WOOL, SABRES AND BONE-CRUSHERS: AN ICE AGE MEET-AND-GREET

Woolly rhinoceros, Coelodonta antiquitatis

Travelling widely is one of the great pleasures of our age. Modern transport makes trips hither and thither much easier than in the past.

You discover new possibilities, see exciting new things and get to see the weird and wacky around the globe. As you know, I love a good museum and greatly enjoy the creativity that goes into making a compelling museum display.

There are museum displays that invite quiet contemplation.

And then there are museum displays that seem to say, “Welcome to the Pleistocene. Please keep your hands, snacks and easily punctured body parts to yourself.”

At the Shanghai Natural History Museum in China, three magnificent mammals stand together in skeletal splendour: the woolly rhinoceros, Coelodonta antiquitatis; the sabre-toothed cat, Smilodon fatalis; and the spotted hyena, Crocuta crocuta.

It is an impressive gathering of horn, fang and bone-cracking confidence. But before we imagine the three of them meeting at an Ice Age watering hole and arguing over who had the most intimidating dental plan, there is an important palaeontological detail to address.

They did not all live together.

The woolly rhinoceros and prehistoric populations of spotted hyenas inhabited parts of Eurasia, but Smilodon fatalis lived in the Americas. 

The Shanghai display brings these animals together as representatives of the Pleistocene world, not as a reconstruction of one prehistoric ecosystem. Think of it as an international Ice Age convention—everyone belongs to the same broad geological era, but they arrived from different continents.

And what a convention it is.

Image: Asset id: 2481462139. Shanghai China Jun 11th 2024: the fossil in Shanghai Natural History Museum: Woolly rhinoceros (Coelodonta antiquitatis), Saber-toothed tiger (Smilodon fatalis) and spotted hyena (Crocuta crocuta).

THE MARINE MAMMAL THAT LOOKS LIKE A HIPPO DESIGNED BY COMMITTEE

Standing in the Age of Mammals Hall at the Natural History Museum of Los Angeles County is one of the most delightfully perplexing mammals ever to paddle, wade or lumber along the Pacific coast.

At first glance, its skeleton appears almost familiar.

It has the solid, barrel-shaped build of a hippopotamus, the heavy bones of a marine herbivore, the forward-projecting teeth of an animal with very strong opinions about vegetation, and four stout limbs that look as though they might have carried it across the seafloor—or at least helped it negotiate the shallows with considerable determination.

But this is neither a hippopotamus nor a manatee.

It is a desmostylian: a member of an entirely extinct order of aquatic and semi-aquatic mammals that once lived around the northern Pacific Rim.

The museum specimen has often been identified in photographs and older references as Paleoparadoxia. 

More precisely, it is now classified as Neoparadoxia cecilialina, a close relative within the paleoparadoxiid family. Taxonomy is a living science, and fossil animals occasionally receive new names as researchers examine their skeletons in greater detail. The animal has not changed, of course. It remains magnificently deceased and entirely unconcerned about the paperwork.

Neoparadoxia cecilialina lived approximately 10.5 million years ago during the Late Miocene Epoch, when the coastline, climate and marine communities of California were very different from those we know today.

This remarkably complete skeleton was recovered from rocks of the Monterey Formation in Orange County, California. The individual was approximately 2.4 metres—or about eight feet—long when it died. Researchers determined that it was not yet fully grown. An adult may have reached approximately 2.7 metres in length, making it roughly the length of a large sofa, although considerably more difficult to arrange around a coffee table.

It may have been about eleven years old at the time of its death, though estimating the age of an extinct mammal with no perfect modern equivalent requires careful comparison and a certain amount of scientific humility.

And desmostylians demand humility.

They were such peculiar animals that scientists have debated almost every aspect of them: how they moved, how much time they spent on land, what they ate, how they were related to other mammals and whether their heavy bodies were better suited to swimming, wading or walking underwater.

Imagine a hippo, a manatee and a small elephant submitting design suggestions for the same animal.

Then imagine the committee approving all three.

Desmostylians appeared during the Oligocene and survived into the Miocene, living along the margins of the North Pacific. Their fossils have been found on both sides of the ocean, including western North America and Japan. Unlike seals, whales and sea cows, however, they left no living descendants. The entire order vanished.

That makes Desmostylia especially intriguing. We are not merely looking at an unusual extinct species; we are looking at the remains of a completely lost experiment in marine mammal evolution.

The name Desmostylia comes from Greek words referring to “bundled pillars,” a wonderfully architectural description of the animals’ extraordinary back teeth. 

Their molars were composed of clustered columns of enamel, giving them an appearance rather like bundles of tightly packed tubes.

These were not delicate little teeth designed for nibbling parsley.

They formed a powerful crushing surface, suited to processing tough vegetation. Desmostylians are generally interpreted as herbivores that fed in or near coastal waters, possibly consuming aquatic plants, sea grasses, algae or shoreline vegetation. 

Exactly what appeared on the menu remains debated because stomach contents and polite Miocene restaurant receipts have not survived.

The front of the mouth was equally impressive. Neoparadoxia had forward-projecting incisors and enlarged canine-like teeth. Combined with the deep lower jaw, they gave the skull a wonderfully strange profile.

Some reconstructions make the mouth look rather like the scoop of a small excavator.

I do not wish to suggest that Neoparadoxia was the backhoe of the Miocene, but if it had arrived at a construction site wearing a reflective vest, few of us would have questioned its credentials.

Those teeth and jaws may have helped the animal grasp, uproot or gather vegetation from the seabed. Its long snout could have been used to crop plants while its heavy body remained submerged in shallow coastal water.

The skeleton also reveals an animal built very differently from a whale or dolphin. Its limbs were still substantial and weight-bearing. Rather than being transformed into sleek flippers, they retained strong bones and distinct digits. This suggests that Neoparadoxia could support itself on the bottom and perhaps travel on land, although it would hardly have been graceful.

There is still scientific disagreement about precisely how desmostylians moved. Some studies have interpreted paleoparadoxiids as slow swimmers or bottom walkers inhabiting relatively shallow water. Their dense bones could have acted as ballast, helping them remain submerged without bobbing helplessly back to the surface.

Think of a diver’s weight belt, except the weight belt is the skeleton and removing it is not an option.

Dense bones are found in several aquatic or semi-aquatic mammals. They can help counteract the buoyancy produced by lungs and body fat, allowing an animal to remain at a preferred depth while feeding. 

Research into desmostylian bone structure suggests that different members of the group developed different degrees of aquatic adaptation.

Paleoparadoxia and its relatives possessed particularly dense bones and may have moved slowly through shallow coastal environments, hovering, paddling or walking along the bottom as they searched for food.

This was not a creature built for chasing tuna across the open ocean.

It was built to approach a bed of aquatic vegetation with patience, mass and purpose.

Its broad body, powerful shoulders and large pelvis suggest an animal capable of pushing itself through water and over uneven substrates. On land, it may have moved with an awkward, rolling gait. In the water, the same body could have been far better supported.

The result was likely an animal that looked somewhat cumbersome from our perspective but was well adapted to its own coastal world. Evolution does not work toward elegance as judged by humans. It works toward surviving long enough to reproduce.

Sometimes the result is a gazelle.

Sometimes the result is an eight-foot marine mammal that resembles a hippopotamus wearing an elephant costume over a manatee foundation garment.

For many years, desmostylians were commonly placed near proboscideans—the group containing elephants—and sirenians, which include manatees and dugongs. More recent analyses have complicated that picture, and their precise position within the mammalian family tree remains debated.

This uncertainty is not a failure of palaeontology. It is one of the reasons the science is so compelling.

Fossils preserve evidence, but rarely all of it. Researchers must compare the shapes of bones, patterns of tooth development, microscopic bone structure, geological age and evolutionary relationships. New discoveries can strengthen an old interpretation or turn it neatly on its head.

Neoparadoxia is a beautiful reminder that classification is not merely the act of attaching a label to a display. It is an ongoing investigation into ancestry, adaptation and deep time.

The museum skeleton is particularly valuable because it is so complete. Many fossil mammals are known from isolated teeth, fragments of jaw or scattered bones. A nearly complete skeleton allows palaeontologists to examine how the skull, spine, ribs, limbs and pelvis worked together.

One tooth can tell us that an animal existed.

A skeleton can begin to tell us how it lived.

The individual displayed in Los Angeles is also scientifically important because it represents one of the youngest known desmostylians. It lived near the end of the group’s long evolutionary history, shortly before these peculiar marine mammals disappeared from the fossil record.

Why did they vanish?

We do not yet have a simple answer. Changes in sea level, climate, coastal habitats, available vegetation and competition with other marine herbivores may all have contributed. As desmostylians disappeared, sirenians—manatees and dugongs—became the surviving large marine herbivores.

That does not necessarily mean that sea cows marched into the North Pacific and evicted them with tiny legal notices. Evolutionary replacement is rarely so tidy. Environmental change can alter habitats and food sources, favouring one group while placing another under increasing pressure.

Whatever happened, the desmostylian experiment eventually ended.

Today, their bones survive in Miocene marine rocks around the Pacific and in museum collections where we continue to ask questions of them.

This is why museum displays matter.

A mounted skeleton is not simply an attractive object placed in a hall for paleontological tourism. It is the visible result of discovery, excavation, preparation, anatomical study, comparison and scientific revision. It allows schoolchildren, researchers, travellers and gloriously enthusiastic fossil people to stand face-to-face with an organism unlike anything alive today.

We are accustomed to imagining marine mammals as whales, dolphins, seals, walruses, manatees and dugongs. Neoparadoxia challenges that tidy modern picture. The ancient oceans supported entire forms of mammalian life that have since disappeared.

Ten and a half million years ago, something large and heavy moved through California’s coastal waters. It lowered its peculiar head toward the bottom, used its formidable jaws to gather vegetation and carried a skeleton dense enough to help anchor it beneath the waves.

It had no way of knowing that one day its bones would stand in a museum in Los Angeles, surrounded by visitors attempting to decide whether it looked more like a hippo, a manatee, an elephant or an ambitious piece of earth-moving equipment.

The scientifically correct answer is that it was none of them.

It was a desmostylian. It was Neoparadoxia cecilialina. And it was gloriously, marvellously strange.

Sources: Natural History Museum of Los Angeles County—Vertebrate Paleontology, Smithsonian Ocean—Desmostylian locomotion and ecology, PLOS ONE—Bone structure and aquatic adaptation in Desmostylia, and Royal Society Open Science—Desmostylian fossil history.

Lead Image: Asset id: 2710687265. Los Angeles, USA 9.04.2025: Preserved skeleton of a prehistoric Paleoparadoxia fossil mammal displayed at the Natural History Museum, Los Angeles

RACCOONS: ADORABLE TINY HANDS AND QUESTIONABLE INTENTIONS

There are few creatures quite as charming—or as suspiciously competent—as the raccoon.

With its black mask, ringed tail and remarkably nimble front paws, the northern raccoon, Procyon lotor, looks rather like a small bear dressed for a burglary. This is misleading. 

Raccoons are not bears, although they belong to the same broad branch of the carnivore family tree. 

Their closest living relations are other members of the family Procyonidae, including coatis, ringtails, cacomistles, olingos and kinkajous.

Together, they form an impressive clan of climbers, fruit thieves, insect hunters and nocturnal specialists, most of which live in the Americas.

The fossil story of raccoons is surprisingly patchy. Small, forest-dwelling omnivores do not always leave us a generous fossil record. 

Their bodies are easily scattered, their habitats are not always ideal for fossilization, and they rarely have the decency to perish in large numbers somewhere convenient for future palaeontologists.

The wider raccoon family appears in the North American fossil record during the Early Miocene, more than 16 million years ago. 

By the Late Miocene, recognizably raccoon-like procyonids were padding through North American forests. Fossils assigned to the genus Procyon—the group containing living raccoons—are known from the Late Miocene and Pliocene. 

A newly described species, Procyon garberi, lived in Florida during the Late Miocene, showing that true raccoons were already experimenting with their familiar body plan millions of years before anyone invented the locking garbage bin. 

By the Pleistocene—the great Ice Age—raccoons were widespread across North America. 

Several fossil raccoons once given separate species names, including Procyon priscus, Procyon simus and the delightfully compact Procyon nanus, were later interpreted as variations of the living northern raccoon, Procyon lotor. 

If that interpretation is correct, modern raccoons were sharing the continent with mammoths, mastodons, giant ground sloths, sabre-toothed cats and dire wolves. 

Those giants disappeared. The raccoon remained.

This probably had much to do with flexibility. Raccoons are spectacularly unfussy omnivores. 

Depending upon where they live and what is in season, they may eat berries, grapes, apples, nuts, acorns, corn, insects, worms, crayfish, frogs, fish, eggs, small animals and carrion. 

They generally consume more invertebrates than vertebrates, but the governing principle appears to be: “Is this edible, and can I get my little hands on it?” 

In towns and cities, the menu may expand to include garden produce, pet food, compost and whatever treasures have been placed inside a container clearly labelled “raccoon enrichment puzzle.” In my garden, they leave the tomato plants alone but eat most everything else.

Their native range stretches from southern Canada through most of the United States and Mexico into Central America. They inhabit deciduous and mixed forests, wetlands, river valleys, coastal areas, farmland, suburbs and cities. 

Woodlands near water are particularly good raccoon country because they provide food, climbing trees and hollows for dens.

Raccoons have also been introduced to parts of Europe and Asia, including Germany and Japan, where some populations have become invasive. Their great adaptability, while admirable from a raccoon’s point of view, can create serious problems for native wildlife. Raccoons raid bird and turtle nests, compete for den sites and may carry diseases and parasites. Cute does not mean ecologically harmless. Nature is under no obligation to keep those two categories separate.

The raccoon’s scientific name, Procyon lotor, roughly means “washing procyon.” This refers to the famous habit of dipping and manipulating food in water. 

Raccoons are not necessarily washing dinner because they have suddenly become concerned about hygiene. 

Their front paws contain an extraordinary concentration of sensory receptors, allowing them to examine objects through touch. Moisture may enhance the sensitivity of the skin, helping them feel and manipulate their food.

In other words, they are not politely washing supper. They are inspecting it with wet fingers.

Each front paw has five long digits. Raccoons do not have opposable thumbs, but they can grasp, pry, turn and open objects with astonishing skill. They can manipulate latches, lift lids and occasionally solve problems that humans believed had already been solved by purchasing a more expensive garbage bin.

I had a midnight explorer who used to come for a visit and search about the place when I lived near a park. I would see signs of mischief but never the burgular.

Now, I have a family living in the tree next door. Mamma takes her kits out early in the morning to forage.

Their hind feet can rotate substantially, allowing them to climb down trees headfirst. This is an excellent adaptation for life in the forest and a deeply unsettling skill to witness at two o’clock in the morning.

Baby raccoons are called kits. They are born with faint masks and tail rings already visible, although their eyes remain closed for the first few weeks. A mother usually raises her kits alone, teaching them where to den, what to eat and, presumably, how to stand perfectly still on a fence while making prolonged eye contact with the homeowner.

Raccoons are primarily nocturnal, but I have been seeing them more and more in the day.

A nursing mother, a hungry youngster or an animal disturbed from its den may forage in daylight. As with all wildlife, however, raccoons should be admired from a respectful distance. They can defend themselves vigorously and may carry rabies in some regions.

There is something deeply impressive about an animal that survived the climatic upheavals of the Ice Age and then adapted to highways, suburbs, streetlights and wheelie bins.

The mammoths vanished. The sabre-toothed cats vanished. The giant ground sloths vanished.

The raccoon looked at the changing world, flexed its tiny fingers and said, “Interesting. Does this lid come off?”

MASSETOGNATHUS: PREHISTORIC FOOD PROCESSOR

Massetognathus pascuali

There are fossils that appear fierce. There are fossils that look dignified, mysterious or magnificently prehistoric.

And then there is this charming little Massetognathus pascuali at the Natural History Museum Abu Dhabi, displayed vertically with his head raised and his forelimbs tucked neatly before him, as though he has just spotted an old friend approaching.

“Oh, hey guys! You made it.”

His actual sex is unknown, of course, but he has such a cheerful, expectant air that I immediately began thinking of him as a little fellow waiting to greet visitors. 

His upright position is a museum display choice rather than a reconstruction of his normal posture in life. 

Massetognathus travelled on all four limbs, but the arrangement gives us a wonderfully clear view of his compact skeleton—and an unexpectedly endearing introduction to one of the most important chapters in mammalian evolution.

Massetognathus pascuali lived in what is now northwestern Argentina during the Triassic Period, roughly 235 million years ago. At that time, the continents were joined into the supercontinent Pangaea, dinosaurs were only beginning their long evolutionary rise, and true mammals had not yet appeared.

Massetognathus was not a dinosaur. It was a cynodont: a member of the great synapsid lineage that also contains mammals and their extinct relatives. More specifically, it belonged to a group of plant-eating cynodonts called traversodontids.

This does not mean that Massetognathus was our direct ancestor. Evolution is rarely a tidy ladder leading solemnly toward us. It is an exuberantly branching family tree filled with cousins, experiments and entire lineages that flourished before disappearing. Massetognathus occupied one of those neighbouring branches on the mammalian side of the ancient amniote family tree.

Still, its anatomy helps us understand the wider evolutionary world in which recognizably mammalian features were developing.

The name Massetognathus is particularly appropriate. It is derived from words referring to a “chewing-muscle jaw,” and chewing was very much this animal’s specialty. 

Unlike reptiles that simply seized food and swallowed it in large pieces, traversodontid cynodonts possessed differentiated teeth that could process vegetation inside the mouth.

At the front were incisors for nipping. Farther back were enlarged, broad postcanine teeth with complex crowns that met one another to crush and shear food. 

These expanded teeth are often described as gomphodont—essentially “molar-like”—although they were not identical to the molars of modern mammals.

This was serious dental equipment.

Massetognathus probably fed largely on the leaves, stems and other available plant material of Triassic Gondwana. Its broad skull, powerful jaw muscles and specialized teeth suggest a generalized herbivorous diet. 

Like a determined little prehistoric food processor, it could bite vegetation into smaller, more manageable pieces before swallowing it. 

Studies of traversodontid skulls and limbs estimate that the largest adults of M. pascuali may have weighed somewhere between about 17 and 40 kilograms, although younger individuals were considerably smaller. The broad range reflects both growth and the difficulty of estimating body mass in animals with no exact living equivalent.

This was not, then, a mouse-sized creature scurrying unnoticed beneath dinosaur feet. A large adult may have been closer in mass to a medium-sized dog, though built very differently: low-bodied, sturdy and equipped with a disproportionately robust head.

Dog-sized (think border collie, beagle or small Labrador) but not dog-like. Its proportions were very different. 

It had a long, low body, relatively short limbs and a large, sturdy head—so imagine something between a stocky dog and an oversized badger, equipped with broad teeth for grinding Triassic vegetation.

Its limbs also tell an evolutionary story. 

Research suggests that the forelimbs retained a posture intermediate between sprawling and fully upright beneath the body, while the hind limbs were held more directly underneath it. Massetognathus occupied a fascinating anatomical middle ground—not half reptile and half mammal, which would be misleading, but an animal with its own successful combination of inherited and newly evolving characteristics.

The preserved skeletons of Massetognathus pascuali come primarily from the Chañares Formation of Argentina. 

These rocks have yielded an extraordinary community of Triassic vertebrates, including dicynodonts, predatory cynodonts and early archosaur relatives close to the ancestry of dinosaurs.

Many Chañares animals were preserved within volcanogenic concretions. Volcanic activity produced enormous quantities of ash, and water moving across the landscape may have carried ash and sediment into low-lying areas. Animals buried in this material sometimes became enclosed within mineral-rich nodules, protecting their bones for more than 230 million years.

Massetognathus is especially valuable because numerous individuals representing different stages of growth have been discovered. These fossils allow researchers to investigate how its skull changed as the animal matured. 

Young individuals were not miniature copies of adults: their skull proportions, teeth and jaw structures altered as they grew, providing evidence about feeding, development and life history.

More recently, researchers have even looked inside the skull using neutron tomography. This non-destructive imaging technique can reveal internal spaces associated with the brain, nerves and blood vessels without requiring anyone to dismantle a priceless Triassic cynodont—which is generally considered good museum manners. 

Such studies help us to investigate sensory biology and the neurological evolution of non-mammalian cynodonts.

We cannot say exactly what covered the body of Massetognathus. 

Close mammalian relatives are often reconstructed with whiskers or fur, but direct evidence for these features in this particular animal is lacking. It may have possessed some form of hair-like covering, or it may not have looked quite as cuddly as modern illustrations suggest. 

Fossils give us bones and teeth with remarkable fidelity, but soft tissues frequently keep their secrets.

Even without an approved fluffiness rating, however, this specimen is irresistibly engaging.

Mounted upright at the Natural History Museum Abu Dhabi, the little skeleton seems to have paused in the middle of its 235-million-year journey to welcome us. 

The pose may not represent how Massetognathus stood in life, but it succeeds in doing something important: it encourages us to stop, look closely and form a connection with an animal from a world almost beyond imagining.

Behind that appealing face is a beautifully adapted Triassic herbivore. Its strong jaws and broad teeth reveal increasingly sophisticated food processing. Its limbs preserve a stage in the changing locomotion of cynodonts. Its skull contributes to our understanding of brains and senses along the broader mammalian evolutionary line.

He may look as though he is waiting for friends, but Massetognathus pascuali has actually been waiting to tell us a much larger story—one about chewing, changing bodies and the wonderfully tangled family history that eventually produced mammals.

And after 235 million years, it would be rude not to say hello.

Scientific background: body-mass and dietary study in Acta Palaeontologica Polonica, original postcranial study archived by the Biodiversity Heritage Library, and recent traversodontid research and references from the Asociación Paleontológica Argentina.

Lead Image: Asset id: 2757017201. Abu Dhabi UAE 8th Feb 2026: A Massetognathus pascuali fossil at the Natural History Museum Abu Dhabi highlights this Triassic cynodont and its role in early mammal evolution

PROBAINOGNATHUS: FROM BITE TO SOUND

Among the towering dinosaurs, enormous marine reptiles and other spectacular fossils at the Natural History Museum Abu Dhabi is a much smaller creature that tells one of evolution’s most extraordinary stories.

It is a fossil of Probainognathus, a small, predatory cynodont from the Triassic Period of Argentina. At first glance, it is not especially imposing. 

It lacks the theatrical horns of Triceratops, the banquet-sized teeth of Tyrannosaurus rex and the general architectural confidence of a sauropod.

But look closely at its skull—particularly its jaw—and you are staring at a chapter in the evolutionary history of every mammal alive today.

That includes whales, bats, elephants, shrews, platypuses, cats, dogs and the primate currently reading this article.

Tiny creature. Enormous family consequences.

BEFORE THERE WERE MAMMALS

To understand Probainognathus, we need to travel back roughly 235 million years to the early part of the Late Triassic Period.

The world looked nothing like it does today. The continents were assembled into the supercontinent Pangaea. Dinosaurs had only recently appeared and had not yet become the dominant large animals of terrestrial ecosystems. 

Crocodile-line archosaurs, early dinosaur relatives, large amphibians and a wonderful assortment of synapsids occupied the land.

Synapsids are the great evolutionary lineage to which mammals belong. They diverged from the lineage leading to reptiles more than 300 million years ago. Although older books often describe many early synapsids as “mammal-like reptiles,” this is misleading. They were not reptiles slowly deciding to become mammals. Synapsids and reptiles were separate branches of the amniote family tree.

One branch eventually produced dinosaurs and birds. Another produced us.

Within the synapsids arose the therapsids, and within the therapsids evolved the cynodonts. The name Cynodontia means “dog teeth,” although most cynodonts would not have looked particularly dog-like. The name refers to features of their teeth and jaws rather than any secret Triassic ambition to become golden retrievers.

Cynodonts included animals ranging from sturdy plant-eaters to quick little predators. Over millions of years, members of this group developed many features associated with mammals: differentiated teeth, enlarged jaw muscles, changes in the palate, more efficient breathing, increasingly upright limbs and a lower jaw dominated by a single large bone called the dentary.

The evolutionary story did not unfold as a straight march from primitive to advanced. It was a branching, experimental process involving many species, most of which left no living descendants. Probainognathus belongs to one of the branches close to the part of the cynodont tree from which mammals eventually emerged.

It was not quite a mammal. It was certainly not our direct, neatly labelled great-great-grandparent. It was a non-mammalian cynodont whose anatomy preserves a revealing combination of older and more mammal-like features.

Evolution, as usual, was tinkering.

HONEY, I MADE A NEW FRIEND: MEET PROBAINOGNATHUS

The best-known species, Probainognathus jenseni, was formally named by American palaeontologist Alfred Sherwood Romer in 1970. Its fossils were collected from the Chañares Formation in La Rioja Province, northwestern Argentina.

The name Probainognathus is generally translated as “progressive jaw,” a direct reference to the feature that made the animal scientifically important. 

The species name honours fossil collector James A. Jensen, who led the team associated with the discovery of the original material.

Radiometric dating of volcanic minerals has placed the principal fossil-bearing interval of the Chañares Formation at approximately 236 to 234 million years old. The formation had previously been regarded as Middle Triassic, but more precise dating showed that much of its famous vertebrate assemblage belongs near the beginning of the Late Triassic.

At that time, what is now northwestern Argentina lay within a volcanically active rift basin. Rivers, lakes and floodplains supported an ecosystem filled with dicynodonts, cynodonts, early archosaur relatives and some of the animals living close to the origin of dinosaurs.

Volcanic ash and sediment repeatedly entered the landscape. In some areas, animals were buried within concretions—hard masses of mineral-rich rock that formed around their remains. These deposits preserved a remarkable record of Triassic terrestrial life, including animals that would otherwise have been very easy to overlook.

Probainognathus was small, lightly built and probably no more than about half a metre long, although complete skeletons are rare and estimates vary. Its skull was only several centimetres in length. It likely moved on four legs and probably hunted insects and other small animals, perhaps taking tiny vertebrates when the opportunity arose.

In other words, it was living through one of the most dramatic periods in vertebrate evolution while pursuing the equally urgent matter of finding something crunchy for dinner.

TEETH MADE FOR BUSINESS

The jaws of Probainognathus held differentiated teeth rather than a uniform row of nearly identical pegs.

At the front were small incisors. Behind them were enlarged canine teeth, followed by postcanine teeth adapted for processing food. Some specimens show serrations on the canines, suggesting that these teeth were useful for gripping and cutting flesh.

This regional specialization of the teeth—incisors for nipping, canines for piercing and postcanines for slicing or crushing—was an important development in cynodont evolution. Mammals would take this dental division of labour to remarkable extremes.

Think of the front teeth of a beaver, the canines of a wolf and the grinding molars of a horse. Each part of the tooth row performs a different job. Probainognathus did not possess the sophisticated chewing system of a modern mammal, but its teeth were already part of that broader evolutionary experiment.

Its skull also provided space for substantial jaw muscles. Changes in the skull and lower jaw allowed cynodonts to bite more effectively and process food more efficiently. That may have helped support higher levels of activity and, in later mammalian relatives, the energetic demands associated with endothermy.

Whether Probainognathus itself had fur or maintained a fully mammal-like body temperature cannot be established directly from its bones. Some cynodont relatives probably possessed whiskers or hair-like coverings, but soft tissues are rarely preserved. 

It is tempting to reconstruct Probainognathus as a fuzzy, bright-eyed little creature. That may be reasonable, but we should acknowledge where fossil evidence ends, and our fondness for adding whiskers begins.

THE JAW THAT CHANGED EVERYTHING

The real evolutionary celebrity in this fossil is the jaw joint.

Most non-mammalian jawed vertebrates use two small bones to connect the lower jaw to the skull. The quadrate bone in the skull meets the articular bone at the back of the lower jaw.

Living mammals do things differently. Our lower jaw consists almost entirely of one bone, the dentary, which articulates directly with the squamosal region of the skull. The old quadrate and articular bones no longer serve as the main jaw hinge.

They are now inside our ears.

Over the course of synapsid evolution, the quadrate became the incus, or anvil, while the articular became the malleus, or hammer. Together with the stapes, they form the three tiny middle-ear bones that transmit sound vibrations toward the inner ear.

Pause for a moment to admire the audacity of this arrangement. Bones that once helped an ancestor bite eventually became bones that help us hear.

No engineering committee proposed this reassignment. Evolution modified existing structures over many generations, gradually changing their size, position and function.

For this transition to occur, however, the lower jaw required a new way to attach securely to the skull. 

Several groups of advanced cynodonts developed additional contact between bones around the jaw joint while retaining the older quadrate–articular connection. For a time, these animals effectively possessed a transitional arrangement involving both the ancestral jaw hinge and a new secondary contact.

When Romer described Probainognathus, he interpreted its anatomy as showing an incipient articulation between the dentary and squamosal—the bones that form the mammalian jaw joint. This interpretation inspired the name “progressive jaw.”

Later studies have complicated that tidy picture. Some researchers concluded that the additional contact may have involved the surangular, one of the smaller bones behind the dentary, rather than a fully developed dentary–squamosal joint. 

More recent research has also shown that mammal-like jaw contacts arose independently in more than one cynodont lineage.

The route to the mammalian jaw was not a single anatomical escalator travelling smoothly upward. It was more like several teams attempting renovations at once, occasionally arriving at similar solutions.

Even with those scientific revisions, Probainognathus remains valuable. Its reduced postdentary bones, enlarged dentary and changing relationships among the bones at the back of the skull capture an important stage in the broader transformation of the cynodont jaw and ear.

It reminds us that transitional fossils are not required to be perfectly halfway between two modern categories. They document populations in which anatomical systems were being reorganized, often in complicated and unexpected combinations.

WHY BECOME SMALL?

Many of the cynodonts nearest the origin of mammals were small animals. Miniaturization may have played a major role in reshaping their skulls.

A smaller animal experiences different mechanical pressures. Its jaw bones become more delicate, its food may require precise processing, and hearing higher-frequency sounds can become increasingly useful. Small nocturnal or crepuscular hunters able to detect insects rustling through vegetation would have benefited from improved hearing.

At the same time, the dentary was becoming larger and stronger while the other bones of the lower jaw were shrinking. Once the new jaw articulation could bear the forces of biting, the old joint bones were increasingly free to specialize in transmitting sound.

The transition did not happen in one species or during one convenient evolutionary afternoon. Fossils record a prolonged series of changes. Some early mammaliaforms still retained connections between their middle-ear bones and the lower jaw. Complete separation occurred later and may have evolved independently in different mammalian groups.

Probainognathus stands near the beginning of this extraordinary anatomical story—not as the finished mammalian design, but as evidence that the old arrangement was already being altered.

A SMALL FOSSIL IN A VERY LARGE STORY

The Probainognathus fossil displayed at the Natural History Museum Abu Dhabi helps place mammals within the wider history of life. The museum’s exhibits carry visitors through billions of years of planetary change, and this unassuming cynodont earns its place among the giants.

Dinosaurs often dominate our vision of the Triassic and Jurassic worlds. They were large, spectacular and considerate enough to leave bones that look excellent in an atrium. Yet while dinosaurs were beginning their long reign, small cynodonts were undergoing an anatomical transformation that would ultimately produce the mammals.

Somewhere among their branches arose the earliest mammaliaforms. Their descendants survived the end-Triassic extinction, lived alongside the dinosaurs, endured the end-Cretaceous catastrophe and eventually diversified into nearly every terrestrial and marine environment on Earth.

The remarkable thing about Probainognathus is not that it was “almost us.” Evolution does not work toward a predetermined destination, and the creature certainly did not know that we would someday inspect its jaw for clues to the origin of the human ear.

It was simply a small predator trying to survive in Triassic Argentina.

But within its skull, old bones and new relationships had begun to overlap. A lower jaw built from several bones was moving toward one dominated by the dentary. An ancestral jaw joint was being joined by new contacts. 

Bones that still helped support feeding were entering an evolutionary process that would eventually place their descendants deep inside the mammalian middle ear.

The next time you chew while listening to someone speak, consider the two systems working on either side of your skull. One allows your dentary to move against the skull. The other uses three tiny bones to transmit the sound.

Their histories are intimately connected.

And part of that history can be seen in a modest little fossil in Abu Dhabi: Probainognathus, the progressive jaw that helped reveal how mammals learned to bite—and, eventually, to hear.

References and Further Reading

Romer, A. S. 1970. “The Chañares (Argentina) Triassic Reptile Fauna. VI. A Chiniquodontid Cynodont with an Incipient Squamosal-Dentary Jaw Articulation.” Breviora 344: 1–18.

Marsicano, C. A. et al. 2016. “The Precise Temporal Calibration of Dinosaur Origins.” Proceedings of the National Academy of Sciences 113: 509–513.

Martinelli, A. G., Soares, M. B. & Schwanke, C. 2016. “Two New Cynodonts from the Middle–Early Late Triassic of Brazil and Comments on South American Probainognathians.” PLOS ONE 11: e0162945.

Anthwal, N., Joshi, L. & Tucker, A. S. 2013. “Evolution of the Mammalian Middle Ear and Jaw: Adaptations and Novel Structures.” Journal of Anatomy 222: 147–160.

University of California Museum of Paleontology. Jaws to Ears in the Ancestors of Mammals.

Natural History Museum Abu Dhabi. Official Museum Website.

Lead Image: Asset id: 2757017209. Abu Dhabi UAE 8th Feb 2026: A Probainognathus fossil at the Natural History Museum Abu Dhabi reveals an early mammal-like cynodont, offering insight into the origins of mammals

WHAT IS A FOSSIL? A MESSAGE FROM DEEP TIME

Pick up a fossil and you are holding evidence of a life.

Not merely an old rock. Not an attractive geological paperweight. Not something the Earth made solely to tempt us into climbing unstable slopes in inappropriate footwear.

A fossil is a message from the past.

It may be a bone, tooth, shell or leaf. It may be the delicate impression of a feather, the tunnel left by a burrowing animal or the footprints of a creature that crossed a muddy shoreline hundreds of millions of years ago.

It may even be fossilized dung.

The fossil record has never been overly concerned with dignity.

Together, fossils preserve the history of life on Earth: its astonishing experiments, spectacular successes, evolutionary detours and occasional catastrophes. They introduce us to organisms no human ever saw alive and to ecosystems that vanished long before our own species appeared.

But what exactly qualifies as a fossil—and how can something as fleeting as a footprint survive for millions of years?

Let us begin at the beginning.

SO, WHAT IS A FOSSIL?

Dinosaur Footprints near Tumbler Ridge, BC

A fossil is naturally preserved evidence of past life. That definition is deliberately broad because life leaves evidence in many different ways.

A fossil can be part of an organism’s body, such as a bone, tooth, shell, leaf or piece of wood. It can also be a mark made by an organism while it was alive: a footprint, burrow, feeding trail, nest or bite mark.

The organism itself does not necessarily need to be present.

This is one of the most important things to understand about fossils. We often picture a magnificent dinosaur skeleton standing in a museum, every rib neatly arranged and every tooth poised for drama. Yet complete skeletons are extraordinarily rare. Most fossils are fragments: a single tooth, part of a shell, a scrap of leaf, one vertebra or a dark smudge of carbon in the rock.

Some fossils are so small that thousands could sit comfortably on the head of a pin. Others belong to animals that stretched longer than a city bus.

All of them are evidence.

We divide fossils into two major categories: body fossils and trace fossils. The distinction is simple, but it opens the door to an astonishing variety of preservation.

BODY FOSSILS: WHEN PART OF THE ORGANISM REMAINS

A body fossil preserves part of the organism itself—or a direct impression, mould or cast of its remains.

The most familiar body fossils include:

• Bones
• Teeth
• Shells
• Exoskeletons
• Scales
• Wood
• Leaves
• Seeds
• Pollen
• Spores

Cenoceras Fossilized Shell Material

Hard parts are much more likely to enter the fossil record because they resist decay longer than soft tissues. Teeth are especially durable. A vertebrate animal may lose and replace thousands of teeth during its lifetime, greatly improving the odds that at least a few will survive long enough to become fossils.

This is one reason isolated fossil teeth are much more common than complete fossil animals. Nature produces teeth generously and skeletons only once per customer.

Shells also have an excellent chance of preservation. Ancient seafloors could accumulate the remains of countless brachiopods, molluscs, corals and other marine organisms. Over time, those shells became part of the sediment and, eventually, part of the rock itself.

The most durable portions of an organism dominate the fossil record. According to the National Park Service overview of body fossils, bones, teeth, shells, mineralized plates and wood are preserved far more frequently than skin, organs, flowers or fruit.

This creates an immediate problem.

The fossil record is not a complete census of everything that ever lived. It has a built-in preference for organisms with hard parts, those living in places where burial could occur and those fortunate enough to die under favourable conditions.

A clam living on a muddy seafloor has a better chance of becoming a fossil than a soft-bodied creature living on a windswept mountain. This does not mean the mountain creature was less important. It was simply less likely to leave us its forwarding address. We find many more of the durable creatures than we do the squishy. 

TRACE FOSSILS: WHEN BEHAVIOUR BECOMES STONE

Theropod Track, Thailand

Trace fossils preserve evidence of what an organism did rather than the organism’s actual body.

They are also called ichnofossils, from the Greek word ichnos, meaning track or trace. Scientists who specialize in studying them are called ichnologists.

Trace fossils include:

• Footprints and trackways
• Burrows and tunnels
• Trails
• Resting impressions
• Nests
• Root traces
• Feeding marks
• Bite marks
• Borings in shells or wood
• Coprolites, or fossilized dung
• Regurgitated material
• Gastroliths associated with an animal

A body fossil can tell us that an organism existed. A trace fossil may reveal what it was doing.

A line of footprints can show whether an animal walked on two legs or four. The distance between prints can help researchers estimate speed. Several parallel trackways may suggest that animals moved together, although such interpretations must be made carefully.

A burrow can reveal how an animal moved through sediment, searched for food or protected itself. Bite marks can document interactions between predator and prey. A resting impression can preserve the outline of an animal settling momentarily onto a soft surface.

Trace fossils often remain in the substrate where the behaviour originally occurred. Unlike bones, which may be carried away by water, scavengers or gravity, a burrow generally records activity at that exact location.

This gives trace fossils an extraordinary quality. They preserve moments. An animal stepped here. A worm burrowed here. Something bit this shell.

A dinosaur crossed this stretch of wet sediment, placing one foot after another beneath a sky no human would ever see. The animal continued on. The moment passed. But the ground remembered.

YES, FOSSILIZED POO IS A REAL FOSSIL

Coprolites are fossilized faeces, and they are among some of our most personal treasures.

They vary enormously in size and appearance. Some resemble pellets, spirals or lumpy stones. Others are difficult to distinguish from ordinary rock without examining their shape, contents or chemical composition.

Coprolites can preserve:

• Bone fragments
• Fish scales
• Plant fibres
• Seeds
• Pollen
• Insect remains
• Parasite eggs
• Chemical evidence of diet

They can help researchers determine whether an animal ate meat, plants, insects, fish—or almost anything unfortunate enough to fit inside it.

The difficulty lies in identifying the producer. Unless a coprolite is found directly associated with a particular animal, assigning it to a species can be challenging. Size, shape, contents and geological context may narrow the possibilities, but we must resist the temptation to point dramatically at every ancient dropping and declare, “Tyrannosaurus!”

Not every large coprolite came from the most famous carnivore available.

Still, fossilized dung offers something bones alone cannot: evidence of a meal passing through an animal’s digestive system. Coprolites are trace fossils that can provide direct clues about ancient diets.

One creature’s private moment has become everyone’s scientific business. Deep time can be terribly indiscreet.

DOES A FOSSIL HAVE TO BE TURNED TO STONE?

No. “Fossil” describes evidence of past life, not one particular style of preservation.

Some fossils are petrified or mineralized. Others preserve original material. Fossils can occur as impressions, carbon films, moulds, casts or remains trapped in substances such as amber, tar or ice.

Let us look at a few possibilities.

Permineralized Fossils

Bones and wood contain microscopic spaces. After burial, mineral-rich water may move through the sediment and deposit minerals inside those spaces.

This process is called permineralization.

The original structure may remain while its pores become filled with minerals such as silica, calcite or iron compounds. The result is denser and heavier than the original material but can preserve remarkable internal detail.

Petrified wood is a beautiful example. Its tissues may become mineralized so precisely that growth rings and cellular structures remain visible.

Replacement Fossils

In some fossils, the original biological material dissolves and is gradually replaced by minerals. The new mineral preserves the form—and sometimes even the microscopic structure—of the original organism.

It is rather like replacing a building one brick at a time while somehow retaining its shape.

Moulds and Casts

Imagine a shell buried in sediment.

The sediment hardens around it, but the shell later dissolves, leaving an empty impression. This cavity is a mould. If minerals or sediment later fill that mould and harden, they create a cast: a three-dimensional replica of the original shell.

An internal mould can form when sediment fills the inside of a shell and hardens before the shell disappears. Such fossils are sometimes called steinkerns, a German term meaning “stone kernel.”

Nothing of the original shell may remain, yet its shape survives. The body is gone. The absence has become the fossil. 

Compression and Carbon Films

McAbee Fossil Plants

Plants and soft-bodied organisms may be buried and flattened beneath accumulating sediment. Pressure drives away liquids and gases, sometimes leaving a thin film rich in carbon.

These fossils can appear as dark, delicate outlines on the rock. Leaves may preserve their veins. 

Fish may retain the shapes of scales and fins. Soft-bodied animals can sometimes be recorded in astonishing detail.

They are the geological equivalent of silhouettes—life pressed into stone. Some of the lovely specimens we find at the Eocene McAbee Fossil Beds near Cache Creek, British Columbia, are a great example.

Amber Preservation

Amber begins as sticky resin produced by ancient trees. Small organisms such as insects, spiders, mites and fragments of plants can become trapped in the resin. As the resin is buried and chemically altered over time, it becomes amber.

Amber can preserve extraordinary detail: hairs, wings, compound eyes and delicate structures that would normally decay rapidly.

It can even preserve tiny moments of behaviour. Organisms have been found trapped while feeding, mating, carrying pollen or interacting with parasites.

Amber is not a perfect time capsule, however, and it has not provided usable dinosaur DNA. The mosquitoes of Jurassic Park remain unemployed. If you are looking for some superb examples of amber preservation, check out the collection of Harry Tabiner in the UK. He has a remarkable eye and enviable collection, which he shares online.

Ice, Dryness and Natural Tar 

Cold, arid or oxygen-poor conditions can dramatically slow decay. Mammoths preserved in frozen ground may retain hair, skin, muscle and stomach contents. Natural tar deposits can preserve vast collections of bones, although the remains themselves may be stained, altered or compressed.

These forms of preservation remind us that a fossil does not need to resemble a traditional stone skeleton. Fossilization is not a single recipe. It is a vast collection of unlikely outcomes.

WHAT ABOUT FOOTPRINTS? HOW CAN A HOLE BECOME A FOSSIL?

A footprint fossil begins with a perfectly ordinary step.

An animal walks across a surface soft enough to receive an impression but firm enough to retain its shape. Mud and damp sand are excellent candidates.

The track must then be buried before wind, waves, rain, other animals or enthusiastic members of the herd destroy it. A new layer of sediment settles over the surface, filling and protecting the impression.

With continued burial, both layers may harden into rock. Millions of years later, erosion separates them again. One surface may preserve the original footprint as a depression. The layer that filled the print may preserve a raised natural cast.

Tracks are not simply stamps of the foot. The animal’s weight can deform layers beneath the surface, producing structures known as undertracks. These may be less anatomically precise than the original print but can still record the passage of the animal.

Interpreting tracks requires caution. Wetness, sediment texture, erosion and the animal’s movement can all alter a footprint’s appearance. The same animal could leave surprisingly different tracks after walking only a short distance.

We must study the track, the sediment and the entire trackway—not merely find three vaguely pointed marks and immediately summon the media.

HOW OLD DOES SOMETHING HAVE TO BE BEFORE IT BECOMES A FOSSIL?

You may have heard that a fossil must be at least 10,000 years old.

That figure is commonly used as a practical dividing line in educational materials and some regulatory contexts, but nature has not installed an official fossil clock that rings at midnight on an organism’s ten-thousandth birthday.

We may use terms such as subfossil for relatively recent remains that are not fully fossilized or that retain considerable original material. The terminology can vary depending on the field, material and legal jurisdiction.

Age alone is not the only consideration. Geological context, preservation and scientific usage all matter.

An ammonite shell 100 million years old is unquestionably a fossil. A mammoth tusk 30,000 years old is also a fossil, even if some of its original material remains. Very recent bones from an archaeological site may be described as remains rather than fossils.

The boundary is useful, but it is not a magical transformation.

ARE ALL FOSSILS VISIBLE?

Not remotely. Some of the most important fossils on Earth are microscopic.

Microfossils include fossilized pollen, spores, algae, bacteria, protists and the tiny shells or skeletal elements of marine organisms.

They may be smaller than a grain of sand, yet they occur in enormous numbers and can be tremendously useful. Because some microscopic organisms evolved rapidly and lived across wide geographic areas, their fossils can help scientists date and correlate rock layers.

Microfossils also reveal ancient environments. Different species lived under different conditions, so their presence can provide clues about water depth, temperature, salinity, oxygen levels and climate.

Oil and gas exploration has long relied on micropalaeontology to interpret underground rock layers. A microscopic fossil no larger than a speck of dust may help identify the age and environment of rocks buried kilometres beneath the surface.

Dinosaurs receive the posters. Microfossils quietly organize geological time. Alas, always the bridesmaid, never the bride... Dinos get all the love.

CAN MOLECULES BE FOSSILS?

Ancient life can sometimes leave chemical evidence even when no recognizable body or trace remains.

These signals are often called chemical fossils or biomarkers.

Certain molecules are associated with particular groups of organisms or biological processes. Modified versions of those compounds may survive in ancient rocks, providing evidence that particular kinds of life were present.

Stable isotope patterns can also carry biological information. Living organisms use elements in ways that can leave characteristic chemical signatures in their tissues or surrounding sediments.

Chemical fossils require careful interpretation because geological heat, pressure and contamination can alter molecular evidence. But when combined with other data, they can help scientists investigate some of the earliest chapters in the history of life.

Sometimes life leaves a bone. Sometimes it leaves a footprint. Sometimes it leaves little more than chemistry.

IS A DINOSAUR SKELETON IN A MUSEUM MADE OF REAL FOSSILS?

Sometimes entirely. Sometimes partly. Sometimes hardly at all.

Complete dinosaur skeletons are rare. Museum mounts are often composites, combining fossil bones from more than one individual of the same species. Missing elements may be reconstructed as casts.

In some displays, the original fossils are too heavy, fragile or scientifically valuable to suspend in a dramatic pose. Museums may mount lightweight replicas while keeping the genuine fossils safely stored for research.

This does not make the display fake. A high-quality cast reproduces the shape and surface detail of the original fossil while protecting irreplaceable material. Casts can also be shared with museums, schools and researchers around the world.

Labels generally explain which elements are original fossils and which are reconstructed. It is always worth looking.

The glamorous skeleton towering over the gallery may be a carefully assembled ambassador for a far more fragmentary animal.

IS EVERY OLD BONE A FOSSIL?

No. Sometimes an old bone is just that, an old bone. Not a fossil. Age and appearance alone do not prove that something is fossilized. Modern bones can become stained by soil and minerals, making them look ancient. Conversely, genuine fossils do not always appear dramatically different from ordinary bone.

Identification may involve examining:

• Geological context
• Colour and density
• Surface texture
• Internal structure
• Mineral composition
• Associated fossils
• Degree of mineralization
• Evidence of recent organic material

And no, licking it is not the preferred scientific method but, I confess, it is helpful in the field. Not fully diagnostic, but helpful. I have a good friend Skippy who swears by it.

There is an old field trick based on the idea that porous fossil bone may stick slightly to the tongue, but modern bone can do the same, as can many ordinary rocks. The technique is unhygienic, unreliable and particularly regrettable when the mystery specimen is not bone at all.

Use a hand lens. Use comparative anatomy. Use laboratory analysis. Leave your tongue out of the peer-reviewed methodology.

WHY ARE FOSSILS SO RARE?

To become a fossil, an organism must pass through a series of improbable filters. Fossils are not rare per se, as I can think of localities with hundreds spread across the surface and more beneath, but they are rare in the sense that only a small percentage of the organisms that have lived have been preserved this way. To become a fossil is a bit of a process, as you might expect. 

First, the organism, dino, plant, or what have you, must die in a place where preservation is possible.

Then its remains must escape scavengers, decay, trampling, weather and destruction. They must be buried. The sediment must remain intact as it becomes rock. The fossil must survive heat, pressure, chemical alteration, faulting, erosion and the slow recycling of Earth’s crust.

Finally, it must become exposed—or be reached by excavation—at precisely the right time for someone to recognize it. Too early, and it remains buried. Too late, and erosion destroys it.

The fossil record is therefore both magnificent and profoundly incomplete.

Most organisms that ever lived left no known fossil. Entire species may have appeared, flourished and vanished without preserving a trace that we have yet discovered.

Soft-bodied organisms are especially underrepresented. Environments such as mountains, forests and tropical soils generally offer fewer opportunities for long-term preservation than lakes, river floodplains and marine sediments.

When we reconstruct ancient ecosystems, we are working with survivors of a second kind—not organisms that survived extinction, but evidence that survived geology.

IS A FOSSIL THE SAME THING AS A ROCK?

A fossil is preserved within a geological material, and many fossils have been heavily mineralized, but “fossil” and “rock” are not interchangeable terms.

A rock forms through geological processes and may contain fossils. A fossil is evidence of past life preserved within rock, sediment, amber, ice or another natural context.

The distinction can become wonderfully complicated.

A fossil shell may retain original shell material. A petrified log may be almost entirely mineral. A mould contains none of the organism but preserves its shape. A trace fossil may consist entirely of disturbed sediment.

So, is a fossil a rock? Sometimes it has effectively become one. But what makes it a fossil is not simply its material. It is the biological information it carries.

WHAT CAN ONE FOSSIL TELL US?

Far more than its name. A fossil’s anatomy may reveal how an organism moved, fed or defended itself. Growth rings can record seasons or age. Microscopic wear on teeth may reveal diet. Bone injuries can preserve evidence of accidents, disease, combat and healing.

The surrounding sediment can tell us whether the organism lived in a river, desert, forest, lake or sea. Associated fossils help reconstruct the plants, animals and microorganisms sharing that environment.

Chemical analysis may reveal temperature, water conditions, migration or food-web relationships. Footprints may preserve speed and direction. Burrows can reveal oxygen levels in ancient sediments. Coprolites can contain the remains of a final meal.

Even the way a body was buried matters. Were the bones scattered by a river? Gnawed by scavengers? Transported by waves? Buried in a sudden flood?

The study of what happens to an organism between death, burial and discovery is called taphonomy. It helps palaeontologists separate evidence of how an animal lived from evidence of what happened after it died. A fossil is not simply an object. It is a scene containing clues.

WHAT IS NOT A FOSSIL?

Not every interesting pattern in rock was created by life.

Mineral crystals, concretions, sedimentary structures and weathered rocks can resemble eggs, shells, bones, skin, feathers or entire mysterious creatures. These geological look-alikes are sometimes called pseudofossils. Or, leaverits, as in leave it right there. 

Manganese minerals can grow in branching patterns resembling ferns. Concretions can look remarkably like eggs. Layered rocks may split into shapes suggesting shells or leaves. Some rocks possess suspiciously skull-like features and an unreasonable amount of charisma.

The human brain excels at recognizing familiar forms. This tendency, called pareidolia, helps us see faces in clouds, animals in tree bark and dinosaurs in the landscaping gravel.

None of this makes an unusual rock uninteresting. A pseudofossil can still be geologically beautiful.

It simply tells a different story.

THE FOSSIL RECORD IS BIASED

The fossil record is sometimes imagined as a great stone library containing the complete history of life.

It is more like a library after fire, flood, renovation, several lost catalogues and four billion years of questionable management.

Some chapters are richly detailed. Others contain a few scattered sentences. Entire volumes are missing.

Organisms with shells, bones or teeth are more likely to be preserved than soft-bodied organisms. Aquatic environments are generally better represented than upland habitats. Abundant and widespread species have a greater chance of discovery than rare, geographically restricted ones.

Even human activity introduces bias. Fossils are more likely to be discovered where rocks are exposed, where researchers can travel and where scientific work has been funded.

Palaeontologists must account for these biases when interpreting patterns of diversity, evolution and extinction. An absence of fossils does not necessarily prove that an organism was absent. It may mean that the right rocks were not deposited, did not survive or have not yet been explored.

The fossil record is incomplete. But incomplete does not mean useless. It means we must read it carefully.

A FOSSIL IS A RELATIONSHIP

There is another way to think about fossils. A fossil is not merely a thing that was once alive. It is the relationship between life and the Earth that preserved it. The organism contributed its body or behaviour. The environment supplied mud, sand, ash, resin, ice or minerals. Time transformed the evidence. Erosion returned it to the light. Then someone noticed.

That final part matters. A fossil can lie exposed among a thousand ordinary stones and remain silent until a curious person stops, looks closely and asks a question.

What made this shape? Why is this shell inside a mountain? Who walked here? What kind of world once existed beneath my feet? Every fossil discovery begins with attention. And many great specimens have been found by folk of all ages (many of them too young to vote) who take notice of the world around them.

A MESSAGE THAT SURVIVED

To hold a fossil is to hold a contradiction. It is evidence of death that teaches us about life. It is a motionless object that may record movement. It is a fragment capable of revealing an ecosystem.

It is ancient, yet newly discovered.

The animal, plant or microorganism did not set out to leave us a message. The footprint was not made for our benefit. The shell did not settle onto the seafloor hoping to appear one day in a museum drawer.

And yet the evidence survived.

Across burial, mineralization, shifting continents, rising mountains and relentless erosion, something remained.

A tooth.

A leaf.

A burrow.

A trail across the mud.

A tiny, stubborn piece of deep time waiting for someone to recognize it.

That is a fossil.

MOVE OVER, T. REX: THERE IS A NEW KING IN TOWN

Eighty million years ago, long before Texas acquired highways, cattle ranches or the unshakeable belief that everything should be larger there, much of the region lay beneath a warm inland sea.

And cruising through those waters was an animal that appears to have taken the entire “bigger in Texas” philosophy rather seriously.

Meet Tylosaurus rex, a newly recognized species of giant mosasaur described in 2026.

It measured as much as 13.2 metres long, carried a mouthful of finely serrated teeth and possessed adaptations for unusually powerful jaw and neck muscles.

In short, it was an enormous marine lizard with steak knives for teeth and the disposition of something that had never once been asked to use its indoor voice.

The name Tylosaurus rex means “king of the tylosaurs.”

Yes, that makes it another T. rex. No, it was not a dinosaur.

Mosasaurs were enormous marine reptiles belonging to the squamate lineage that includes modern snakes and lizards. Their ancestors began as land-dwelling animals, but by the Late Cretaceous their descendants had become thoroughly committed to ocean life.

They developed streamlined bodies, paddle-like limbs and long, powerful tails. Some grew to extraordinary sizes and occupied the upper reaches of Cretaceous marine food webs.

While Tyrannosaurus rex would not appear until millions of years later, Tylosaurus rex was already patrolling the Western Interior Seaway—the vast body of water that once divided North America into eastern and western landmasses.

The resemblance between the two kings is largely one of reputation. Both were enormous apex predators, both possessed formidable skulls, and both appear to have occasionally settled disagreements by biting one another in the face.

Ah, royalty.

A FOSSIL HIDING IN PLAIN SIGHT

The story of Tylosaurus rex is a lovely little tale. It is one that sparks a gleeful, "oh, what do we have here?" The story begins inside a museum drawer.

Lead author Amelia Zietlow was studying a mosasaur fossil in the collection of the American Museum of Natural History when she noticed that it did not fit comfortably with Tylosaurus proriger, the species to which it had been assigned.

It was larger. Its anatomy was different. Its teeth carried fine serrations—an unusual feature among mosasaurs.

That suspicious specimen led researchers back through fossils held in several museum collections. More than a dozen specimens, most collected from northern Texas decades earlier, began to reveal a consistent pattern.

These were not simply especially large or slightly peculiar examples of T. proriger. They represented another species.

In May 2026, Zietlow, Michael Polcyn and Ronald Tykoski formally described Tylosaurus rex in the Bulletin of the American Museum of Natural History. The fossils came from rocks of Campanian age, approximately 80 million years old. Read the original scientific paper through the American Museum of Natural History.

This is one of my favourite kinds of palaeontological revelation: not a fossil newly pulled from the earth, but an animal newly seen.

The bones had been found. They had been collected, prepared, catalogued and cared for. What changed was the question being asked of them.

Museum collections are not mausoleums for finished ideas. They are scientific libraries, and occasionally one of the books turns out to have been shelved under the wrong name.

THE SIZE OF A SCHOOL BUS

The specimens assigned to Tylosaurus rex produced estimated body lengths ranging from about 7.7 to 13.2 metres. The largest was approximately the length of a school bus.

Imagine, if you will, a school bus with flippers, a long muscular tail and a skull designed to make the other residents of the seaway reconsider their afternoon plans.

The species was consistently larger than Tylosaurus proriger in the researchers’ comparisons, although the authors appropriately caution that preservation and sampling can influence apparent size differences in the fossil record.

The skull is where matters become especially interesting.

Tylosaurus rex possessed structural features associated with enlarged jaw and neck muscles. Its teeth were also finely serrated, providing cutting edges that would have helped it process large prey.

This was a long animal powerfully built at the business end.

The precise menu is not preserved as a tidy Cretaceous restaurant bill, but the Western Interior Seaway contained abundant fish, sharks, turtles, seabirds and other marine reptiles. A predator of this size and construction may have been capable of attacking a considerable variety of animals.

It was, in scientific terms, a very large problem with flippers.

THE BLACK KNIGHT (NO, NOT BATMAN... HE'S THE DARK KNIGHT...NON-AQUATIC)

One of the most memorable specimens is held by the Perot Museum of Nature and Science in Dallas.

Nicknamed the “Black Knight,” it is missing the tip of its snout and has a fractured lower jaw. Researchers believe the injuries were inflicted by another similarly sized tylosaur.

That means at least some members of this species survived spectacularly violent encounters with their own kind.

Whether these battles involved territory, mates, food or the Cretaceous equivalent of someone cutting ahead in the ammonite queue is impossible to know. Yet the injuries provide a rare glimpse into behaviour.

Bones do more than reveal anatomy. They can preserve the consequences of a life actually lived: disease, healing, predation, combat and survival.

The Black Knight was not simply a representative diagram of a species. It was an individual animal that experienced an exceptionally bad day and lived long enough for its damaged bones to record the event.

A FAMILY TREE IN NEED OF PRUNING

The 2026 study named a spectacular predator, and also revised the anatomical character list used to reconstruct relationships among mosasaurs. 

Some earlier analyses relied upon datasets assembled from limited specimens and repeated through successive studies. Returning to the fossils allowed the team to reassess which features were genuinely useful for distinguishing species and tracing evolutionary relationships.

Mosasaur evolution was remarkably rapid.

Their terrestrial ancestors entered aquatic environments during the Cretaceous, and within a relatively short geological interval, mosasaurs diversified into an impressive variety of marine predators. Some developed crushing teeth suited to hard-shelled prey. Others possessed slender jaws for catching fish. 

The tylosaurs became long-snouted, powerful hunters and were among the first mosasaur lineages to achieve truly gigantic body sizes.

Tylosaurus rex appears to represent an especially robust expression of that experiment: larger, heavily muscled and equipped with unusually sharp-edged teeth.

Evolution did not simply produce a big mosasaur. It produced a big mosasaur and then apparently gave it upgrades.

THE IMPORTANCE OF LOOKING AGAIN

There is something deeply satisfying about a fossil that refuses to remain what its label says it is.

For decades, these Texas specimens were known, preserved and studied under another name. Their discovery as a distinct species required someone to pause, notice the inconsistencies and ask whether the established identification was actually correct.

That is science at its finest.

Science is not weakened when an old interpretation changes. It is doing precisely what it is meant to do: responding to evidence, refining its explanations and occasionally admitting that the giant, serrated-toothed marine lizard in the cupboard has been misidentified.

The description of Tylosaurus rex also honours Texas palaeontologist John Thurmond, who had suspected decades earlier that the region’s unusual tylosaur fossils might represent a separate species. 

John had solid instincts. He was bang on.

LONG LIVE THE KING

Around 80 million years ago, Tylosaurus rex moved through a sea that no longer exists.

Above it flew pterosaurs and ancient birds. Beneath it swam fish, sharks, turtles and other marine reptiles. Ammonites drifted through the water carrying their beautifully coiled shells, presumably hoping not to draw attention to themselves.

Then the seaway vanished. Sediments became stone. Bones were buried, uncovered and placed in museums beneath names that seemed reasonable at the time.

It took a fresh pair of eyes to recognize the king.

Museum collections are a wonderful place to poke about and time and time again that looking with fresh eyes pays gold. It is true for Canada's first Sabre-toothed cat fossil and Vancouver Island's first dinosaur, too. They were both sitting pretty, woefully mislabeled then serendipity along with fresh eyes revealed the truth.

New species may already be resting in cabinets and storerooms, patiently waiting for someone to notice that their teeth are a little too serrated, their jaws a little too muscular and their identity altogether more magnificent than the label suggests.

And somewhere in Texas, the other T. rex is finally enjoying its coronation.

Lead Image: Amelia Zietlow, lead author of the new study, examines the Tylosaurus rex holotype skeleton (PMNS 8029) in February 2023 at the Perot Museum of Nature and Science.

Courtesy of Perot Museum of Nature and Science

Charming end note:

As well as these lovelies, there is also an ancient marsupial lion (Thylacoleo rex), a blind, cave-dwelling salamander (Typhlomolge rex), and a parasitic leech (Tyrannobdella rex), who are proudly in the T. rex club.

ROCK TO MUSEUM: JOURNEY OF A FOSSIL

Finding a fossil is like time-traveling with your hands. 

One moment you’re walking along a riverbank or quarry, scanning the ground, and the next—a fragment of bone, a whorl of an ammonite, or the outline of a fern leaf catches your eye. 

That thrill? It never gets old.

But the real magic happens after discovery. Fossils are often locked away in hard rock, fragile as porcelain and millions of years old. 

Paleontologists and citizen scientists use delicate tools—dental picks, air scribes, and fine brushes—to slowly free them, grain by grain. In some cases, a fossil is encased in plaster field jackets to keep it safe during transport, like a mummy wrapped for a journey through time.

Fossil Prep Lab

Once back in the lab, preparation becomes part science, part art. 

Stabilizing cracks, cleaning away stone, and sometimes even using microscopes to reveal the smallest details—all of this ensures the fossil tells its story clearly. 

For research, every surface and feature matters: teeth reveal diets, bone growth shows age, and even microscopic scratches whisper about ancient ecosystems.

When the work is done, fossils can either stay in collections for study or move into museum galleries. There, preparators mount them with custom armatures or create casts so the originals remain protected. Under lights and glass, these specimens connect us to their history—turning silent stone into storytellers. 

Prepping with an Air Scribe

Sometimes we see the specimen in isolation and other times we see who that creature was living amongst, how it made a living and what the environmental conditions were like. 

We might look at the pollen in the rock next to the fossil or bits of debris that help share these clues. 

Every fossil in a museum has taken this long journey: discovered in the field, carefully freed in the lab, then shared with the world. 

As you walk through the paleo exhibits at museums, you will begin to see the amount of time and patience that goes into preparing those specimens, both for study and display. 

A MOST PERSONAL FOSSIL: WHAT ANCIENT POO TELLS US ABOUT PREHISTORIC LIFE

Coprolites: Fossil Poop

Not every fossil enters the scientific record wrapped in dignity.

Some emerge from the rock with elegant ribs, formidable teeth or shells spiralled like mathematical poetry. Others are, quite unmistakably, ancient poo.

These geological indiscretions are known as coprolites—fossilized droppings left behind by animals that lived thousands or even millions of years ago. They may lack the grandeur of a dinosaur skull, but they are among the most intimate messages ever delivered from the prehistoric world.

A bone tells us that an animal lived. A coprolite tells us what it had for lunch. Sometimes, it also tells us whether lunch fought back.

The word coprolite comes from the Greek words kopros, meaning dung, and lithos, meaning stone. The term was introduced in the nineteenth century by the English geologist and fossil hunter William Buckland, a man who was famously fascinated by the less glamorous evidence left behind by ancient animals.

Despite the name, coprolites are not simply old droppings that have dried out and somehow survived. Like other fossils, their original material has usually been altered or replaced by minerals over time. Under the right conditions, an animal’s waste may be buried rapidly in sediment, protected from scavengers and decay, and gradually transformed into stone.

The result is a remarkably personal time capsule.

Inside a coprolite, we may discover fragments of bone, fish scales, shells, plant fibres, pollen, seeds and other traces of an ancient meal. Some even preserve the remains of parasites—proof that intestinal freeloaders have been making themselves unwelcome for a very long time.

Nature, it seems, invented digestive inconvenience well before humanity invented antacids.

WHO LEFT IT?

Determining that something is fossilized dung is only the beginning. Identifying the creature responsible can be considerably more difficult.

Unlike a tooth or skull, a coprolite rarely comes with the name of its producer conveniently attached. Its size, shape and contents can offer clues, but several animals living in the same environment may have produced similar droppings.

Researchers therefore study where the specimen was found, which animals are known from the surrounding rocks and what the coprolite contains. Spiralled coprolites, for example, may have been produced by animals with spiral-shaped intestinal valves, including certain ancient fishes and sharks. Large coprolites packed with shattered bone could point toward a sizeable carnivore with powerful jaws and an enthusiastic approach to dinner.

Even then, assigning a coprolite to a particular species may remain uncertain. Fossil poo is informative, but it is not always cooperative.

THE ORIGINAL DINNER RECEIPT

Coprolites provide evidence that skeletons alone cannot.

A collection of sharp teeth may suggest that an animal was a predator, but a coprolite containing chewed bone offers direct evidence of what at least one animal actually consumed. Plant-filled specimens can reveal the vegetation available in an ancient ecosystem. Fish scales, shell fragments and tiny bones may expose relationships between predator and prey.

Occasionally, tooth marks or partially digested remains reveal how food was processed. The condition of the material may even provide clues about digestive chemistry and how efficiently an animal broke down its meals.

Coprolites can also help reconstruct entire food webs. By combining their contents with fossil plants, pollen, footprints, bones and environmental evidence preserved in the surrounding rock, scientists can begin to understand who lived in an ecosystem, who ate whom and what happened after everyone had finished eating.

It is prehistoric ecology reconstructed from the least glamorous evidence imaginable.

THE PROBLEM WITH PREHISTORIC POO

Of course, not every suspiciously shaped lump is a coprolite.

Rocks are perfectly capable of impersonating biological objects. Mineral concretions, mud structures and strangely weathered stones may all resemble fossilized droppings—sometimes with alarming conviction.

Shape alone is rarely enough to confirm an identification. Researchers may examine a suspected coprolite under a microscope, study thin sections, analyze its chemical composition or use imaging technology to look inside without destroying it.

Phosphates associated with digested material can support an identification, as can recognizable food remains embedded within the specimen. Context matters enormously. A poo-shaped stone found in sediment containing abundant animal fossils is more promising than an identical lump discovered somewhere with no evidence of ancient life.

Sometimes a strangely shaped rock is a trace of prehistoric behaviour.

Sometimes it is simply a rock with an unfortunate silhouette.

Coprolites inevitably inspire laughter—and rightly so. Palaeontology does not become less serious when we admit that some fossils are funny.

But beneath the humour lies an extraordinary scientific resource. Coprolites preserve moments that bones often cannot: an animal feeding, digesting and moving through its environment. They capture behaviour rather than merely anatomy.

They remind us that prehistoric animals were not static museum displays. They hunted, grazed, scavenged, swallowed, digested, hosted parasites and occasionally consumed things they may later have regretted.

Millions of years later, we examine the mineralized remains of those meals and try to reconstruct the vanished worlds around them.

It is humbling, really.

We spend our lives hoping to leave behind something meaningful—a great work, a lasting legacy, perhaps a beautifully preserved skeleton in a respectable museum.

Have you found fossilized poop? Good on you! It is a mark of pride in any civilized collection!

Yet for some ancient creatures, the most revealing thing they ever left us was what they left behind.

Image: Asset id: 2461279721; Fossilized dinosaur feces (coprolites) on display at Rainbow Forest Museum and Visitor Center in Petrified Forest National Park, Arizona. Dinosaur droppings or poop fossil.