SLOTHS: THE RELATIVES WHO WENT TO SEA

We tend to picture sloths hanging quietly in a tree, looking as though their next appointment is sometime on Thursday.

Their fossil relatives had other plans. Some went into the ocean.

Meet Thalassocnus, a group of extinct sloths that lived along the Pacific coast of South America roughly nine to five million years ago. Fossils from Peru and Chile reveal animals that increasingly adapted to feeding in coastal waters.

A sloth grazing underwater may sound like a scheduling error, but its bones tell a convincing story.

Across successive species, researchers have documented thicker, denser bones. That extra weight would have helped counter buoyancy, allowing these animals to remain submerged while feeding. 

Changes in their skulls and limbs also support an increasingly aquatic lifestyle. Later species appear to have been better equipped to graze on submerged vegetation.

These were distant cousins of living sloths, rather than tree sloths that had simply fallen off a branch. Their evolutionary history records a remarkable shift from terrestrial life towards the sea.

And the modern family still has an unexpected aquatic talent. Living sloths can swim, using their long arms to move through the water. Those limbs may look wonderfully awkward on the ground, but water offers a different set of possibilities.

The fossil record gives us a much broader view of sloth life: animals that climbed, animals that walked on the ground, and animals that ventured beneath the waves.

Somewhere in that family history, a sloth looked at the ocean and found lunch.

Sources and Further Reading

• The Sloths that Once Swam in the Sea — Smithsonian Ocean.
• Little-Known Facts about Sloths — Smithsonian Institution.
• Valenzuela-Toro et al. (2025). Aquatic sloths (Thalassocnus) from the Miocene of Chile and the evolution of marine mammal herbivory in the Pacific Ocean.

WHY DID MEGALODON GO EXTINCT? AN OCEAN IN CHANGE

For millions of years, Otodus megalodon occupied a formidable place in marine food webs. Its broad, serrated teeth could slice through flesh and leave deep marks in whale bones. 

Yet even this mighty predator eventually disappeared.

Around 3.6 million years ago, the reliable fossil record of Megalodon comes to an end.

What happened to a shark so well equipped to feed on other large animals? 

The clues point towards several pressures acting together: changing prey communities, competition and the considerable demands of being an enormous predator.

Finding the Last Megalodon

Before we investigate why Megalodon vanished, we need to establish when.

In a study published in 2019, Robert Boessenecker and colleagues reviewed fossil occurrences, paying particular attention to well-dated marine rocks in California and Baja California. They found that supposedly younger records often involved uncertain collection information or older teeth that had been eroded from their original deposits and buried again.

A fossil tooth can therefore be older than the sediment surrounding it.

Their analysis supported an extinction around 3.6 million years ago, earlier than the roughly 2.6-million-year date used in some older accounts. This matters: events occurring a million years later cannot readily explain the shark’s disappearance.

A Changing Menu

In our earlier article, we met Piscobalaena nana, a small baleen whale whose bitten bones offer evidence of feeding by Megalodon. Encounters like these help us understand the resources available to this giant shark.

But marine mammal communities changed through time.

A 2016 study led by Catalina Pimiento found that Megalodon’s declining distribution coincided with changes in potential prey and the appearance of competing predators. Declining diversity among filter-feeding whales was one possible part of that story.

Fewer whale species does not automatically mean fewer individual whales. Nevertheless, changes in the kinds, sizes and distribution of prey could have altered where Megalodon could feed successfully.

For such a large predator, the availability of suitable meals would have mattered enormously.

Competition from Great Whites

One possible competitor was much smaller: Carcharodon carcharias, the great white shark.

In 2022, Jeremy McCormack and colleagues examined zinc isotopes preserved in shark teeth. These chemical signatures provide clues to an animal’s position in the food web.

Their results suggested that some early Pliocene great whites and Megalodons living in the same region fed at similar average trophic levels.

That finding supports possible overlap in their diets. It does not prove that they ate exactly the same species, or that great whites single-handedly drove Megalodon extinct. But competition for shared resources may have added pressure, particularly if suitable prey became harder to obtain.

We need not picture a battle between two sharks. Competition can unfold through thousands of ordinary feeding opportunities, with one animal securing a meal that another needs.

The Cost of Keeping Warm

Megalodon’s physiology adds another clue.

Research published in 2023 used chemical measurements from fossil teeth to investigate its body temperature. The findings supported the ability to maintain a temperature above the surrounding seawater.

This capacity, associated with regional endothermy, would have offered advantages to an active marine predator. But maintaining a large, relatively warm body also carries substantial energy costs.

The researchers proposed that these demands may have made Megalodon more vulnerable when environmental conditions and food availability changed.

A body that served a predator well in a productive ocean could become harder to sustain when dependable meals grew scarce.

Did Cooling Oceans Kill It?

Cooling is often presented as the straightforward answer to Megalodon’s extinction. The evidence is more complicated.

Pimiento and colleagues found no direct relationship between global temperature and the shark’s changing distribution in their analysis. Megalodon also inhabited a broad geographical range, making the idea of a strictly tropical shark unable to tolerate cooler water difficult to support.

Climate and oceanographic changes could still have mattered indirectly, by reshaping habitats and food webs. The distinction is between water becoming physiologically intolerable and an ecosystem becoming less able to support a giant predator.

When Size Became a Vulnerability

We have no single fossil that records the final cause of Megalodon’s extinction. Instead, researchers are assembling evidence from dated rocks, tooth chemistry, prey communities and the histories of other predators.

Together, these clues suggest a giant facing an increasingly difficult balance: finding enough food, meeting its energy needs and competing within a changing ocean.

Across this series, we have followed Megalodon through its teeth, its remarkable size, its meals and its early life. Its disappearance reminds us how closely even the most powerful predator depends on the wider community around it.

Megalodon’s teeth endured. The ocean that supported their owner changed.

Explore the series: Megalodon: A Guide to the Giant Shark

References and Further Reading

• Boessenecker et al. (2019). The Early Pliocene extinction of the mega-toothed shark Otodus megalodon: a view from the eastern North Pacific.
• Pimiento et al. (2016). Geographical distribution patterns of Carcharocles megalodon over time reveal clues about extinction mechanisms.
• McCormack et al. (2022). Trophic position of Otodus megalodon and great white sharks through time revealed by zinc isotopes.
• Griffiths et al. (2023). Endothermic physiology of extinct megatooth sharks.

WOMBATS: SQUARE POO AND GIANT FOSSIL COUSINS

The wombat looks like a small bear who has decided to become a bulldozer. It digs, grazes and produces something few of us would expect from a mammal: cube-shaped poo.

Yes, cubes. Nature has apparently found a way to manufacture building blocks from grass.

Researchers investigating bare-nosed wombats discovered that the corners form inside the intestine. 

Differences in the stiffness of the intestinal walls, combined with muscular contractions, help shape the droppings before they emerge. The wombat does not have a square exit. That question has been checked.

Female wombats have another practical feature: a backwards-facing pouch. For an enthusiastic excavator, this likely helps keep soil out of the baby’s accommodation.

But the fossil family album is where things get wonderfully oversized.

WHEN THE RELATIVES WERE ENORMOUS

During Australia’s Pleistocene, Diprotodon optatum wandered through landscapes shared with giant kangaroos and marsupial predators. The largest known marsupial, it could weigh around 2.7 tonnes and approach four metres in length.

Often nicknamed a “giant wombat”, Diprotodon belonged to a separate, extinct family. Wombats are among its closest living relatives, but it was a cousin on another branch of the family tree—not an oversized ancestor that eventually shrank into today’s burrow-dweller.

There were genuine giant wombats, too. Phascolonus gigas belonged to the wombat family and had powerful limbs and enormous, strap-like incisors. Its skull had a distinctive dish-shaped top, which researchers have suggested may have supported a protective pad used during head-butting contests. Prehistoric disagreements may have been quite a spectacle.

Living wombats give us a small, sturdy connection to that lost diversity of Australian marsupials. Their fossil relatives remind us that familiar animals can belong to family trees with some surprisingly large branches.

Whether those ancient giants also produced cubes is a question we should leave open.

A family resemblance only tells us so much.

Sources and Further Reading

• Intestines of non-uniform stiffness mold the corners of wombat feces — Soft Matter (2021).
• Ten things you need to know about wombats — CSIRO.
• Diprotodon optatum — Australian Museum.
• Prehistoric Australia — Australian Museum.

BABY MEGALODON: GROWING UP IN AN ANCIENT SHARK NURSERY

Megalodon Adult vs Baby Size Comparison

Awe. Who doesn't love babies? They are the cutest little things, right? Well, mostly....

Perhaps not quite as cute if they could bite your arm clean off! A baby Megalodon would have been an impressive neighbour but not a welcome one if you were on the menu. They were pretty big right from birth and they just kept growing! 

Even the lower published estimates place a newborn at around two metres long—already longer than many adult humans are tall. 

A more recent reconstruction suggests some may have entered the world at more than three and a half metres.

For an animal destined to become one of the ocean’s mightiest predators, that was quite a beginning.

But how do we find a shark nursery millions of years after its waters have vanished? We follow the teeth.

Small Teeth, Big Clues

In Panama, the rocks of the Gatun Formation preserve traces of a shallow tropical sea from roughly 10 million years ago. Among its fossils are teeth belonging to Otodus megalodon.

When Catalina Pimiento and colleagues examined this material for a study published in 2010, they found an unusual pattern: many of the Megalodon teeth were small.

That alone would not establish a nursery. Tooth size varies within a shark’s mouth, so a small tooth need not belong to a small shark. The team compared the fossils with teeth from other localities and considered their positions in the jaw.

Their findings supported an assemblage dominated by young sharks. Together with the shallow, productive marine setting, the evidence pointed towards an ancient nursery ground.

A Place to Grow

Many living sharks spend their early lives in nursery habitats. These areas can offer plentiful food and some protection while the youngsters grow.

For Megalodon, a productive coastal sea could have provided similar advantages. We should picture young predators finding their own meals, rather than mothers tending a classroom of pups. The fossils do not show parental care.

Nor does a concentration of shed teeth tell us exactly how many sharks gathered there at once. Sharks replace teeth throughout their lives, and a fossil deposit can accumulate over a long period.

What we have is a pattern of habitat use, preserved tooth by tooth.

A broader study published in 2020 examined nine fossil assemblages and identified five potential nursery areas, suggesting that this behaviour may have occurred across different regions and times.

Just How Big Was a Baby?

Teeth are not our only clues. Fossil vertebrae can preserve growth bands that researchers use to investigate a shark’s development.

A 2021 study estimated that one Megalodon was about two metres long at birth. A 2025 reassessment, using a larger reconstruction of the same individual’s adult length, revised its estimated birth size to approximately 3.6–3.9 metres.

These are reconstructions based on limited material, rather than measurements of a fossil newborn. The difference shows how strongly our answers depend on the body proportions used in the calculation.

If we use the four-metre Piscobalaena nana from our previous article for comparison, the larger birth estimate puts a newborn Megalodon close to that little whale’s entire length.

Did Such a Large Baby Need a Nursery?

That question has prompted a lively scientific debate.

Research published in 2022 proposed that some assemblages of small Megalodon teeth might reflect smaller adults living in warmer waters, rather than concentrations of youngsters.

However, two studies published in 2026 strengthened the nursery interpretation. An analysis of Iberian fossils supported a local nursery at the Reverté quarries in northeastern Spain. A separate reassessment found no significant relationship between temperature and body size in the dataset it tested, while nursery designation explained substantially more of the variation.

The discussion continues, but we have good reason to take these ancient nursery grounds seriously.

Before the Giant

We often meet Megalodon through its largest teeth and most dramatic size estimates. Its early life offers another way into the story.

Before becoming an enormous marine predator, each shark had to find food, navigate its surroundings and grow. The smaller teeth help us explore those years—and the coastal habitats that may have supported them.

A giant tooth tells us about a giant shark. Sometimes, the smaller teeth tell us where its story began.

Explore the series: Megalodon: A Guide to the Giant Shark

References and Further Reading

• Pimiento et al. (2010). Ancient Nursery Area for the Extinct Giant Shark Megalodon from the Miocene of Panama.
• Herraiz et al. (2020). Use of nursery areas by the extinct megatooth shark Otodus megalodon.
• Shimada et al. (2021). Ontogenetic growth pattern of the extinct megatooth shark Otodus megalodon.
• Shimada et al. (2022). Revisiting body size trends and nursery areas of Otodus megalodon.
• Shimada et al. (2025). Reassessment of the possible size, form, weight, cruising speed, and growth parameters of Otodus megalodon.
• Herraiz et al. (2026). The Iberian fossil record of Otodus megalodon rejects Mediterranean dwarfism and supports nursery use.
• No evidence for Bergmann’s rule in Otodus megalodon (2026).

WHAT DID MEGALODON EAT? BITE MARKS, WHALES AND FOSSIL CLUES

Megalodon had the teeth to make a meal of a whale. Fossils show that it did—but the menu was more varied than a succession of enormous animals. They ate their fill of what was swimming in the ocean around them. 

Small whales, other marine mammals and perhaps other sharks all enter the story.

To investigate what Otodus megalodon ate, we can follow bite marks on bones and chemical signals preserved inside teeth. Some fossils even allow us to put a name to an animal that encountered those formidable jaws.

MEET PISCOBALAENA NANA

Piscobalaena nana was a small extinct baleen whale from Peru. In a 2017 study, Alberto Collareta and colleagues described marine mammal remains from the Pisco Formation bearing bite marks attributed to megalodon. Among them were remains identified as this particular whale.

For an animal we usually picture tackling giants, a smaller whale might seem an unambitious choice. Yet a large predator need not pursue the largest available prey. The researchers proposed that relatively small marine mammals were important food for adult megalodon along this ancient coast. [1]

There is one detail the fossils cannot settle: whether these animals were hunted or scavenged. Tooth marks record feeding, but the fragmentary bones do not reveal how the meal began.

DOLPHINS AND THE BITE NEAR THE TAIL

Fossils from Maryland and North Carolina provide another striking image: small toothed-whale vertebrae with deep gouges on opposing sides. Those gouges tell of a terrible end for those whales as they swam through our ancient seas. Researchers interpreted the marks as the result of bones being forced between adjacent megatooth-shark teeth. It is a rather horrifying thought.

These vertebrae came from the narrow region just ahead of the tail flukes. Biting there could disable a swimming animal, although scavenging could not be ruled out. The authors attributed the clearest examples to megalodon or its close relative Otodus chubutensis. The whales themselves were not identified to species. [2]

For a sense of their appearance, the paper illustrates the long-snouted dolphin Xiphiacetus bossi. It is a useful comparison, rather than the confirmed identity of the bitten animals.

OTHER ANIMALS IN THE NEIGHBOURHOOD

The Pisco ecosystem also included the small dolphin Brachydelphis mazeasi and the fish-eating beaked whale Messapicetus gregarius. Both offer good subjects for illustrations of the smaller cetaceans sharing these ancient seas. 

They are plausible prey candidates, but that is an ecological inference: the specimens discussed here do not demonstrate that megalodon ate either species. We do not have fossil bite marks on their fossil remains but it seems likely that they were lurking on that ancient lunch menu as they shared waters with these mighty predators. [3]

WHAT THE TEETH REVEAL

In 2022, nitrogen-isotope research placed sampled megalodon exceptionally high in ancient food webs, consistent with eating other predators. Zinc-isotope studies offer further evidence of feeding relationships.

A 2025 analysis of an early Miocene ecosystem suggested that megatooth sharks had considerable dietary flexibility, including variation between populations. Its material includes Otodus megalodon/chubutensis, so the conclusions concern these closely related sharks rather than megalodon alone. [4, 5]

These chemical signals tell us about feeding patterns. They do not identify the species in a particular meal.

A POSSIBLE BASKING-SHARK MEAL

A June 2026 study described basking-shark remains associated with giant megalodon vertebrae from Denmark. Fragments of gill rakers and tiny skin denticles led the authors to propose possible stomach contents.

If that interpretation is correct, another shark was on the menu. The fossil basking shark was not securely identified as today’s species, Cetorhinus maximus; a photograph of the living animal would illustrate the group, not the exact fossil prey. [6]

The most satisfying menu therefore comes with names where the evidence permits them, and questions where it does not. Piscobalaena nana gives us a particular whale. Gouged tail vertebrae bring us close to a feeding encounter. Tooth chemistry helps place those events within a much larger ocean food web.

Explore the series in Megalodon: A Guide to the Giant Shark, or examine the fossil teeth behind the bite marks.

RESEARCH AND FURTHER READING

1. Collareta and colleagues (2017): Megalodon feeding traces on marine mammals from Peru. DOI: 10.1016/j.palaeo.2017.01.001.
2. Godfrey and colleagues (2018): Megatooth-shark bite marks on toothed-whale tail vertebrae. Figures 1–3 show the fossils; Figure 4 illustrates Xiphiacetus bossi.
3. Collareta and colleagues (2021): The ancient Pisco marine ecosystem. Figure 9F–G shows a Piscobalaena nana skeleton with shark bite marks; these particular marks should not automatically be assigned to megalodon. DOI: 10.3390/jmse9111188.
4. Kast and colleagues (2022): Nitrogen isotopes and megatooth-shark trophic levels.
5. McCormack and colleagues (2025): Miocene food webs and dietary flexibility in megatooth sharks.
6. Shimada and colleagues (2026): Danish vertebrae and associated basking-shark remains. DOI: 10.26879/1674.

HOW BIG WAS MEGALODON? MEASURING A SHARK WE HAVE NEVER SEEN WHOLE

Massive Megalodon Shark

If you were sitting on the side of a 25-metre swimming pool and looked down to see a shark, this fellow would fill one end to the other. 

It is wild to consider that megalodon would leave just a wee bit of room at either end of the pool. He would fill it entirely! The image you see here on the left is a reconstruction that gives you the scale of these amazing animals.

At a proposed 24.3 metres, megalodon would make that a rather crowded pool. Fortunately, this is an exercise we can do from dry land.

The 24.3 estimate comes from a scientific reconstruction, not an animal measured from nose to tail. No complete skeleton of Otodus megalodon has been found. 

To estimate its size, researchers work with teeth, rare vertebrae and comparisons with other sharks. The difficult part is deciding how those surviving pieces fitted into the body of the living animal. [1, 2]

A TOOTH GIVES US A STARTING POINT

Megalodon Teeth Comparison

In our previous article on megalodon teeth, we looked at what their shape and preservation can reveal. Measuring the shark behind them requires another step: a relationship between the size of a tooth and the length of its owner.

Researchers have used great white sharks to develop those relationships. Apply an unsuitable equation to different teeth from one animal and the results can disagree dramatically.

A 2021 study by Victor Perez, Ronny Leder and Teddy Badaut tested an established crown-height method on teeth belonging to a single megalodon. It returned lengths ranging from 11.4 to 41.1 metres. The animal had not changed size between calculations; the method was producing inconsistent answers.

The team developed an approach using the combined crown widths of associated teeth. Applied to an exceptionally large isolated upper tooth, their method produced an estimated maximum of about 20 metres. [3]

THE BACKBONE COMPLICATES THE PICTURE

Teeth are not our only evidence. A specimen in Belgium preserves 141 associated vertebral centra: the central parts of the vertebrae. These offer a rare opportunity to investigate megalodon beyond its mouth.

In a 2024 reassessment, Phillip Sternes and colleagues highlighted a problem. An earlier estimate placed the entire shark at about 9.2 metres, yet the reconstructed length of its incomplete vertebral column was about 11.1 metres.

The preserved backbone could hardly be longer than the whole animal.

The discrepancy challenged the use of great white proportions as a guide. The authors argued for a more elongated body than the familiar bulky reconstruction. Without the missing head, tail and remaining vertebrae, however, its precise outline remains uncertain. [4]

WHERE THE 24.3-METRE ESTIMATE COMES FROM

In 2025, Kenshu Shimada and colleagues examined body proportions across 165 living and extinct shark species. They used comparisons within megalodon’s broader shark order to estimate the missing parts around the Belgian vertebral specimen. Their reconstruction placed that individual at approximately 16.4 metres.

They then scaled from it to larger vertebrae reported from Denmark, arriving at a possible length of about 24.3 metres for the larger animal. Their analysis also supported a relatively slender body.

This is why a longer megalodon does not simply mean stretching a great white photograph. The proportions are part of the question being investigated. The authors describe their conclusions as working hypotheses for further research. [1]

A MISSING SPECIMEN RETURNS

The Danish fossils have a story of their own. Excavated at Gram in 1978, the vertebrae were damaged during a later move and thought lost. Their rediscovery allowed researchers to examine surviving material directly.

A June 2026 study confirmed a reported vertebral diameter of 23 centimetres. An important measurement behind the size estimate could now be checked against the specimen itself.

The paper also explored growth, producing a theoretical attainable length of 28 metres. That figure needs particular care: the growth model is highly tentative, and it does not document a shark that actually reached that length. The authors recommend retaining 24.3 metres as their most reasonable estimated maximum, pending better skeletal evidence. [2]

HOW BIG WAS AN ORDINARY MEGALODON?

A proposed maximum does not describe every member of a species. A particularly large fossil attracts attention precisely because it may represent an exceptional individual. The Danish animal is interpreted as a rare size outlier, rather than a template for every adult megalodon. [2]

We should also ask what a number refers to. Is it an estimate for one fossil individual, a proposed maximum for the species or a theoretical growth limit? Those answers cannot be exchanged without changing the meaning.

Nor are estimates from different methods the two ends of a single measured range. The 20-metre and 24.3-metre figures come from different evidence and assumptions. Putting them side by side is useful; treating the space between them as a settled answer would hide the research behind them.

MEASURING THE UNCERTAINTY

For now, the answer is that megalodon was enormous, with recent vertebral research proposing an exceptional maximum of approximately 24.3 metres. We should keep “estimated” beside that number. A decimal place can make a reconstruction look more exact than its underlying evidence allows. [1, 2]

When we see a life-sized model or an illustration, we can ask which fossils informed it, which proportions were borrowed from living animals and where the reconstruction fills gaps. Those questions make the image more interesting. We begin to see the decisions behind the animal’s outline.

So return to the swimming pool for a moment. The comparison gives us room to appreciate the scale. The fossils tell us why we are still discussing exactly how much room this shark would need.

Next in the series: What Did Megalodon Eat? Bite Marks, Whales and Fossil Clues.

Explore the collection in Megalodon: A Guide to the Giant Shark.

RESEARCH AND FURTHER READING

1. Shimada, K. and colleagues (2025). Reassessment of megalodon’s possible size, form and biology. Palaeontologia Electronica, 28(1):a12. DOI: 10.26879/1502.
2. Shimada, K., Elstrup, M., Lauridsen, H., Sørensen, T. and Siversson, M. (2026). Rediscovery of gigantic megalodon vertebrae from Denmark. Palaeontologia Electronica, 29(2):a27. DOI: 10.26879/1674.
3. Perez, V. J., Leder, R. M. and Badaut, T. (2021). Body length estimation from associated fossil dentitions. Palaeontologia Electronica, 24(1):a09. DOI: 10.26879/1140.
4. Sternes, P. C. and colleagues (2024). White shark comparison reveals a slender body for megalodon. Palaeontologia Electronica, 27(1):a2. DOI: 10.26879/1325.

MEGALODON'S BITE: WHAT ITS GIANT TEETH CAN TELL US

Megalodon teeth

A megalodon tooth is a wonderful thing to hold in your hand. The broad crown, thick root and finely serrated edges give us a sense of the animal behind it, even when the rest of that animal is missing. 

Some of the largest teeth approach 18 centimetres in length. That is a substantial piece of dental equipment, especially when we consider that whales were among the animals on the menu.

But size is only the beginning. Look closely at a tooth and we can begin to separate several stories: how it functioned in a living shark, where it sat in the mouth and what happened after it settled into the sediment.

ROOT, CROWN AND CUTTING EDGE

The pointed blade is the crown. Beneath it, the heavy root anchored the tooth in the mouth. Fine serrations run along the crown’s cutting edges, although these may be worn or missing in a fossil specimen.

On the inward-facing surface, near the junction of crown and root, a band called the bourlette provides another useful feature to examine. 

A broad triangular crown, fine serrations, a substantial root and this band help specialists recognise a typical megalodon tooth. Identification depends on the combination of features, along with comparisons and geological context. A large triangular tooth alone is not enough.

Shark teeth are made of dentine with a hard outer covering called enameloid. These mineralised tissues preserve much more readily than the cartilage forming most of a shark’s skeleton. We therefore have an abundance of teeth to study, while complete megalodon skeletons remain unknown.

A SHARK THAT KEPT REPLACING ITS TEETH

Sharks produce replacement teeth throughout their lives. As teeth are lost, others move forward to take their place. Megalodon shed thousands over a lifetime, leaving many opportunities for teeth to be buried and preserved.

This changes how we read a find. A loose fossil tooth does not necessarily mark the place where a shark died. Its owner may have lost it while feeding or during normal tooth replacement, then carried on swimming. The tooth began a rather different journey, into the sediment and eventually the fossil record.

SMALL POINTS, LONG HISTORY

The familiar megalodon blade developed within a lineage of megatooth sharks whose teeth changed through time. Some earlier forms carried small side points, called lateral cusplets, beside the main crown.

In a study of 359 fossil teeth from Maryland’s Calvert Cliffs, researchers traced a gradual decline in those cusplets through millions of years. The broad, serrated cutting tooth we associate with adult megalodon emerged through a lengthy transition.

Juvenile megalodon could also have cusplets, which complicates identification. Their presence does not automatically place a tooth in an earlier species. We need to consider variation within an animal’s life as well as changes across an evolutionary lineage.

The broad blade and serrations are consistent with cutting flesh. They help us understand how the teeth worked, but a loose tooth cannot identify its owner’s last meal. For that, we turn to other evidence, including bite marks on fossil bones and chemical clues preserved in tooth tissues.

WHY ARE FOSSIL SHARK TEETH DARK?

Fossil teeth often catch our attention because of their colour. Browns, greys and blacks reflect burial conditions and minerals in the surrounding sediment, rather than the colour of the living shark’s smile.

The root and crown can respond differently during fossilisation, so one tooth may preserve contrasting colours. Fossilisation does not require every part of the original tooth to be replaced by new minerals, either. Some of its original mineralised tissue can remain.

Colour belongs to the history of preservation. On its own, it cannot establish a precise age or confirm the species.

WHEN A SCHOOL LESSON CHALLENGED THE MEASUREMENTS

One of the most appealing megalodon research stories began with a classroom exercise. Palaeontologist Victor Perez and teacher Megan Higbee Hendrickson used replicas of teeth from one megalodon to help students calculate the shark’s length. Depending on which tooth they measured, the answers varied wildly.

The students’ arithmetic was not the problem. The exercise exposed limitations in the equations being used.

Teeth vary in size and shape around a shark’s mouth, so their original positions matter when we use them to estimate body length. Perez and colleagues went on to investigate a method based on tooth width. Their work offers a useful reminder that a fossil measurement and an estimate of a whole animal are different things. The estimate depends on a model, and that model needs testing.

A small tooth does not automatically mean a baby shark, either. It could come from a smaller individual, occupy a different position in the jaw or be missing part of its original structure. Context makes the measurement useful.

TAKE A CLOSER LOOK

Choose a clear tooth photograph, ideally showing both faces and a metric scale. Find the root and crown, then examine the edges. Are the serrations intact? Is the tip complete? Can we see the bourlette? What differs between the two faces?

Make a note of what is visible before deciding how it happened. A broken tip is an observation; an encounter with a particular prey animal is a proposed explanation that needs more evidence.

That distinction is useful well beyond shark teeth. It allows us to enjoy a fossil for what it preserves while recognising how much remains to be learned. With megalodon, one tooth can bring us close enough to study the cutting edge of an animal whose full outline is still a matter of research.

We will explore that missing outline in our next instalment, How Big Was Megalodon? Measuring a Shark We’ve Never Seen Whole.

Explore the growing collection in Megalodon: A Guide to the Giant Shark, or begin with Is Megalodon Still Alive? 10 Big Questions About the Biggest Shark.

FURTHER READING

• Florida Museum of Natural History: Fossil Shark Teeth and Are shark teeth fossils true fossils?.
• Smithsonian National Museum of Natural History: Megalodon specimen and dental tissues. The catalogue retains an older scientific name.
• Perez and colleagues (2017): Late Miocene chondrichthyans from Lago Bayano, Panama.
• University of Florida (2019): Research on the evolution of megatooth shark teeth.
• Florida Museum (2021): The classroom exercise and megalodon size estimates; Perez, Leder and Badaut (2021): Estimating lamniform body size from teeth.
• Natural History Museum, London: What can shark teeth tell us?.

Lead Image: Megalodon Teeth: Image Asset ID: 2099621176

TRILOBITE EYES: THE ORIGINAL STONE-COLD STARE

The ancient oceans were full of watchful eyes. Some bulged. Some perched on stalks. And some belonged to animals that looked at the world through crystal lenses.

Meet the trilobites.

Armoured, joint-legged and occasionally extravagantly spiny, these marine arthropods had a remarkable approach to eyewear. Many built their eye lenses from calcite.

Yes, a mineral.

Long before anyone peered through a magnifying glass at a fossil, that fossil’s original owner was doing a little mineral-assisted looking of its own.

CRYSTAL CLEAR, AT LEAST IN PRINCIPLE

Calcite is a form of calcium carbonate, familiar to geologists as a common mineral in sedimentary rocks. In trilobites, it also became part of an optical system.

Transparent calcite could transmit and bend light. The arrangement and structure of the lenses helped make that material useful for vision.

Aspidonia shildtiere by Ernst Haeckel, 1904

These were biological structures grown by a living animal. The lenses did not simply become mineralised millions of years after death.

That distinction is rather delicious: part of the reason we can study these ancient eyes is that their owners built durable lenses while they were still using them.

Imagine leaving behind your spectacles for palaeontologists to examine hundreds of millions of years later.

Quite the extended warranty.

ONE EYE, MANY LITTLE WINDOWS

Most sighted trilobites had compound eyes, with numerous lenses arranged across a curved surface. The general idea will be familiar if you have ever admired—or attempted to discourage—a fly.

Each lens faced a slightly different direction. Together, the visual units helped the animal gather information about its surroundings.

Different trilobites invested in very different arrangements. Some had relatively modest eyes. Others sported large, bulging visual surfaces.

There was no single standard trilobite view of the world. An animal moving over the seabed faced different visual challenges from one swimming above it.

Where is the food? What moved beside me? Is that shadow something with an appetite?

Practical questions. Particularly the last one.

EYES ON STALKS: A BOLD FASHION CHOICE

Then there is Asaphus kowalewskii, an Ordovician trilobite whose eyes rose above its head on long stalks.

It looks as though someone fitted a small armoured animal with a pair of periscopes.

Raised eyes could have helped a trilobite look above the immediate surface around its body. The familiar picture of this animal watching from a partly buried position is an interpretation of its anatomy, rather than a behaviour we have directly witnessed.

Still, those stalks invite a splendid mental image: a quiet seabed, a little movement in the sediment, and two eyes maintaining a deeply suspicious watch.

Prehistoric neighbourhood surveillance.

THE TECHNICAL BIT WITH THE EXCELLENT NAME

Many trilobites had closely packed lenses in eyes called holochroal eyes.

Certain trilobites, including Phacops, had another arrangement known as schizochroal eyes. Their larger, more distinctly separated lenses have attracted particular scientific interest because of their complex construction.

You do not need to memorise the terminology to appreciate the important part: trilobite eyes were varied, specialised structures.

Researchers examine their shapes, materials and internal details to investigate how they worked. Occasionally, exceptional preservation reveals structures beneath the lenses, bringing us closer to understanding the living visual system.

Exactly what the world looked like to a trilobite remains a harder question.

A fossil can preserve a lens. It cannot hand us a recording of an Ordovician afternoon.

SOME SKIPPED EYES ALTOGETHER

For all this optical extravagance, some trilobites had no eyes.

Sight offers fewer advantages where useful light is scarce. Blind forms may have inhabited dark water or lived in ways that made other senses more valuable.

Evolution accommodates both towering eyes and no eyes at all, depending on the circumstances.

The ancient ocean had room for several approaches to getting through the day.

A LITTLE FACE-TO-FACE TIME

Next time you see a well-preserved trilobite, give its head a closer look.

Those small raised surfaces may preserve individual lenses: tiny remnants of an animal’s connection with its surroundings.

Once, light passed through them while a living creature searched, moved and responded to the sea around it.

Now we lean over the rock and look back.

Hundreds of millions of years between us, and still an opportunity for a little eye contact.

Which would you choose for your own ancient-ocean adventure: crystal compound eyes, periscope stalks, or the confidence to navigate without either?

OREODONTS: MOUNTAIN TEETH & ANCIENT OREGON

Cast of Oreodont, John Day Formation

With a pig-like body, a sheep-ish silhouette and a distant connection to camels, an oreodont is a lovely reminder that ancient life did not always fit neatly into familiar categories. 

These curious mammals were enormously successful, leaving abundant fossils in places as far apart as South Dakota’s Badlands and Oregon’s John Day country. 

The specimen you see here is a cast of an oreodont fossil from the John Day Formation—a chance to meet one of the characters that browsed ancient Oregon long before its present landscape took shape.

Oreodonts lived in North America from roughly 40 million to 5 million years ago, spanning much of the Eocene through the Miocene. They belonged to the artiodactyls, the even-toed mammals whose living members include camels, bison and bighorn sheep. 

Oreodont Reconstruction

Many oreodonts had four hooved toes and sturdy, short-legged bodies. Camels are generally considered their closest living relatives, though the relationship is a distant one. No family reunion invitations have been forthcoming.

Their teeth reveal a plant-eating lifestyle, with cheek teeth suited to processing vegetation such as leaves and shoots. Some oreodonts may have gathered in herds, offering a little collective protection against predators, including the formidable cat-like nimravids. 

Being a herbivore required a balance between finding something delicious and avoiding becoming something delicious yourself.

What’s in a name? What’s in a tooth?

Despite the tempting association, oreodonts have nothing to do with chocolate biscuits dunked in milk. Their name combines the Greek roots for “mountain” and “tooth”, referring to the peaks and ridges of their molars. Think miniature mountain ranges tucked into a mouth. The tooth connection appears in familiar words such as dentist and orthodontist, though I suspect an oreodont orthodontist would have needed a particularly sturdy chair.

Teeth are among palaeontology’s most useful clues. Their size, proportions and arrangement of cusps and ridges can help distinguish one animal from another, sometimes down to species. Yet a single tooth does not always provide a tidy answer. A recent study of John Day oreodonts excluded certain isolated teeth from its analyses because they were too easily confused between groups. A good identification depends on knowing both what a feature reveals and where its limits lie.

There are intriguing clues elsewhere in the skull, too. Some oreodonts, including Leptauchenia, possessed greatly enlarged auditory bullae—the bony capsules enclosing the middle-ear cavities. These structures have been studied for what they might reveal about hearing and habitat. Enlarged middle-ear cavities can improve sensitivity to lower-frequency sounds in living mammals, but they do not, by themselves, tell us the size of an extinct animal’s external ears. Fossils invite us to listen carefully, even when their owners have been silent for millions of years.

The browsers of John Day

In Oregon, the John Day Formation preserves an extraordinary sequence of changing environments. Its middle and upper portions contain major fossil assemblages dating from approximately 30–18 million years ago. Volcanic ash, stream deposits and ancient soils accumulated across landscapes that became cooler and drier over time. The beautiful blue-green claystones of the Turtle Cove Member owe their colour to celadonite, a mineral formed during alteration of the volcanic ash. A lovely palette for a remarkably rich fossil archive.

Eporeodon occidentalis

One of the region’s familiar oreodonts is Eporeodon occidentalis, a stocky browser with four hooved toes and prominent canine teeth. Its imposing tusks accompanied a set of cheek teeth built for processing plants. 

Across the Turtle Cove landscape, oreodonts shared wooded and more open habitats with three-toed horses, mouse-deer and an assortment of predators. These communities changed through the millions of years preserved in the rock; they were never one enormous prehistoric gathering frozen in time.

Then there was Agriochoerus, a wonderfully unusual oreodont relative with curved claws instead of hooves. Its limb anatomy suggests that it could climb, perhaps using trees in a way comparable to living tree kangaroos. That interpretation gives us a delightful possibility: a sheep-sized browser taking its leafy dining arrangements upstairs. With nimravids in the neighbourhood, the option may have had considerable appeal.

Fresh research is still refining this story. A September 2026 study by Meaghan M. Emery-Wetherell, Nicholas A. Famoso and Joshua X. Samuels documented a major change around the Picture Gorge ignimbrite, a volcanic rock layer that helps researchers correlate the fossil-bearing beds. Agriochoerus disappeared locally, the large terrestrial Promerycochoerus arrived, and Eporeodon persisted but became smaller. 

Oreodont Diversity in the Kimberly Member

Regional oreodont diversity peaked in the Kimberly Member, roughly 26.6–25.5 million years ago, with as many as five species represented during that interval.

Each of the fellows you see on the left bear a familial resemblance to their peers but with slight differences.

That is what makes an oreodont fossil—or a carefully made cast—such a compelling introduction to deep time. 

Follow those mountain teeth into the surrounding rocks and an entire world begins to emerge: leaves overhead, ash settling through the air, and unfamiliar animals going about the wonderfully ordinary business of staying alive.

Lead Image: Cast of an oreodont fossil from the John Day Formation, Oregon. Oreodonts were extinct plant-eating mammals whose distinctive cheek teeth inspired their name, “mountain teeth”. This lovely was cast by Rod Bartlett, Vancouver Paleontological Society, back in the mid 2000s.

BEFORE THE FIRST FOSSILS: THE MISSING CHAPTER OF ANIMAL LIFE

Mongolian Base Camp

Somewhere in the immense stretch of time before familiar shells, claws and skeletons, our earliest animal ancestors began their evolutionary adventures. Finding out when they appeared is another matter entirely.

How do you find the beginning of a story when its opening pages may never have been preserved?

A study published in Science Advances on 2 October 2026 brings that question into sharp focus. Led by Orin M. Lole Durbin and colleagues, the research suggests that animal origins could extend back roughly 800–700 million years—considerably earlier than their widely accepted body fossil record. 

Crucially, this is an estimate from evolutionary analyses, rather than the discovery of an 800-million-year-old animal. The distinction matters. Deep time already has enough mysteries without us accidentally issuing a birth certificate.

Consider what a fossil actually tells us. A recognisable animal preserved in dated rock establishes that its kind existed by that time. It does not necessarily reveal when the lineage first evolved. Your oldest surviving family photograph works much the same way: it records someone’s presence on a particular occasion, without marking the beginning of the family.

An empty photograph is trickier. Was nobody there, or was the camera pointing elsewhere?

For palaeontologists, that is a serious question.

In China, the approximately 590-million-year-old Weng’an Biota preserves microscopic organisms with remarkable detail, yet contains no definitive animals. Its apparent silence has been used to help limit how far back animal origins could extend. The reasoning depends on an assumption: animals living then would have been preserved and recognised in those deposits.

Enter Mongolia, carrying a rather awkward piece of evidence.

Mongolia's Lake Khövsgöl

The researchers investigated microfossils from the Kheseen Biota, an assemblage dated broadly to about 550–526 million years ago. 

The Kheseen Biota comes from northern Mongolia, where rocks of the Kheseen Formation crop out in a discontinuous belt stretching roughly 250 kilometres along the western side of Lake Khövsgöl. 

These rocks record a world very different from the lake landscape we see today: an ancient marine basin where carbonate sediments, mud and phosphate-rich deposits accumulated. 

Within those phosphatic rocks, microscopic organisms were preserved in extraordinary detail, leaving a tiny window into an ocean that vanished more than half a billion years ago. It is a wonderfully humbling contrast—a vast geological landscape holding some of its most revealing secrets at a scale smaller than a grain of sand.

Its preservation and microscopic inhabitants resemble those of Weng’an. It, too, lacks definitive animals.

But here is the delicious complication: animals unquestionably existed somewhere in the world during that younger interval. Their absence from Kheseen cannot mean that the entire animal kingdom had yet to evolve.

It is rather like inspecting a beautifully preserved guest list from a gathering of botanists and concluding that nobody on Earth was a dentist.

The record may be excellent. The sample may still be selective.

Kheseen’s missing animals could reflect the environments represented, the conditions of preservation, or a combination of factors. Whatever the explanation, the comparison weakens the argument that Weng’an’s missing animals provide a dependable limit on animal origins.

This is where living animals enter our fossil detective story.

Researchers can compare genetic differences among species and use evolutionary models, anchored by fossil evidence, to estimate when their ancestral lineages separated. This approach is called a molecular clock.

Think of it as a clock that requires careful setting. Fossils supply reference points; assumptions about the oldest plausible ages also influence the answer.

The team tested older geological constraints in these analyses. Their results supported an origin for animals approximately 800–700 million years ago, demonstrating how strongly the estimated timing depends on the maximum ages supplied to the models.

That possibility takes us towards an extraordinary chapter of Earth history. The interval overlaps the approach to, and beginning of, the Cryogenian Period, associated with the immense glaciations popularly called Snowball Earth. Animal beginnings might therefore belong to a world entering some exceptionally dramatic climatic upheavals.

Imagine the challenge of finding such an ancient beginning. We are asking rocks to preserve something recognisable, survive geological upheaval, become exposed where someone can investigate them, and then yield a clue we know how to read.

A demanding filing system, geology.

The next step is to keep searching across different ancient environments and kinds of preservation, bringing body fossils, traces of activity and chemical evidence into the conversation. The precise age of animal origins remains unresolved.

For me, that uncertainty is part of the wonder.

Every fossil is a surviving fragment of a much larger world. Sometimes the most compelling discovery is realising how much of that world could still be missing.

The opening pages of our animal story may be out there.

We are learning where—and how—to look.

Image: Mongolia's Lake Khövsgöl by sayursaying.com

BLOOD, BONES & CREATURES OF THE DARK

A spooky adventure with the Fossil Huntress

Gather close, curious creatures. Tonight, we’re slipping into the shadows to meet animals whose lives are every bit as fascinating as their spooky reputations.

Our journey takes us from a vampire’s roost to the deep ocean, through the forests of Madagascar—and back into the fossil record.

Bring your curiosity. Perhaps leave your neck covered.

VAMPIRE BATS: DINNER WITH A BITE

Before Dracula donned his cape, evolution had already produced a flying mammal with a taste for blood.

Only three living bat species feed exclusively on blood. And their table manners deserve a little clarification: vampire bats make a small cut with sharp front teeth, then lap up the blood with their tongues. Think tiny midnight diner with very particular menu requirements.

But these little creatures have a surprisingly tender side. A successful feeder may share some of its meal with a hungry roostmate by regurgitating blood.

Yes, it sounds like a dreadful dinner invitation. For a hungry bat, it can be a lifesaving gift. Even vampires benefit from having good friends.

A VAMPIRE IN THE FOSSIL RECORD

Giant Vampire Bat, Desmodus draculae

Of course, this is the Fossil Huntress, so we must rummage through a few ancient bones.

Meet Desmodus draculae, an extinct giant vampire bat with a scientific name worthy of its own horror film. 

Larger than today’s common vampire bat, it inhabited parts of the Americas during the Pleistocene, with fossil finds stretching from Mexico to Argentina.

Picture an Ice Age landscape as daylight fades. Somewhere beyond the shelter of your fire, a vampire bat takes flight.  

Giant Vampire Bat, Desmodus draculae

Its fossil remains offer a tantalizing glimpse of an Ice Age world where vampire bats shared the landscape with giant ground sloths, armoured glyptodonts, heavy-bodied toxodonts, ancient horses and elephant relatives called gomphotheres.

Which of these ancient giants might have supplied a midnight meal? 

Horses seem plausible candidates, given that living vampire bats feed on them, while researchers have suggested that ground sloths—and even glyptodonts—may have offered accessible feeding sites around their feet. A glyptodont’s bony armour would have put much of its body off the menu, but softer, exposed areas could have left an opening for a determined diner.

Toxodonts and gomphotheres add to the intriguing possibilities, though we cannot confidently identify them as meals—or rule them out simply on the assumption of thick skin. The precise menu of Desmodus draculae remains a mystery.

Imagine a tiny winged visitor finding a vulnerable patch of skin on a sleeping Ice Age giant. The fossil record has excellent material for a Halloween story. It practically writes itself!

VAMPIRE SQUID: A CLOAK IN THE ABYSS

Vampyroteuthis infernalis

Now, down we go into the deep sea to meet Vampyroteuthis infernalis. Its scientific name translates to “vampire squid from hell.”

A rather dramatic introduction for an animal that eats drifting debris.

Despite its name, the vampire squid drinks no blood. It isn’t a true squid, either, but belongs to a separate branch of the cephalopod family tree. Its dark body and webbed arms give it a wonderfully cloak-like appearance.

Its dinner is “marine snow”: sinking organic material that includes the remains of tiny organisms and fecal particles. Yep, this fellow eats poop. Two slender feeding filaments help gather this falling feast from the surrounding water.

Vampire Squid drawn by Carl Chun, 1911

Imagine dressing like a gothic sea lord, receiving a name that promises eternal terror, and spending your evenings quietly collecting leftovers.

The image you see here on the left is a vampire squid (Vampyroteuthis infernalis) from the work of Carl Chun, a German marine biologist who led the pioneering Valdivia deep-sea expedition of 1898–1899. 

Chun formally described the species in 1903, and it was he who gave it a scientific name that translates to “vampire squid from hell”—quite the introduction for a little creature that spends its days gathering drifting ocean leftovers. 

His expedition helped reveal the extraordinary abundance and diversity of life hidden in the ocean’s dark depths. I am oftly fond of cephies of all kinds but this fellow holds a special place in my heart as a Halloween icon with a very practical approach to recycling.

THE AYE-AYE: SOMETHING TAPPING IN THE TREES

Aye-aye, Daubentonia madagascariensis

For our final encounter, we enter Madagascar’s nighttime forests.

There, an aye-aye (Daubentonia madagascariensis) moves through the branches. This nocturnal lemur has large ears and an extraordinary, slender middle finger—an appearance seemingly assembled for a moonlit ghost story.

Then comes the tapping.

Tap. Tap. Tap.

The aye-aye taps wood and listens for clues to hidden cavities where insect larvae may be waiting. Once it locates a promising spot, it gnaws through the wood and uses its specialized finger to extract a meal. That mysterious scratching in the darkness? Someone looking for a grub.

Its unusual appearance conceals an ancient family connection. Aye-ayes are primates, related to Madagascar’s ring-tailed lemurs, sifakas, indris and tiny mouse lemurs. Their lineage branched away early from that of all other living lemurs, leaving today’s aye-aye as the sole surviving species of its family, Daubentoniidae. More distant relatives include the lorises and galagos of Africa and Asia.

And there was once a larger relative tapping through Madagascar’s ancient landscapes.

The extinct giant aye-aye, Daubentonia robusta, is known from subfossil remains found in southern and southwestern Madagascar. These relatively recent ancient bones reveal an animal with remarkably robust limbs, estimated to have weighed roughly two-and-a-half to five times as much as its living cousin. Imagine meeting that larger silhouette on a moonlit branch.

For deeper roots, we must look beyond Madagascar. Researchers have proposed that Plesiopithecus, a primate from Egypt around 34 million years ago, and Propotto, known from younger Miocene deposits in Kenya, were ancient relatives of the aye-aye lineage. These are proposed evolutionary relatives, rather than fossils of the modern aye-aye itself, offering tantalizing clues to an African chapter in its family history.

The fossil trail remains patchy, with enormous gaps in Madagascar’s early primate record. But the clues we do have make that little tapping sound all the more remarkable: a living animal finding its supper with adaptations shaped by a long and extraordinary evolutionary history.

Tap. Tap. Tap.

A midnight snack, with deep roots. That mysterious scratching in the darkness?

Someone looking for a grub.

A LITTLE WONDER IN THE DARK

A bat that shares its blood supper. A deep-sea “vampire” gathering marine snow. A forest primate tapping for hidden treats. An extinct vampire waiting to be discovered in ancient sediments.

Nature gives us plenty to shiver about—and even more to wonder at.

This Halloween, spare a little admiration for the creatures behind the costumes. Their adaptations, appetites and ancient histories tell stories no haunted house could invent.

Which would you join for a midnight adventure: the vampire bat, the vampire squid or the aye-aye?

Happy Halloween from the Fossil Huntress. May your treats be plentiful and your fossil finds delightfully frightful.

Image: A Vampire Squid (Vampyroteuthis infernalis) drawn by Carl Chun, 1911. Chun formally described the species in 1903, giving it a scientific name that translates to “vampire squid from hell”—quite the introduction for a little creature that spends its days gathering drifting ocean leftovers. His expedition helped reveal the extraordinary abundance and diversity of life hidden in the ocean’s dark depths.

KUMIMANU: THE GIANT PENGUIN THAT TIPPED THE SCALES

Kumimanu adapted from Nobu Tamura

Some penguins belong on postcards. This one deserves its own weigh station.

Around 57 million years ago, an enormous penguin swam through the seas of what is now Aotearoa New Zealand. Known from fossils described in 2023 as Kumimanu fordycei, this ancient marine lovely had an estimated body mass of around 150 kilograms.

That is a great deal of penguin.

The researchers’ calculations placed it among the strongest contenders for the heaviest penguin ever discovered. Its fossils come from rocks dated to between 59.5 and 55.5 million years ago, during the late Palaeocene—a time when life was exploring new possibilities following the extinction of the non-avian dinosaurs.

A GIANT HIDING INSIDE A BOULDER

The story begins with fossil-bearing boulders on the coast of North Otago, on New Zealand’s South Island.

Palaeontologist Alan Tennyson of the Museum of New Zealand Te Papa Tongarewa collected the penguin fossils studied by the team in 2016 and 2017. Locked inside the rock were clues to an ancient community of seabirds, including one exceptionally large individual.

Researchers created three-dimensional digital models of the bones to help study their anatomy. Among the remains was a remarkable humerus—the upper wing bone—that offered a way to investigate the bird’s size.

For those of us who love fossils, there is something especially pleasing about this part of the story. A boulder on a beach can hold the remains of an animal that once breathed, hunted and moved through a world we will never see.

The rock keeps its secrets until patient eyes and careful preparation bring them into view.

HOW DO YOU WEIGH A FOSSIL PENGUIN?

There are practical difficulties with asking a bird that has been dead for millions of years to step onto a scale.

Instead, palaeontologists look for relationships between the dimensions of bones and body mass in living animals. Those relationships can then help them estimate the mass of extinct relatives.

For this giant penguin, calculations using the length and width of the humerus produced estimates of approximately 148 and 160 kilograms. These are estimates with uncertainty, rather than a precise reading of the animal’s weight. Even so, both point to an exceptionally hefty bird.

Its height is less certain. We do not have a complete skeleton, and a heavy penguin is not necessarily the tallest penguin.

For comparison, large emperor penguins—the biggest penguins alive today—can weigh around 45 kilograms. Our fossil heavyweight could have outweighed three of those substantial birds combined.

WINGS FOR WATER

Penguins descend from flying birds, but their ancestors gradually became specialists in moving through water.

Once flight was lost, staying light enough to become airborne was no longer a requirement. Larger bodies became possible, and there were potential advantages to growing big.

A bulky, warm-blooded animal loses heat more slowly relative to its volume than a smaller one. For a bird spending time submerged, retaining warmth could make a considerable difference. Researchers have suggested that this may have helped drive the early evolution of giant penguins.

Greater size also raises intriguing questions about diving and feeding. Could these birds reach food that smaller penguins could not? Their bones invite us to investigate, although we cannot yet reconstruct their daily lives in detail.

AN ANCIENT PENGUIN WITH A DIFFERENT FLIPPER

The specimen described as Kumimanu fordycei was discovered in 2017, encased in a hard concretion. Fossil preparator Al Mannering carefully freed its bones from the rock.

The remains include a humerus, a vertebra and portions of other wing, shoulder-region and leg bones. They are now held at Te Papa in Wellington.

Those wing bones reveal an animal with some ancestral features, including flipper bones that were less flattened than those of living penguins. This was an early member of the penguin evolutionary story, with a combination of features different from the birds we know today.

The name fordycei honours New Zealand palaeontologist R. Ewan Fordyce and his contributions to understanding ancient life.

A LITTLE SCIENTIFIC NAME DETECTIVE WORK

There is a further twist to our giant’s story.

In a 2025 study, Gerald Mayr and colleagues questioned whether Kumimanu fordycei should be recognised as a separate species from the previously named Kumimanu biceae. They argued that the differences in size and bone shape could fall within the variation expected within one species.

They therefore considered K. fordycei likely to be a junior synonym of K. biceae. In everyday language, that means the newer name may refer to the same species as the older name.

This is part of the fascination of palaeontology. Finding a fossil begins a conversation. Further specimens, comparisons and analyses can change how we interpret it.

Whether these remains represent a separate species or an especially large individual of an already named one, the bones still belonged to an extraordinary penguin.

A BEACH WORTH VISITING—FROM A SAFE DISTANCE IN TIME

I have a soft spot for fossils that overturn our everyday expectations.

We know penguins as charismatic seabirds: diving, calling, tending their young and bustling about on shore. Then the fossil record introduces a relative with enough heft to make us reconsider the whole picture.

Somewhere along an ancient New Zealand coast, a very large bird once emerged from the sea. Millions of years later, pieces of its skeleton emerged from stone.

A beach boulder, a patient preparator and a remarkable wing bone have given us a glimpse of that encounter.

And what a lovely great penguin it was.

WYOTEUTHIS: THE CHUNKY BELEMNITE FROM THE JURASSIC SEA

Wyoteuthis linsterorum, holotype

Some fossils make you pause because they are beautiful. Others catch your eye because something about them simply does not fit.

Two unusually stout fossils from Wyoming have done just that, revealing a newly named marine animal with a wonderfully distinctive shape—and an unexpected place in the history of ancient oceans.

Meet Wyoteuthis linsterorum, a squid-like cephalopod that lived around 160 million years ago. Its scientific description was published in September 2026, giving a name to a creature whose story had been waiting decades to unfold.

A belemnite with a little extra roundness

If you have collected belemnites, you may know their smooth, pointed guards: the solid internal structures that often survive after the softer parts of these marine animals have disappeared.

Wyoteuthis takes that familiar form in an unusual direction. Its guard is remarkably broad, reaching about six centimetres across. The researchers describe these as the thickest belemnite guards yet known.

Wyoteuthis linsterorum

That makes it a wonderfully chunky fossil, though a thick guard does not automatically tell us how large—or how round—the living animal was. Reconstructing its soft body remains a more uncertain undertaking.

An ancient family with a late-surviving branch

The surprise goes beyond its proportions.

The fossils belong to the Megateuthididae, a belemnite family that flourished earlier in the Jurassic but had largely disappeared before Wyoteuthis lived.

These specimens reveal a surviving branch of that family in the northeastern Pacific region. 

Their discovery adds a small but significant piece to our understanding of where ancient marine lineages persisted.

There is something deeply pleasing about that. A fossil can be both a physical object you hold in your hand and evidence that changes the shape of a much larger story.

Two finds, decades of curiosity

The first specimen was found in the late 1990s by Dr Burkhard Pohl. A second, discovered by fossil collector Cliff Linster, was donated to the Wyoming Dinosaur Center in 2019.

Together, they helped researchers recognise a new species. The name linsterorum honours Cliff and his family. Cliff died in June 2026, before the research was published.

The study brought together Alexey Ippolitov, Jessica Lippincott, William Wahl and Dean Lomax. Both fossils are reported on display at the Wyoming Dinosaur Center in Thermopolis.

For those of us who love looking closely at fossils, this is a lovely reminder to stay curious about the familiar. An odd shape deserves a second look. So does the specimen that refuses to fit neatly beside its neighbours.

Sometimes, a new chapter in the history of life begins with someone noticing that one fossil looks a little different.

Suggested image caption

The unusually stout guard of Wyoteuthis linsterorum, a newly described Jurassic belemnite from Wyoming. Image: Ippolitov, Lippincott, Wahl & Lomax (2026), Figure 5, Papers in Palaeontology. Source, CC BY.

Further reading

Ippolitov, A. P., Lippincott, J. L., Wahl, W. R. & Lomax, D. R. (2026). ‘The big chunky belemnite’: a new relict megateuthidid from the Oxfordian (Late Jurassic) of Wyoming, USA, and its place in the evolutionary history of the group. Papers in Palaeontology, 12, e70123.

Figure 5: Wyoteuthis linsterorum, holotype specimen. Image: Ippolitov, Lippincott, Wahl & Lomax (2026), Figure 5, Papers in Palaeontology. Source, CC BY. The holotype—the specimen used to name the species—with photographs and CT sections.

Figure 6: Wyoteuthis linsterorum gen. et sp. nov., paratype, WDC JSI-22.  The second specimen, showing its chunky shape and internal anatomy.

SINOSAUROPTERYX AND ARCHAEOPTERYX: FEATHERS, FOSSILS AND THE ORIGINS OF BIRDS

Sinosauropteryx and Archaeopteryx

A feather can change how we see an entire animal.

Preserved beside a delicate skeleton, its faint outline tells us something bones alone cannot: this ancient creature wore plumage. 

Two remarkable fossil animals, Sinosauropteryx and Archaeopteryx, have helped transform our understanding of dinosaurs and the origins of birds.

One was a small predator with a fuzzy coat and a striped tail. The other had feathered wings, sharp teeth and a long, bony tail. 

Together, they invite us to look beyond the familiar image of dinosaurs as entirely scaly giants—and look a little more closely at the birds outside our windows.

SINOSAUROPTERYX: A DINOSAUR IN A FUZZY COAT

Sinosauropteryx lived in what is now northeastern China approximately 125–122 million years ago, during the Early Cretaceous. About a metre long, much of that length taken up by its slender tail, this small theropod walked on two legs and hunted little animals. A fossil preserving a lizard in its stomach offers a wonderfully direct glimpse of dinner.

But the feature that made Sinosauropteryx famous lies around its skeleton.

A fringe of fine, filamentous structures traces parts of the body: the remains of a simple feather covering. These were unlike the broad, neatly vaned flight feathers of a raven or eagle. They would have given the animal a soft, fuzzy appearance.

First discovered in 1996, Sinosauropteryx became a landmark in the study of feathered dinosaurs. Here was evidence that plumage extended beyond early birds into other dinosaur branches.

That distinction matters. A feather covering does not automatically make an animal a flyer.

Research on the preserved colour patterns has also revealed alternating bands along the tail, a darker back, a lighter underside and a dark facial marking described as a “bandit mask.” These patterns suggest camouflage played a role in its life. Countershading—a darker upper surface above a paler belly—can reduce the visual effect of shadows, helping an animal blend into its surroundings.

Even through stone, we can begin to recover something of this little hunter’s appearance.

ARCHAEOPTERYX: AN ANCIENT WING IN LIMESTONE

Travel farther back, to approximately 150 million years ago, and we meet Archaeopteryx.

Its fossils come from the Late Jurassic limestones of southern Germany, particularly the celebrated Solnhofen region. These deposits preserve extraordinary details, including the impressions of feathers surrounding delicate bones.

Look at an Archaeopteryx fossil and the wings immediately catch your eye. Long feathers spread outward from the forelimbs, giving the animal an unmistakably birdlike outline.

Then look again.

There are teeth in the jaws, clawed fingers on the wings and a long tail supported by a series of vertebrae. This combination of features makes Archaeopteryx especially valuable for understanding the early evolution of birds.

Its name means “ancient wing”—a fitting name for an animal that has prompted generations of palaeontologists to ask how dinosaurs took to the air.

Could it fly? Research examining the internal geometry of its wing bones supports active, flapping flight. Its capabilities and wing stroke, however, differed from those of modern birds. The evidence points towards short flights rather than the sustained aerial journeys we see in many birds today.

FEATHERS BEFORE FLIGHT

There is a delightful wrinkle in this story: the fuzzy, flightless Sinosauropteryx lived millions of years after the winged Archaeopteryx.

They do not form a simple sequence in which one became the other. Evolution branches. Different dinosaur lineages lived with different combinations of feathers, skeletons and ways of moving.

The broader fossil record shows that feathers were present in dinosaurs that could not fly. Early plumage may have helped with insulation, display and other functions before feathers became part of the equipment for aerial travel. The flight feathers of birds belong within that longer evolutionary history.

Birds are living theropod dinosaurs. The chickadee investigating a branch, the gull turning above the shoreline and the raven watching you with considerable interest all belong to a dinosaur lineage that survives today.

FOLLOWING THE STORY IN OSLO

If your travels take you to Norway, the Natural History Museum in Oslo, or Naturhistorisk museum, offers an opportunity to explore this connection between dinosaurs and birds.

The museum has featured Sinosauropteryx and Archaeopteryx through reconstructed displays, bringing their feathered forms into three dimensions. Its exhibition material describes a downy Sinosauropteryx model, while reporting on its bird evolution displays documents a fully feathered Archaeopteryx reconstruction. These are representations of the ancient animals; visitors should check individual labels to distinguish models, casts and original fossils.

The museum’s current permanent exhibition, Evolution of Life, is housed in Brøggers hus. It follows life through geological time, exploring changing ecosystems and important evolutionary developments among animals and plants. Fossils provide the clues connecting these ancient worlds.

Located at Sars’ gate 1, 0562 Oslo, Norway, the museum grounds include the Botanical Garden. Beyond palaeontology, visitors can explore exhibitions on animals, minerals, geology and climate. Tøyen metro station is approximately a six-minute walk from the southern entrance in Monrads gate. Check the museum’s official website for current exhibitions, opening hours and admission information, particularly if you hope to see a specific display.

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