10 “Living Fossils” That Have Survived Mass Extinctions And Have Barely Changed in Millions of Years
Most creatures on Earth evolve constantly but these have hardly changed after millions of years.
by Tibi Puiu · ZME ScienceThe term “living fossil” might sound contradictory, yet it’s a phrase that perfectly captures the strange reality of certain ancient species. Even after millions of years, they seem to have barely changed. Exceptional species like these offer a window into the Earth’s evolutionary past, preserving body structures, survival strategies, and genetic codes. And all of these have weathered epochal changes in our planet’s climate, landscape, and ecosystems including mass extinctions, like the one that wiped out the dinosaurs and 70% of all vertebrate species.
Most creatures on Earth evolve constantly, developing new traits that help them survive in their changing habitats. But for some, like the coelacanth, and the gingko tree, evolutionary change has been relatively limited. Instead, these species seem almost frozen in time, many of their physical forms holding patterns more ancient than the dinosaurs.
It’s not that they were immune to evolution. There have been genetic tweaks and subtle shifts. But, compared to the roaring river of change that drives other species, theirs is more like a slow trickle.
Here are just ten of the most interesting living fossils out there.
1. The Horseshoe Crab
A walk along the shores of Delaware Bay might reveal hundreds of these helmeted arthropods crawling along the sand, seeking a mate or laying eggs. Fossil records of horseshoe crabs date back over 450 million years, long before dinosaurs walked the Earth. Astonishingly, they look quite similar to their ancient ancestors. This evolutionary stability is owed to a near-perfect alignment with their environment, which has allowed these armored creatures to thrive in much the same way as they always have.
Horseshoe crabs belong to a unique class known as Merostomata. Despite their name, they are more closely related to spiders and scorpions than to true crabs. The structure of their body is divided into three main parts: a hard, domed shell (called the prosoma) that protects their front half, a narrow middle segment, and a long, rigid tail spine known as a telson. This iconic body shape has remained virtually unchanged since the Ordovician period.
2. Crocodilians (Crocodiles and Alligators)
Crocodilians — comprising crocodiles, alligators, caimans, and gharials — are among Earth’s most formidable living fossils. Although they look remarkably similar to their prehistoric ancestors, these modern-day predators have outlasted species after species through cunning survival strategies and incredible adaptations.
Crocodilians first appeared roughly 95 million years ago during the Late Cretaceous period, a time when Tyrannosaurus rex and Triceratops roamed. Fossils of ancient crocodilians show a remarkable similarity to the crocodiles and alligators we know today. With their armored skin, powerful jaws, and unparalleled stealth, they were built to thrive in aquatic and semi-aquatic environments.
They appear to have stumbled upon a winning formula early in their evolutionary journey and held fast. When an asteroid struck Earth about 66 million years ago causing widespread extinction, crocodilians survived. Scientists believe their survival is due in part to their cold-blooded biology and their semi-aquatic lifestyle. These enable them to survive long stretches without food and to access food sources from both water and land.
3. Lampreys
It has no jaws and no bones. Its mouth is shaped like a sinister suction cup lined with rows of sharp, hook-like teeth. This is the lamprey — a living fossil from an era before fish developed jaws and a creature whose existence spans over 360 million years, offering glimpse into one of the earliest vertebrate lineages on Earth.
Lampreys belong to a group known as Agnatha, or “jawless fish,” a class that flourished in the ancient seas long before the first land vertebrates. When we think of evolution, we often picture creatures gradually developing more sophisticated structures over millions of years. Yet, the lamprey stands as a testament to the strength of an ancient, minimalist design. Its body structure is so effective that it has remained largely unchanged through the rise and fall of ecosystems. Even as jawed fish became dominant and vertebrates began to conquer land, it remained.
Today, lampreys continue to intrigue scientists not only because of their ancient lineage but also because of the insights they offer into vertebrate evolution. Their life cycle, with a prolonged larval phase resembling early vertebrate ancestors, provides a snapshot of very early evolution. Studying lampreys has even helped scientists uncover clues about the origins of spinal cords and complex neural systems. This is because these creatures possess some of the most basic neural structures among vertebrates.
4. Scorpions
The scorpion has roamed Earth’s landscapes for over 400 million years, evolving through eons while keeping much of its primeval design intact. Scorpions are true living fossils, relics from a world far older than the first trees and vertebrate land-dwellers.
Scorpions first appeared during the Silurian period, around the same time as the first terrestrial plants. Back then, Earth’s surface was a barren landscape punctuated by small, hardy shrubs and few animals. These early scorpions were likely aquatic, resembling modern-day scorpions but adapted to life in the seas. As life on Earth began to venture onto land, scorpions were among the first predators to follow.
Even now, scorpions are found in some of the most inhospitable regions on Earth, from the blistering sands of the Sahara to the frigid peaks of the Himalayas. Their hard exoskeletons provide them with an armored defense against both predators and the elements, while their ability to slow their metabolism allows them to survive on remarkably little food and water. Some scorpions can go for up to a year without eating, a trait that likely served their ancestors well during mass extinctions.
5. Cockroaches
Long before they became urban survivors, cockroaches were thriving in ancient rainforests alongside massive amphibians and early reptiles, with fossil records tracing their existence back over 300 million years to the Carboniferous period. These creatures have witnessed tectonic shifts, ice ages, and mass extinctions. All the while, they maintained a design so robust that it has weathered each turn in Earth’s evolutionary saga.
The ancient cockroaches, known as blattodeans, bear a striking resemblance to today’s roaches. Fossils show that they had similar flat, oval bodies, long antennae, and a capacity to flatten themselves to squeeze into tight spaces. Unlike today’s roaches, however, early cockroaches had external ovipositors for laying eggs and some sported effective wings — traits that have gradually disappeared or diversified over millions of years.
6. Nautilus
Often called the “living fossil of the sea,” the nautilus has maintained its form for eons since it first appeared nearly 500 million years ago. This ultimate survivor embodies the phrase “if it isn’t broken, don’t fix it.”
The nautilus belongs to a family known as Nautilidae, a group of shelled cephalopods that once thrived in ancient oceans. They shared the seas with early arthropods, giant trilobites, and strange armored fish. Unlike its close relatives — the squid, octopus, and cuttlefish — the nautilus has retained a hard, protective shell.
As the animal grows, the shell develops new chambers in a logarithmic spiral — the golden ratio. Each chamber contains gas, allowing the nautilus to control its buoyancy and glide effortlessly through the depths, a natural submarine perfected through millennia.
Fossil records show that the nautilus of today is almost identical to those from hundreds of millions of years ago. This is a feat of evolutionary stasis that few species can claim. Scientists attribute this lack of change to its specialized habitat and lifestyle. Deep in the twilight zone of the ocean, the nautilus avoids many of the intense evolutionary pressures faced by surface-dwelling creatures. Its habitat, largely free from predators and competitors, has allowed it to retain its ancient design without the need for drastic adaptations.
7. Coelacanth
When the coelacanth was discovered in 1938 in South Africa’s coastal waters, it shocked scientists. This was a creature that was supposed to have gone extinct along with the dinosaurs. But here it was, back from the dead. The coelacanth’s reappearance from evolutionary obscurity was like something out of a biological time machine. Of course, it had never gone extinct — we just didn’t know where to look for it.
Coelacanths belong to a lineage that traces back roughly 400 million years to the Devonian period. It was a time when Earth’s oceans teemed with strange and diverse creatures. For years before its rediscovery, scientists only knew of coelacanths through fossils, showing they were among the earliest lobe-finned fish. This is the group that eventually gave rise to the first land-dwelling vertebrates.
Unlike modern fish, whose fins are rays attached directly to their bodies, coelacanth fins are supported by bony, limb-like structures. This gives them a unique flexibility. Some scientists believe these fins represent a key transitional step in the development of vertebrate limbs — one of the ancient designs that allowed vertebrates to explore the shorelines and eventually conquer the land.
8. The Tuatara
With its scaly skin, beak-like mouth, and a distinctive “third eye” atop its head, the tuatara is no mere lizard. This ancient creature belongs to an evolutionary lineage that diverged from all other reptiles around 250 million years ago.
It is the last survivor of a group of reptiles known as Rhynchocephalia. In the Triassic period, rhynchocephalians were widespread, with species ranging across many continents and niches. However, as dinosaurs diversified and other reptiles evolved, this group gradually disappeared. Soon only the tuatara’s lineage remained to carry on their legacy.
One of the most striking aspects of the tuatara is its slow, steady pace of life. These reptiles are built for longevity, with some individuals living over 100 years. Their metabolism is incredibly slow — even for a reptile. And so, they conserve energy and endure long periods of low activity during New Zealand’s cooler seasons.
Perhaps the tuatara’s most mysterious feature is its “third eye,” a light-sensitive organ located on top of its head. This organ, called a parietal eye, is covered by scales in adulthood but is visible in young tuataras as a small, translucent patch. Scientists believe the parietal eye plays a role in regulating circadian rhythms and seasonal behaviors, though its exact function remains unclear.
As far as the “living fossil” designation is concerned, the tuatara’s status has been highly debated. However, a 2017 study indicated that tuataras do, in fact, meet both of the generally agreed conditions for being a living fossil. They show a significantly slower rate of physical evolution and are “morphologically conservative.” The latter term is just another way of saying that any visible changes that did occur were subtle and not much of a deviation from Tuatara Model 1.0.
9. Komodo Dragon
The Komodo dragon, with its muscular body, serrated teeth, and a venomous bite, is the world’s largest lizard — but it’s also a living echo of ancient megafauna. These formidable creatures, which can reach over 10 feet in length and weigh up to 150 pounds, are the apex predators of the volcanic islands of Indonesia, a role rarely occupied by reptiles.
The Komodo dragon’s lineage goes back roughly 100 million years, to the time when large monitor lizards first began to spread across what is now Africa, Asia, and Australia. Fossil evidence shows that they belong to a group of monitor lizards called Varanidae, a lineage that once included even larger relatives. While most monitor lizards are relatively small and have evolved to occupy various ecological niches, the Komodo dragon has retained a size and ferocity that recall the megafaunal predators of the past.
10. Aardvark
With a pig-like snout, long ears, and a body built for digging, the aardvark cuts an odd figure, resembling a mix between a pig, a rabbit, and a kangaroo. But appearances can be deceiving. The aardvark belongs to an ancient lineage that diverged from other mammals tens of millions of years ago.
As the sole survivor of its order, Tubulidentata, the aardvark offers a rare link to a distant past, embodying traits and habits honed in a world long gone. Fossils trace their lineage back around 55 million years, shortly after the extinction of the dinosaurs, during a time when mammals were diversifying into new and varied forms. Unlike most other African mammals that belong to the more closely related groups of carnivores, herbivores, or primates, the aardvark branched off early and developed highly specialized traits suited for survival in an insect-rich ecosystem.
The strongest proof that the aardvark has evolved very little across millions of years lies in its DNA, with a genetic makeup that has stayed relatively unchanged since the lineage first appeared.