No individual species alive today was around during the age of the dinosaurs, between 246–66 million years ago. But there are several groups of species currently roaming the Earth who can trace their roots back to ancient ancestors that would have looked remarkably similar.
For these organisms – so-called ‘living fossils’ – time has almost stood still. That’s not to say they’re entirely unchanged, however; their DNA is distinct and has been put through the evolutionary wringer many times.
These living fossils give us a glimpse into what life was like millions of years ago. They also show us just how resilient some groups have been to calamitous, prehistoric events that have consigned others – such as the dinosaurs, for example – to extinction.
1. Crocodilians
There are more than two dozen species of crocodilians alive today, including true crocodiles, alligators, caimans and gharials. These extant crocodilians share a common ancestor that lived alongside the dinosaurs in the Late Cretaceous, about 80 million years ago (Mya).
This common ancestor looked a lot like today’s crocodilians and, like them, spent most of its time hanging out at the water’s edge, soaking up the sun and waiting for unsuspecting prey to enter its domain.
While they may look unchanged after nearly 80 million years, today’s crocodilians are a far cry from their distant ancestors, which first appeared in the Late Triassic, around 235 Mya. These extinct, crocodilian relatives were considerably more diverse than their modern descendants.
Some, like Litargosuchus, were built like whippets and pursued small prey on land much like wolves, while others, such as Sarcosuchus, (illustrated above) grew to colossal lengths of up to 12m (almost 40ft) and snatched elephant-sized dinosaurs from riverbanks.
This diversity – particularly among crocodilians’ early ancestors – has led some scientists to argue that ‘living fossil’ is an inappropriate label for this group. Yes, today’s crocodilians may look prehistoric, but they’ve come a long way since their ancestors’ origins in the Late Triassic and may continue to diversify as climate change forces them to adapt.
2. Horseshoe Crabs
Despite their name, they’re not actually crabs and share more similarities with spiders, ticks and scorpions than their crustacean namesakes.
Their ancestors first appeared in the Late Ordovician, around 445 Mya, though the modern group – Limulidae – didn’t get started until the Early Triassic, around 250 Mya. Still, that makes today’s horseshoe crabs older than dinosaurs.
For the best part of 250 million years, horseshoe crabs have been in a state of ‘morphological stasis’, displaying little anatomical change. If you compared a fossilised specimen with a living one, you’d assume it was the same animal.
Their lifestyles are unchanged too – just like their ancestors, today’s horseshoe crabs can be found in silty seabeds hunting small worms and molluscs.
These creatures have dodged several mass extinctions, including the asteroid-induced destruction that wiped out the dinosaurs. It’s thought that their tolerance to extreme conditions, such as low oxygen levels, is what has made them resilient to extinction.
3. Cedar wood wasps
This diminutive, 1cm-long (0.3in) wasp is the only remaining species from a family of wasps that, during the Middle Jurassic, about 165 Mya, boasted nearly 50 species.
Today’s cedar wood wasps, Syntexis libocedrii, are endemic to the mountains of central California (USA) and British Columbia (Canada), but their ancestors were found across Eurasia – a landmass that, at the time, lay closer to North America and was loosely connected by a series of islands.
Cedar wood wasps are known for laying eggs in recently burnt cedar wood. Once they hatch, cylindrical larvae emerge and begin boring into the wood, eating it as they go. They spend up to three years in this larval stage before emerging as adults in the last few days of their lives.
Their life cycle is inextricably linked with wildfires and sightings are often made by firefighters. A study on cedar wood wasps found that they’re capable of producing large populations post-wildfire – big enough to wreak significant economic damage on stocks of cedar wood.
4. Tuatara
As dinosaur diversity exploded during the Early Jurassic, around 200 Mya, another group of scaly, lizard-like creatures began to thrive. These were the Sphenodontids, a once highly diverse family of reptiles now represented by one species, Sphenodon punctatus, or tuatara.
Tuataras closely resemble lizards, sharing similarly scaly skin, splayed limbs and clawed hands/feet, but they’re not directly related. Instead, they share a common ancestor that lived about 250 Mya just after a devastating extinction event known as the ‘Great Dying’.
Today, tuataras are found on several small, uninhabited islands that surround New Zealand’s North Island. They share these islands with burrowing seabirds and sometimes use these birds’ burrows for shelter.
The guano produced by these seabirds helps maintain huge populations of beetles, crickets and snails, which tuataras feed on.
Like some lizards, tuataras have a third eye, known as a parietal eye, on top of their heads. In adults, this eye is covered by opaque scales, but it can be seen in hatchlings. It’s likely tuataras use their third eye to regulate their circadian rhythms and aid thermoregulation.
5. Platypus
It was Charles Darwin who coined the term ‘living fossil’, when he discussed the semi-aquatic, egg-laying mammal platypus in his famous work, On the Origin of Species.
Like its original discoverers in the late 1700s, Darwin was flummoxed by this bizarre creature and described it as being so different from other Australian mammals that “two distinct Creators must have been at work.”
Unlike other mammals, platypuses lay eggs. They also have duck-like bills and, on the hind legs of males, venomous spurs. Their bills are packed with thousands of electroreceptors that they use to detect movement in their murky habitats. They also use their bills to sift through muddy river bottoms, hoovering up shrimps, worms and crayfish.
Adult platypuses are toothless, but babies are born with small teeth that are later reabsorbed into their bills. These baby teeth have helped palaeontologists trace their evolutionary lineage back through time.
Along with their closest living relatives, echidnas, platypuses are the last survivors of an early group of mammals known as the Monotremes. This group branched away from its mammalian cousins, the Marsupials (kangaroos, koalas and wombats) and the Placentals (whales, elephants and humans), at some point in the Middle Jurassic, about 170 Mya.
6. Lungfish
Slender and worm-like, with limb-like fins and gummy smiles, these fish belong to an ancient group that appeared in the Early Devonian, over 410 Mya. This is a period marked by the emergence of two major types of bony fish: the ray-finned fish and the lobe-finned fish.
Like other lobe-finned fish, lungfish have appendages that resemble limbs, as well as lungs that allow them to breathe air and survive periods of drought.
While ancient and largely unchanged after hundreds of millions of years, lungfish are far from ‘primitive’. Their lungs are divided into many smaller air sacs, maximising the surface area available for gas exchange. Most modern lungfish have two lungs, with the exception of the Australian lungfish, which has just one.
Today, there are six known species of lungfish, living across Africa, South America and Australia. Unlike their ancestors, modern lungfishes are confined to freshwater environments.
In the Devonian Period, lungfish were found all over the world and lived alongside many of their close, lobe-finned cousins, including the tetrapods that would later go on to conquer the land and diversify into amphibians, reptiles, dinosaurs, birds and mammals.
7. Horsetails
It’s not just animals that evolve, diversify and ultimately face decline or extinction. Of the roughly 380,000 species of plants known today, only a few can claim to have seen the rise and fall of the dinosaurs, as well as the transformation of the mammals – from arboreal pipsqueaks to walking, talking apes.
Equisetum, or horsetail, is one of these ancient plants. Its modern form, which looks similar to bamboo with its tall, hollow stems and horizontal bands, emerged around 185 Mya and 55 million years before the first flowering plants.
These Early Jurassic-aged horsetails formed dense forest understories, providing shelter and food for many species of dinosaurs. Analyses of the scratch marks on hadrosaurs’ teeth show that hard plants like horsetails made up a large part of their diet.
Unlike the other living fossils, horsetails are found all over the world and are considered invasive in many countries, including in the UK.
As incredibly adaptable plants, impervious to many common diseases and pests, they spread rapidly, and quickly form dense carpets that crowd out other plants. It’s no wonder they’ve survived so long.
Coelacanth
For close to 100 years, these elusive, prehistoric-looking fish were known only from fossils and were thought to have become extinct at the same time as the dinosaurs 66 million years ago.
In 1938, while perusing fishermen’s catches at a local market in Eastern Cape, South Africa, museum curator Marjorie Courtenay-Latimer discovered a freshly caught coelacanth, resurrecting a group scientists had long thought was lost to time.
Today, there are only two known species of coelacanth, but from their origins in the Early Devonian (409 Mya) to now, more than 100 fossil species have been described. Like other animals often labelled as ‘living fossils’, coelacanths actually exhibited quite a lot of diversity in their prime.
These evolutionary heydays fell in the Mesozoic Era (252-66 Mya) when huge varieties, like the 5m-long (16ft) Mawsonia, roamed the freshwater rivers and brackish estuaries of South America, North America and Africa.
Both species of coelacanth known today are confined to the deep waters of the West Indian Ocean, where they live in caves and only emerge at night to hunt smaller fish.
It’s thought this adaptation to relatively stable, deepwater environments is what ultimately saved coelacanths from obliteration 66 million years ago.
As well as dodging the extinction that claimed the lives of the dinosaurs, coelacanths also survived the infamous ‘Great Dying’ – an event that wiped out approximately 90 per cent of species on Earth – and two more of Earth’s ‘Big Five’ mass extinctions.
Read more: