The term ‘living fossil’ is often used to describe an organism that has, at least superficially, remained unchanged for millions of years.
While there aren’t any individual species alive today that also lived hundreds of millions of years ago, there are several groups of organisms that look a lot like their ancestors and, save for some minute changes to their DNA, are pretty much identical, not only in terms of looks but lifestyles too.
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These ‘living fossils’ are important as they provide a window into Earth’s distant past and help us to understand how some organisms have found themselves in states of evolutionary stasis, while others haven’t.
10 living fossils
Coelacanth
This prehistoric-looking fish was historically thought to be long-extinct, until a recently deceased one showed up at a fish market in Eastern Cape, South Africa, in 1938. As a group, coelacanths first appeared in the Early Devonian, around 409 million years ago, and prospered right up until the extinction event that wiped out the dinosaurs, 66 million years ago.
Now, there are only two species of coelacanth left, both of which live in deep waters and only come out of their caves at night to hunt smaller fish and squid.
Bristle worm
With more than 10,000 species currently known to science, this family of marine worms (named after the many bristles that protrude from their body segments) is incredibly diverse.
The oldest confirmed species lived during the Cambrian, about 520 million years ago, but there are several bristle-worm-like animals that may be even older. These worms use their iconic bristles for a variety of different things, including crawling, swimming, and even defence.
They’re found throughout all levels of Earth's oceans, from the surface to the abyssal plain.
Tuatara
It might look just like a lizard, but the tuatara belongs to an entirely different family of reptiles known as Rhynchocephalia. From 240 to 150 million years ago, this group dominated many of the habitats occupied by lizards today, but now they’re represented by just a single species - the tuatara, or Sphenodon punctatus.
Today, tuataras are confined to the uninhabited islands that surround New Zealand’s North Island, where large colonies of seabirds also live. Some tuataras have even been documented sharing burrows with these birds.
Horseshoe crab
Despite the name, horseshoe crabs aren't actually crabs. Instead, they belong to a diverse group of invertebrates known as the chelicerates, which includes spiders, scorpions, ticks, and mites.
Unlike other chelicerates, which demonstrate quite a lot of diversity through time, today’s horseshoe crabs look morphologically identical to those that lived during the Early Triassic, circa 250 million years ago. They occupy the same niches too, scuttling through silty seabeds in search of worms, molluscs, and other tasty invertebrates to eat.
Another interest fact about horseshoe crabs is that the Atlantic horseshoe crab Limulus polyphemus wins the award for animal that has saved the most lives - thanks to its blue blood.
Platypus
This bizarre, egg-laying animal, that looks like a cross between a duck and a beaver, actually belongs to an ancient group of mammals known as the monotremes. This group is now represented by just the platypus and the echidna, but during the time of the dinosaurs - roughly 100 million years ago - they were reasonably diverse.
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A lot of early monotremes looked similar to their living descendants, with strange beaks, squat bodies, and paddle-shaped tails. Like today’s platypuses, many of them were also semi-aquatic (e.g. Steropodon).
Lamprey and hagfish
Nearly all vertebrates alive today have jaws, aside from lamprey and hagfish. These slender, eel-like creatures have funnel-shaped mouths that are lined with dozens of tiny, barb-like teeth.
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Lampreys originated in the Late Devonian (around 360 million years ago), while hagfishes emerged about 50 million years later in the Late Carboniferous. They may be the only jawless vertebrates alive today, but from 485 to 420 million years ago jawless vertebrates like them dominated many underwater ecosystems, outcompeting a lot of early jawed vertebrates.
Snapping turtle
For the last 70 million years, snapping turtles have remained virtually unchanged. This family of reptiles, known as Chelydridae, has an impressive fossil record, with species documented from several periods from the time of the dinosaurs to the present day.
These extinct snapping turtles looked just like modern species; they also had long tails, ridged shells, and deadly-looking beaks. Like today’s snapping turtles, those that lived alongside the dinosaurs were probably also capable of crunching through bones.
Okapi
This half-zebra, half-giraffe hybrid is endemic to the canopy forests that are found in the north Democratic Republic of the Congo in central Africa. Together with giraffes, okapis are the last living members of a once diverse family known as Giraffidae.
This group can trace its roots back to the Miocene (~20 million years ago) and several animals that looked very similar to today’s okapis, such as Samotherium and Sivatherium. Whether or not these giraffids also ate bat droppings for additional nutrients, like okapis do, is unclear.
Nurse shark
At about 112 million-years-old, the nurse shark (Ginglymostoma cirratum) is widely considered to be one of the oldest, if not the oldest living vertebrate species.
While most ‘living fossils’ are contemporary species that superficially resemble their ancient relatives, today’s nurse sharks are so similar to those that lived during the Cretaceous that they’re considered the same species. They’re amongst the calmest species of shark and typically swim along the seafloor, sucking up small fish with their vacuum-like mouths.
Horsetail
Not all ‘living fossils’ are animals, some types of plants have also stood the test of time, survived several extinction events, and made it through to the present day.
The invasive weed known as horsetail (Equisetum) is one of those plants, emerging around 185 million years ago and 55 million years before the first ever flowering plants. These early horsetails formed dense forest understories that provided shelter and food for many groups of animals, including dinosaurs. Now, horsetails grow almost anywhere, from meadows to the sides of motorways.