in mud or sand.

Being nocturnal, eels emerge at night to hunt and forage while spending the daytime resting in their shelters.

Eels are carnivorous and eat a variety of prey including fish, crustaceans, worms, and mollusks. They ambush prey or actively hunt by smelling and sensing electrical fields. Their jaw structure enables them to swallow prey whole regardless of size.

Some larger species even prey on birds and small mammals.

When it comes to reproduction, eels have a unique catadromous life cycle. They spawn far out at sea in deep waters, and larvae drift on ocean currents for months or years before reaching coastal nurseries.

Young eels transform into their adult forms in fresh or brackish waters, feeding and growing for 5-40 years before returning to the sea to spawn.

Contrasting Lifestyles Despite Some Overlap

While snakes and eels fill similar ecological niches as carnivorous, elongated fish-like creatures, they lead very different lifestyles. Snakes have adapted to living on land, while eels remained aquatic.

The key differences emerge from structural adaptations that equip each group for survival in their respective habitats.

For example, snakes evolved scaly skin, lack of fins, and ventral scales for terrestrial locomotion. Eels retained fins and mucus-covered skin without scales or ventral scutes. While snakes breathe air with lungs, eels have gills throughout life for absorbing oxygen from water.

The differences even extent to their means of propulsion – lateral undulation in snakes vs anguilliform locomotion in eels.

However, despite their habitat differences, snakes and eels converge in some similarities like being carnivorous, having elongated bodies, living solitary lives, and having a dramatic metamorphosis at birth. But these are relatively superficial similarities stemming from their shared ancestry.

The evolutionary divergence between the clades reflects their profound habitat differences. Still, snakes sometimes enter water and eels occasionally come on land for brief periods. So while they mostly live apart, snakes and eels still overlap some in their habitat usage and lifestyle.

Reproduction and Life Cycles

Snake Reproduction

Most snakes reproduce sexually, with males having a pair of copulatory organs called hemipenes that are stored inverted in the base of the tail and turn outwards during mating. Fertilization is internal, with the male snake depositing sperm inside the female.

Some snake species can store sperm for long periods before the eggs are fertilized. Gestation periods vary greatly between species, ranging from 1-2 months up to 6-10 months. Most snakes are oviparous, meaning they lay eggs, though some species are ovoviviparous and give birth to live young.

Snake eggs can number anywhere from 3-50 per clutch depending on species. Eggs are often hidden in warm, humid locations to incubate. Hatchlings are independent from birth. Snakes reach reproductive maturity around 2-4 years old.

Their mating seasons usually align with the seasons – in spring, summer or autumn when prey is abundant.

Eel Reproduction

Most eels reproduce through external fertilization, releasing sperm and eggs into the water during spawning events that involve large numbers of eels gathering together each year. Spawning areas are often far from adult eel habitats.

The European eel, for example, migrates over 3,000 miles to the Sargasso Sea to spawn.

Eel eggs float near the ocean surface and hatch into flat, transparent larvae that drift in currents for up to three years before metamorphosing into glass eels and then elvers. Elvers swim back to coastal waters and into freshwater streams, where they grow and mature.

Freshwater eels migrate back downstream to spawn after 5-20 years, while marine eels like congers spawn annually or biennially. Most eels die after spawning.

Vastly Different Reproductive Strategies

Snakes and eels have vastly different reproductive strategies. Snakes are carnivorous reptiles that retain their eggs internally to incubate before giving live birth to young that are immediately independent.

Though some sea snakes and marine eels give birth to live young, most eels release eggs and sperm into the water to spawn.

While snakes reach maturity in just a few years, freshwater eels undergo long migrations to remote spawning grounds after up to twenty years in rivers and lakes. Their larvae then drift ocean currents for years before migrating back to coastal habitats.

These incredibly different life cycles highlight how evolution has shaped their reproduction around their ecological niches.

Statistics from the Animal Diversity Web show snakes have an average gestation period of 3-4 months and clutch sizes around 12, while freshwater eels migrate thousands of miles to spawn after 5-20 years of maturity.

Truly snakes and eels could hardly be more different when it comes to making more snakes and eels!

Evolutionary Origins and Fossil Evidence

The Evolutionary History of Snakes

The evolutionary origins of snakes date back around 100-125 million years ago to the mid-Cretaceous period when lizards began adapting to fossorial (burrowing) environments. These ancient snakes evolved from lizards and were likely small, burrowing creatures that still had vestigial leg bones called hindlimbs, similar to modern day boas and pythons.

Over millions of years, ancestral snakes lost their legs entirely as they specialized for subsurface movement and hunting. By comparing fossil records and DNA analysis, scientists found that all living snakes evolved from a common ancestor.

The overriding theory is that snakes share ancestry with an ancient line of aquatic lizards called mosasaurs, before adapting to land mobility.

The Evolutionary History of Eels

In contrast, the evolutionary timeline of eels stretches back much farther. The earliest known fossil eels, like Pantylus cordylus, date all the way back to the early Cretaceous period over 140 million years ago!

Unlike snakes which evolved from terrestrial lizards, eels trace their ancestry directly to primitive fish. Over tens of millions of years, these fish developed progressively more “eel-like” body shapes and structures adapted foranguilliform (eel-like) movement.

Modern eels belong to a biological order called Anguilliformes containing about 800 different eel species, whose long snake-shaped bodies allow them to hide in rocky crevices and small openings underwater.

Fossil Record Shows Distant Relationship

While snakes and eels superficially seem similar in appearance, the fossil record shows they actually evolved very far apart from totally different ancestors. Snakes share recent common ancestry with mosasaurs and ancient land lizards, while eels trace all the way back evolutionarily to some of the first fish species in the oceans.

Their extreme divergence is why most scientists do not consider snakes and eels to be closely related at all. In fact, some analyses indicate snakes are more closely related genetically to monitor lizards and iguanas than they would be to any species of eel!

However, a few very unique eel species like snipe eels and gulper eels display odd traits and adaptations that blur the lines between fish and reptile-like appearances. So while they lack an actual close evolutionary relationship, snakes and some eels outs our certainly converged via parallel evolution to fill similar niches at different periods of Earth’s history.


In summary, while snakes and eels share common traits like their elongated, limbless bodies, they are only distantly related evolutionary speaking. Snakes are reptiles that evolved on land, while eels are fish that evolved in the sea.

Examining their anatomy, habitat, reproduction and evolutionary history makes it clear these groups are not closely related, despite some superficial similarities. So the next time you see a snake or eel, you can marvel at their unique adaptations while knowing they came about on completely different branches of the tree of life.

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