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After the Dinosaurs: Life in the Eocene

The Recovery

A depiction of the Eocene flora and fauna found in North America.

A depiction of the Eocene flora and fauna found in North America.

Our World- 49 Million Years Ago

Its 15 million years since the mass extinction that marked the end of the Age of Dinosaurs. All evidence of the environmental havoc left by this event has been erased from the Earth’s surface. This is the Eocene or ‘dawn of new times.’ The Earth is now a forest planet, a lush green paradise covered in tropical and sub-tropical jungle. Sea levels and global temperatures are high, you could swim in the Arctic Sea and magnolias thrive in Alaska. The spread of flowering plants that started in the dinosaurs’ era has continued and the forests are now full of fruit, flowers and scents. Among the larger vertebrates the influence of the dinosaurs lives on. The mammals have not been quick to occupy the new niches and no large predators have evolved to replace the giant reptiles. Instead, crocodiles hunt along the waterways and huge predatory birds comb the forests for prey. But mammals are better prepared for the future; while they have remained small, they have begun to diversify. In the forests, there are the first primates, rodents, hoofed plant eaters, carnivores and bats.

The Feathered Terror

Gastornis, or Diatryma was the largest predator on the Earth in the aftermath of the dinosaur extinction.

Gastornis, or Diatryma was the largest predator on the Earth in the aftermath of the dinosaur extinction.

Gastornis

A huge, heavily built, flightless bird, one of the largest animals around at the time and a fierce ambush predator.

Evidence: Only the imprint of a single thigh bone of Gastornis has been found in the Messel shales, near Frankfurt, but they are also common at the nearby site of Geiseltal and in the USA.

Size: 6 feet tall.

Diet: Meat, either hunted or scavenged.

Time: 56-41 million years ago.

Gastornis On Film

The Quiet Time

The Eocene jungle is very still just before sunrise. Around a dark lake the forest stacks up in dense green layers washed with an opaque pre-dawn light. A few bats flap silently between the upper branches, making their way back to their roosts. The hum from insects seems muted and the occasional haunting screech from a primate in the canopy only emphasises the silence. Suddenly ripples spread across the surface of the lake and waves appear from nowhere. There is a low rumble, which sends birds squawking from the trees and mammals scuttling from the undergrowth. A series of huge bubbles erupts from the lake, producing a small, sickly white cloud of gas. Beneath it the water stains red. Then it’s over, a short earthquake that leaves the denizens of the forest jumpy but unharmed.

Tremors are common here because the lake sits on a large island in the middle of the western Tethys Sea. To the north lies the giant Eurasian continent and to the south, Africa is slowly drifting northwards, squeezing the Tethys in between and causing volcanic activity across the area. The lake itself is the reason for the bubbles and gas. This is the dark secret. It’s about 1.2 miles across and more than 650 feet deep in places. At the very bottom is a dense layer of cold water trapped under a thick layer of warmer water. The cold water is stagnant and full of dissolved carbon dioxide. Every so often gas levels build up to such an extent that, when a tremor mixes the two layers, it can trigger the release of clouds of suffocating carbon dioxide which drifts towards the shore. This all makes the lake a very dangerous neighbour.

On this morning the cloud released is small, but its effects are deadly. A bat swoops low over the water, plucking a caddis fly out of the air, but as it turns it heads into the cloud of gas. After a few metres its delicate wings crumple and it drops with a small plop into the water. As the cloud reaches the reed and lily beds on the eastern shore it is already beginning to disperse. A palaeotis bird sitting on her nest opens her beak in a silent scream as she is suddenly robbed of oxygen. She shakes her head vigorously and staggers to her feet. Before the cloud can finish the job, it’s carried on into the fern and palm stands beyond on the morning breeze. The palaeotis puffs her dark brown plumage and settles back on her nest a little confused.

The cloud finally disperses as the ground rises. Here, where the under storey thins beneath huge laurel trees, the leaf litter has been scraped into a huge mound and topped with sticks and branches. Sitting on top of this, making a strange throaty whistle as she sleeps, is a gastornis. She is the largest bird on Earth, a carnivorous giant about 6 foot 6 tall, with a stout, muscular body. She cannot fly, but instead ambushes her prey amongst the dense undergrowth. In the dim light the shape of her huge body is hard to make out under her speckled black feathers, but there is no mistaking her livid red feathers and pale beak. The beak, in particular, is an awesome sight, a thick hatchet shaped weapon that can snap the backbone of a small horse in one bite. She is the queen of the jungle.

The gastornis was undisturbed by the tremor and oblivious to the gas cloud. She is a day time hunter and slumbers through the night, stirring only at dawn. All around her in the forest other diurnal creatures sleep on, unaware of the close brush some have had with death.

Modern, Yet Primitive

Leptictidium probably bore a striking resemblance to modern elephant shrews

Leptictidium probably bore a striking resemblance to modern elephant shrews

Leptictidium

These strange, hopping animals were part of a group that survived the great extinction at the end of the Cretaceous, but became extinct as the great tropical forests opened up at the beginning of the Oligocene. Three species are well preserved in the Messel shales, with outlines of fur and stomach contents.

Evidence: The leptictids were a widespread group and were around for a long time. Leptictidium itself was a specialised hopper with the best preserved specimens found in the Messel shales.

Size: Up to 3 feet long.

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Diet: Small lizards, small mammals and invertebrates.

Time: 50-40 million years ago.



Leptictidium On Film

A Dawn Start

Sunrise and, because of rain in the night, the forest begins to steam. High in the canopy a thick mist hangs between the trees, tinged orange by the dawn light. Lower down, the branches and leaves splinter the light into rays that pierce through the dark forest floor. A little distance from the lake a huge strangler fig stands lashed to the ground by its web of branches. Deep inside, the laurel tree it originally grew on has long since been killed. This makes a perfect shelter for a mother leptictidium and her two babies. Her nest, raised well off the ground, is dry and the entrance protected by an impossible maze of fig roots. Inside, the family are preparing for their morning hunt. Leptictidium are creatures of habit and the day always starts with a frantic washing session. The mother’s long pink nose twitches as she works methodically over her soft brown fur. As she shifts to an inspection of her long hopping feet her youngsters play with her naked tail. After one of them nips it, she stops grooming and scrambles out into the moist morning air. The youngsters follow obediently. Leptictidium are common in this forest and several different species can be seen bounding through the undergrowth after insects and lizards. This mother belongs to the largest species, measuring almost a metre from nose to tail. She pauses for a moment to sniff for danger and then bounces off through the fig roots. On a branch an owl puffs up its long ribbon like plumage and watches them go.

All leptictidium have a hunting trail that they follow through the undergrowth. Every morning and evening they work their way round the trail, catching food and clearing any obstacle that falls across their path. Should a predator ambush them, these trails become their escape routes. Today they will be used well. The three little mammals move swiftly through the steamy forest floor bouncing on their long back legs. The trail takes them down towards the lake and on to a small silt beach. The mother stops for a moment, then snaps at a large stag beetle on a log. She holds the wriggling insect firmly in her hands, while her sharp teeth make shirt work of it. The youngsters gather round to taste the food from her lips. It’s just two weeks since they were born and they are already being weaned. They must learn quickly how to hunt for themselves.

Their progress slows as they near the lake, with the mother finding more insects on which to feed. The trail also takes them along the top of the beach and, in this more exposed environment, the mother stops frequently to check for danger. There is a quiet in the air and her nose and whiskers quiver nervously.

It turns out that her caution is justified. A brief flash of red in a nearby tea bush is followed by the snap of a branch and the female gastornis bursts from her hiding place. In three strides she is on her prey, snatching at them with resounding cracks of her huge beak. But the leptictidium started moving the moment the mother saw the flash of red and, bounding at full pelt, they just about escape the lethal beak. With astonishing speed they head back up their trail through the fig roots and into the safety of their nest. The gastornis is left standing and, after a couple more strides, she loses interest in the hunt. She is too big to be a pursuit predator here; she relies more on ambush amid the dense forest.

The gastornis turns and struts down to the lake shore. With a low mist swirling round her clawed feet, her black speckled plumage and her menacing red stained face, her distinguished relationship to a very famous group of extinct animals is clear. She is the last representative of the carnivorous theropod dinosaurs, giant bipedal killers that once stalked the land. But in this new age she is a creature out of time. There are many other predators around, such as walking crocodiles and small but powerful creodont mammals. The gastornis is the biggest of all of them, but in contrast to the time of the dinosaurs there are no giant herbivores for her to feast on. She has to work hard for her living.

The First Horse

A fossil cast of propalaeotherium from the Messel site in Germany.

A fossil cast of propalaeotherium from the Messel site in Germany.

Propalaeotherium

These little forest animals are among the earliest horses known. They belong to the perissodactyls, a group which also includes tapirs and rhinoceros. Living in thick forest, they had four little hooves on their front feet and three on the back, and walked on pads, rather like dogs or cats.

Evidence: More than 35 beautifully preserved specimens of the two species are known from the Messel shales, and they have also been found at the nearby site of Geiseltal.

Size: Two species, one 12-14 inches at the shoulder, the other 22-24 inches.

Diet: Browsed on leaves and also ate fallen fruits.

Time: 49-43 million years ago.

The Walking Whale

This is the ancestor all living whales and dolphins. Its name, Ambulocetus literally means 'walking whale' and its easy to see why it was given the name.

This is the ancestor all living whales and dolphins. Its name, Ambulocetus literally means 'walking whale' and its easy to see why it was given the name.

Ambulocetus

Although Ambulocetus looked rather like a huge otter. It was in fact one of the earliest whales. It was less agile in the water than an otter, it seems to have been adapted for ambushing large prey, which it then drowned.

Evidence: One fairly complete specimen and several partial skeletons have been found in Pakistan.

Size: 10 feet long.

Diet: Carnivorous

Time: 59-50 million years ago.

How Whales Evolved

Whale Evolution In Action

End Of The First Shift

By mid morning the mist is long gone and the combination of high sun and dense greenery makes the air stiflingly humid. The forest here is typical of the tropical jungle that swathes most of this warm planet. The flowering plants that only started their evolution towards the end of the time of the dinosaurs are now dominant. Although a few ferns and cypresses hold on, the canopy is full of laurel, walnut, beech palm and dogwood. Climbers such as grapevines, honeysuckles and moonseeds wrap round these trees, while below magnolias, mulberries, tea and citrus bushes fight for light.

The variety on display is bewildering, but the things that would really confuse a time travelling dinosaur are the colours and the smells. The jungle is full of flowers and fruits, and in the morning heat their scent is overpowering. The green and brown dinosaur world of ferns and conifer needles has gone for ever. This seismic change in the flora is reflected in the type of animals that thrive here. The canopy is abuzz with wasps and bees. Among the branches and on the ground small mammals and birds grow fat on a diet of large fruit and soft flowers; gone is most of the rough, resin filled fare on which dinosaur plant eaters had to survive. This is a new Eden, a colourful scented world full of small animals, completely different from the age of the dinosaurs.

Under the canopy the darkness is broken by patches of magnesium white light, where the sun breaks through to the forest floor. A timid propalaeotherium horse tugs at a moonseed illuminated by one such ray of light. He is keen to draw it into the shadows where his dark dappled back will provide the security of camouflage.

A scuffle at the edge of the clearing sends the propalaeotherium scampering off. The leptictidium mother arrives and stops to wrestle with a lizard she has caught. The two youngsters catch up and join in. Suddenly the lizard’s brightly coloured tail pops off and starts to thrash about among the leaves. The youngsters leap back, pause and then pursue the tail with a series of hunting moves they have seen their mother perform. She meanwhile, holds tightly on to the lizard’s body and, after a firm bite to the back of the neck, it goes limp. She then heads off again for the nest. The youngsters follow, abandoning the tail to flick around by itself.

It is the end of the leptictidiums’ morning hunt and the family disappear under the strangler fig for their midday sleep. Inside the nest the mother finishes eating the lizard, although the youngsters will learn to hunt from her, she will never kill prey for them. They continue to try to suckle, but she is rapidly losing patience. Their time within her nest is running out, they will soon have to learn to be independent. For now, however, they all curl up and go to sleep.

Down by the lake, swifts dart across the surface, striking at the columns of mating insects. A python slips through the water lilies, heading for shore to digest a baby crocodile it has just caught. Nearby a much larger wake also heads for the shore. Just before it reaches the bank there is a splash and the top of a long brown head pops out of the water. At a glance it could be mistaken for a large crocodile, since there are plenty of those in the lake. But a closer look reveals that it is covered in a layer of fur and that there are whiskers bristling round its dark nose. Its eyes scan the bank and then, as it draws itself out on to the silt, it becomes clear that this extraordinary beast is nothing like a crocodile. Thick short hairs covers its entire body and large webbed feet make it move awkwardly on land. This is a male ambulocetus, part of a bizarre group of mammals that have evolved to take advantage of a similar niche to crocodiles, hunting animals along the water’s edge. Ambulocetus evolved on the Eurasian coast to the east of this forest and it is very rare to see one on the European islands. However, the jungle round the lake is full of bite sized prey, so it should not be short of food.

This male is about 10 feet long, not quite fully grown. He slides into position half in and half out of the water, in a patch of sedge that disguises his body. Then he settles down and waits. The ambulocetus’ hunting method requires a lot of patience. They have developed a special jaw and ear apparatus that is very sensitive to vibration. By resting their head on the ground they can sense the approach of prey and time their attack perfectly. Unfortunately, this does mean they have to wait for their victims to come to them.

In the oppressive heat of mid morning the ambulocetus starts his unique vigil. A huge flying ant lands on his forehead and explores the drying fur round his neck, but he does not move. After about half and hour a propalaeotherium appears from the undergrowth. She stands motionless in the shadows, her ears twitching. Then she nervously picks her way down to the lake to drink. Every few sips she looks around, alert to the slightest moves that would betray a predator. She is drinking just a few feet away from the stationary ambulocetus, but that is still too far for his purposes. Only when a large splash among the lilies sends the little horse jumping back does the predator make his move. With a flurry of dust and leaves, a huge fang filled mouth slashes sideways. But the horse was never near enough and, leaping high into the air, she disappears off into the jungle.

The ambulocetus decides to abandon his hunting, as the daytime temperatures are getting too high. He turns and slips into the water. After pushing off from the shore, a few sweeps of his webbed feet bring him to the deep, dark water that occupies most of the lake. Then his body and short tail into a series of slow, up and down undulations that propel him through the water without the use of his limbs. This movement is very distinctive of these new semi aquatic mammals and will one day be the trademark of their descendants, the whales. Below the ambulocetus, a crocodile moves pasts, its tail beating from side to side. The two do not bother each other.

The Modern Swarm

Army ants may not be as big as their Eocene ancestors but they're every bit as tenacious.

Army ants may not be as big as their Eocene ancestors but they're every bit as tenacious.

Giant Ants

Insects are a very ancient group, going back well before the dinosaurs, and during the Cretaceous Period, the first social ants evolved and started to make colonies. The Eocene giants, Formicium giganteum, are the largest ants ever found, and their colonies must have had a dramatic impact on the life of the forest. Their carnivorous habits may have made them the equivalent of modern driver or army ants, which are importabr predators in today's tropical forests.

Evidence: Fossils of Formicium giganteum have been found in the Messel shales and a very similar species in the nearby Eckfelf Maar.

Size: Workers 1 inch long, while the queens were only an inch longer, they possessed wingspans of over 5 inches.

Diet: Carnivorous, eating any animal that could not get out of their way.

Time: 49-44 million years ago.

Modern Killer Ants

The Swarming

In the direct sunlight the temperature continues to climb into the blistering 40s, but under the shade of the canopy it peaks in the lower 30s. In their strangler fig nest the leptictidium no longer lie bundled together; instead they are stretched out, breathing fast to keep cool. Beneath the laurel with its massive buttressed roots, the gastornis has returned to her nest. In the centre lies a single large blue green egg which she has been incubating for weeks. Today for the first time it’s making a noise. With her fearsome beak she gently turns it, revealing a small hole worked by the chick as it commences the monumental task of breaking out of its shell prison. The pointed end of a small yellow beak appears in the hole and then a round purple tongue accompanied by a sharp rasping call. The mother gastornis will not assist in this hatching, which could take the chick several hours; instead she checks round her nest for intruders and heads back into the forest to find fresh meat for her new arrival.

About 160 feet away from the nest and deeper into the forest, a propalaeotherium is enjoying a harvest of overripe graves. Although only 2 feet long, he stands on his hind legs and reaches up over 3 feet to gorge himself on the mouldy clusters hanging off the vine. His little hoofed paws are incapable of grasping anything, but he can easily pluck the fruit with his muzzle. Suddenly he drops and freezes, his ears rigid. Despite the blistering temperatures and the clear blue sky above, he can hear a sound like gentle rain. Slowly it gets louder and the horse bolts. Soon the forest floor has spiders and large insects, such as cockroaches and grasshoppers, scrambling after the larger animals.

Eventually the reason for the panic and the sound of rain becomes apparent. From around the laurel bough that supports the vine comes a column of giant ants. Soon the area where the propalaeotherium was standing is swarming with thousands of these ruthless hunters, tumbling over one another in a dark red tide as they search for fresh meat. They vary in size, with the largest being over an inch long, but en masse they can bring down surprisingly large prey. The sound of rain comes from the thousands of ants that have scaled the trees and bushes in the search for victims and, if not successful, simply dropped back down to rejoin their merciless colleagues. The swarm is the end of a long column that stretches 160 feet back to the buttress roots of an old walnut tree. Here a mass of ants form a temporary nest that protects their queen. Along the column countless hunters are bringing trophies back to the nest, including grubs, beetles, grasshopper legs, and even a bat’s wing.

All through the midday heat this devastating group predator works its way across the forest floor, methodically dismembering anything that cannot move out of the way. Soon the ants reach the gigantic strangler fig. The main column moves by, but individual outriders stay to explore the roots. Inside the strangler the leptictidium mother sleeps with her young, unaware of the danger outside. More and more ants forage amongst the roots. Despite the leptictidium’s size, if hundreds of giant ants fill the entrance to her nest she and her young will be lucky to survive.

After about ten minutes the number of ants around the fig decreases. In the column small bits of bloodied black feathers are being carried back to the nest. The swarm has discovered the gastornis nest 100 feet away. Ever since the ants arrived in the area this has been a danger. If they had come across the nest while the egg was still intact, the chick would probably have been left unharmed, but now the small window opened by the hatching chick has allowed the killers to pour in. Even if the mother had been present there would have been little she could do. By now the swarm has covered the huge nest and there is frantic activity around the egg itself. For the chick, it’s a slow and nightmarish death.