66 — 23 Ma

Paleogene

Mammals diversify rapidly to fill the void left by dinosaurs, and primates first appear.

Northern Hemisphere

Eocene Arctic swamp forest with Metasequoia redwoods

During the Early Eocene Climatic Optimum, about 53–50 million years ago, Ellesmere Island lay within a surprisingly warm, humid Arctic world. This scene shows a swampy floodplain forest dominated by dawn redwoods (Metasequoia) and swamp cypresses such as Glyptostrobus, their tall trunks rising from dark, tannin-stained channels and peaty ground under persistent mist and low polar sunlight. On the muddy bank rests a crocodilian comparable to Asiatosuchus, evidence that even the high Arctic supported frost-free wetlands and reptile life during one of the warmest intervals of the Paleogene.

Eocene bats hunting over Messel maar lake

At twilight over the early Eocene Messel maar lake of what is now Germany, small primitive bats—Onychonycteris finneyi and Icaronycteris index—flutter above the dark, stagnant water as dragonflies skim the surface. Dating to about 47 million years ago, Messel preserves one of the world’s richest records of early Cenozoic life, capturing a warm paratropical forest ecosystem within a volcanic crater lake. The scene highlights some of the earliest known bats, already capable fliers but still retaining primitive features such as the clawed fingers of Onychonycteris.

Oligocene North American woodland with early camels

On a cool Oligocene morning about 30–28 million years ago, an open woodland on the interior plains of western North America is crossed by two swift mammals: the slender early camel Poebrotherium and the long-legged rhinocerotoid Hyracodon. Patchy grasses, sedges, scattered deciduous trees, and distant White River–style badlands reflect a drier, more seasonal world than the lush forests of the earlier Paleogene. This scene captures the growing importance of open habitats during the Oligocene, when many mammal lineages evolved longer limbs and greater speed for life on increasingly exposed terrain.

PETM floodplain mammals in the Bighorn Basin

On a rain-soaked floodplain in Wyoming’s Bighorn Basin during the Paleocene–Eocene Thermal Maximum, about 56 million years ago, small early hoofed mammals forage along a swollen, muddy river after torrential flooding. Dog-sized Hyracotherium—an early relative of horses with four toes on the front feet—and rabbit-sized Diacodexis, among the earliest known even-toed ungulates, move cautiously through driftwood and leaf litter beneath lush broadleaf trees, palms, and ferns. The scene captures the PETM’s intensely warm, humid greenhouse climate, when subtropical forests spread across much of western North America.

Giant Otodus shark hunting in Eocene seas

In the warm outer-shelf seas of the early to middle Eocene, about 56–41 million years ago, the giant lamniform shark Otodus obliquus surges through a school of small teleost fishes, its streamlined body and broad, unserrated teeth marking an early member of the megatooth lineage. Below, a nautilid drifts through plankton-rich water hazed with microscopic foraminifera such as Globigerinatheka, evoking the productive subtropical oceans that spread across much of the Northern Hemisphere during this greenhouse interval.

Transitional whale Ambulocetus in an Eocene estuary

Along the warm Tethyan coast of what is now Pakistan and India, an early whale, Ambulocetus natans, surges through a muddy estuary in pursuit of fish about 50–48 million years ago, during the early Eocene. Its long body, powerful limbs, and broad hind feet reveal a transitional lifestyle: still capable of moving on land, yet increasingly adapted for swimming in shallow coastal waters. Burrow openings of ghost shrimp dot the sandbars nearby, while dense subtropical shoreline vegetation evokes the humid greenhouse world in which some of the first whales evolved.

Paleocene North Atlantic flood basalts and lava eruptions

At the Paleocene–Eocene boundary, about 56 million years ago, fissure eruptions in East Greenland’s North Atlantic Igneous Province poured vast rivers of tholeiitic basalt across a newly rifted coastline. The scene shows incandescent lava fountains, black pāhoehoe and ʻaʻā fields, ash-and-gas plumes, fumaroles, and violent steam explosions where fresh lava meets the sea. These flood basalts formed during the opening of the North Atlantic, a major tectonic episode linked to intense volcanism, crustal stretching, and profound environmental change at the dawn of the Eocene.

Eocene coral patch reef in the Tethys Sea

On the northern margin of the Tethys Sea during the early to middle Eocene, about 56–40 million years ago, a small coral patch reef flourishes in warm, clear shallow water above a carbonate platform. Massive Porites, branching Stylophora, and honeycombed favositid-like corals provide shelter for schools of the moonfish Mene rhombea, while sea turtles such as Eochelone cruise overhead and echinoids and swimming crabs forage among coral rubble and bioclastic sand. This scene reflects the recovery and expansion of reef communities in the Paleogene greenhouse world, when tropical marine ecosystems once again became prominent along the margins of the ancient Tethys Ocean.

Tropics

Eocene Nummulite Carbonate Seafloor Plain

In the warm, shallow waters of the Eocene Tethys, roughly 56–34 million years ago, vast carbonate plains were built by large benthic foraminifera such as Nummulites and the elongate Alveolina, whose shells carpeted the seafloor like coins and grains of rice. Scattered patch corals and calcareous algae punctuate this sunlit shelf, while small batoid rays glide above the sediment in clear aquamarine water. Such environments were major limestone-producing “carbonate factories” of the Paleogene tropics, recording a greenhouse world in which microscopic organisms played an outsized role in shaping marine sediments.

Paleocene Titanoboa and Carbonemys Cerrejón Swamp

In the steamy swamps of Colombia’s Cerrejón Formation, about 60–58 million years ago in the Paleocene, a colossal Titanoboa cerrejonensis glides through tannin-dark water beside the giant turtle Carbonemys cofrinii. Dense palms, ferns, and buttressed flowering trees frame this hot, waterlogged rainforest, a post-dinosaur world where tropical ecosystems had already produced some of the largest reptiles known from the age. The scene captures the lush greenhouse conditions of early Paleogene South America and the remarkable scale of its swamp-dwelling predators.

Eocene Tropical Coral Lagoon and Seagrass

In a warm Eocene back-reef lagoon about 56–33.9 million years ago, clear turquoise water washes over white carbonate sand and patch reefs built by branching Acropora and massive Porites, with pink coralline algae encrusting the reef surface. Grazing regular sea urchins move through seagrass meadows while an early sirenian, one of the primitive relatives of today’s manatees and dugongs, browses in the shallows. Beyond the protected lagoon, nautiloid cephalopods drift near the reef margin, illustrating the rich tropical marine ecosystems that flourished during the Paleogene greenhouse world.

Early Whale Evolution in Tethys Estuary

In this early Eocene estuary along the eastern Tethys, about 50–48 million years ago, an Ambulocetus natans bursts from muddy shallows after a school of fish while more aquatic Rodhocetus cruise the deeper channel beyond. The scene captures a key stage in whale evolution, when archaeocetes still retained strong limbs and broad feet for swimming and moving in coastal habitats, yet were becoming increasingly adapted to life in the water. Silty banks, root-fringed estuarine margins, and humid tropical vegetation reflect the warm monsoonal lowlands of the northern Indian subcontinent, where some of the earliest whales hunted in sediment-rich coastal ecosystems.

Basilosaurus Hunting Dorudon in Eocene Egypt

In the warm, shallow Tethyan sea of Wadi Al-Hitan, Egypt, during the late Eocene about 37–34 million years ago, a giant Basilosaurus isis twists through clear blue water to attack the smaller whale Dorudon atrox. Both animals were early fully marine whales, but Basilosaurus retained the long, serpent-like body of an archaeocete, while Dorudon was more compact and closer in overall form to later whales. Rays rest on the carbonate seafloor below, and sharks cruise in the distance, reflecting the rich marine ecosystem preserved in one of the world’s most famous Eocene whale fossil sites.

Eocene Volcanic Island Rainforest and Basalt

On a tropical Southeast Asian island arc during the Eocene, roughly 56–34 million years ago, rain lashes a coastal rainforest rooted in fresh basalt and volcanic ash beneath towering cliffs of columnar lava. Palms, laurel-like evergreen trees, tree ferns, cycads, and tangled lianas reflect the warm greenhouse world of the Paleogene, while fumaroles and storm-driven surf emphasize the island’s active volcanic setting. Fringing reefs along the shore show that even near restless volcanoes, tropical carbonate ecosystems could flourish in the shallow seas of the ancient Indo-Pacific.

Fayum Primates in African Anthropoid Forest

In the Fayum wetlands of northern Africa, about 34–30 million years ago, early anthropoid primates moved through a dense tropical gallery forest fringing marshy channels and floodplains. Small parapithecids such as Apidium leap among lianas high in the canopy, while the more robust catarrhine Aegyptopithecus climbs more deliberately on thicker branches; below them, the primitive proboscidean Moeritherium browses in shallow reed-filled water. This scene captures the warm, humid Afro-Arabian world of the late Eocene to early Oligocene, when some of the earliest monkeys and apes’ close relatives lived in lush forests alongside archaic elephant kin.

Southern Hemisphere

Giant Eocene penguins hunting fish in Antarctic waters

In the cool coastal seas of Eocene Antarctica, about 40–34 million years ago, giant stem penguins such as Palaeeudyptes and the more heavily built Anthropornis pursue schools of small silvery fish above a soft seafloor scattered with brachiopods, scallops, and sponges. Antarctica was not yet fully ice-covered, and productive green nearshore waters bordered forested polar coastlines. These early penguins, some standing roughly 1.7–2 metres tall on land, show that penguins reached impressive size and ecological diversity long before the modern Antarctic ice age.

Advancing coastal glaciers during Antarctic Eocene-Oligocene transition

At the Eocene–Oligocene transition, about 34 million years ago, Antarctica was entering a profound climatic shift as the first large continental glaciers advanced across its subdued coastal plains. This scene shows bright valley glaciers feeding braided meltwater streams across a gravelly outwash plain, with only sparse, wind-pruned Nothofagus scrub and low mossy ground cover surviving at the margins. It captures the moment when Antarctica changed from a once forested Gondwanan landscape into the cold, ice-dominated continent we know today.

Primitive Eocene marsupials in ancient Australian rainforest

In the warm, rain-soaked forests of early Eocene Australia, about 56–47 million years ago, tiny primitive marsupials climb mossy trunks and fern-covered branches beneath towering araucarian and podocarp conifers. These opossum-like australidelphians, represented here by Djarthia- or peradectid-grade forms, lived in a humid Gondwanan rainforest rich in tree ferns, cycads, and broad-leaved flowering plants. The scene captures Australia during a greenhouse phase of the Paleogene, when lush forests still blanketed much of the continent as it drifted away from Antarctica.

Giant phorusrhacid terror bird hunting in Eocene Patagonia

In late Eocene Patagonia, about 38–34 million years ago, a towering phorusrhacid “terror bird” stalks small Notostylops across an ash-dusted floodplain at the foot of the rising proto-Andes. The scene captures a distinctive South American ecosystem shaped by active volcanism, with muddy channels, thin tuff deposits, and sparse stands of southern beech (Nothofagus) under a hazy sky. Phorusrhacids were among the top land predators of Paleogene South America, while Notostylops was one of the many native hoofed mammals, or notoungulates, that evolved in the continent’s long isolation.

Late Eocene bryozoan colonies on the southern Australian shelf

On a cool-temperate southern Australian shelf in the late Eocene, about 34–38 million years ago, the seafloor is covered by delicate branching bryozoan colonies and pink coralline algae growing over shell gravel and carbonate sand. Among these thickets move thick-spined cidaroid sea urchins, scallops, and small crabs, representing a classic heterozoan carbonate ecosystem rather than a tropical coral reef. Such bryozoan-rich shelves were an important feature of Paleogene seas in the Southern Hemisphere, recording clear, well-lit waters and flourishing invertebrate communities as Australia drifted into increasing isolation.

Primitive whale Llanocetus swimming near the Eocene Antarctic Peninsula

In a storm-darkened subantarctic embayment of the Antarctic Peninsula about 34–36 million years ago, the primitive whale Llanocetus denticrenatus swims just beneath the choppy surface, its large toothed jaws and less streamlined body revealing an early stage in baleen whale evolution. Below, lamniform sharks such as Striatolamia macrota patrol the cold, plankton-rich water, while giant penguins gather near the distant shore. The scene captures Antarctica near the end of the Eocene, when rocky coasts, southern beech and conifer woodlands, and increasingly frigid seas framed a crucial chapter in the origin of modern whales.

Tropical Paleogene coral reefs in northern Australian coastal waters

In the warm greenhouse seas of the early to middle Paleogene, roughly 66–34 million years ago, shallow tropical reefs along northern Australia or southern Africa supported coral communities that already looked surprisingly modern. Branching Acropora and massive Porites built sunlit carbonate habitats crowded with small teleost fishes, scallops, lobsters, and soft sea pens rooted in sandy pockets, while nautiloids cruised above the reef as living reminders of an ancient cephalopod lineage. This scene captures a Southern Hemisphere reef ecosystem during a time when Earth was warmer than today, yet many of the reef-building corals belonged to groups still familiar in modern oceans.

Paleogene Oceans

Giant Basilosaurus hunting Dorudon whales in Eocene seas

In the warm open seas of the late Eocene, about 40–34 million years ago, the giant archaeocete Basilosaurus isis pursues a pod of smaller Dorudon atrox through schools of silvery teleost fish. Unlike modern whales, Basilosaurus had a long, serpentine body, tiny hind limbs, and a narrow tooth-filled skull adapted for seizing large prey, while Dorudon represents a more compact early whale built for agile swimming. A shadowy lamniform shark such as Otodus obliquus below hints at the rich predator community of Paleogene oceans, where early whales had become dominant hunters after the age of marine reptiles had ended.

Giant Anthropornis penguins on the Eocene Antarctic coastline

On a cool Eocene shoreline of the Southern Ocean, giant penguins of the genus Anthropornis—standing roughly 1.5 to 1.8 meters tall—gather along a pebbly coast while others surge through the surf in porpoising leaps. This scene evokes high-latitude Antarctic or subantarctic shores about 40–34 million years ago, when polar regions were much milder than today and bordered by conifer-rich forests with ferns and mossy understories rather than ice sheets. Anthropornis was among the largest penguins ever to live, part of an early radiation of stem penguins that flourished in Paleogene seas.

Shallow Tethys Sea shoals with abundant Eocene Nummulites

In the warm, shallow waters of the early Eocene Tethys, about 50 million years ago, vast carbonate shoals were carpeted by larger benthic foraminifera such as Nummulites and Alveolina, whose abundant shells would later help form famous nummulitic limestones. Browsing among sparse seagrass patches, the early sirenian Eotheroides represents one of the first sea cows, already adapted to life in tropical lagoons but still primitive compared with its modern relatives. Low patch reefs built by corals such as Porites and faviids complete a scene typical of a greenhouse-world tropical shelf sea.

Acidified abyssal seafloor during the Paleocene-Eocene Thermal Maximum

On the abyssal seafloor during the Paleocene–Eocene Thermal Maximum, about 56 million years ago, a dim blue-gray water column hangs over olive-brown mud scattered with the partially dissolved shells of planktonic foraminifera. Sparse benthic animals—such as a brittle star, a small sea cucumber, and a few burrow traces—reflect the ecological stress of warming, acidified, oxygen-poor deep waters, while a Hexanchus-like sixgill shark glides slowly above the bottom. The scene illustrates how rapid carbon release during the PETM shoaled the carbonate dissolution horizon, reducing shell preservation across deep-ocean basins.

Volcanic North Atlantic shelf with basalt cliffs and lava

On the storm-lashed North Atlantic shelf near the Paleocene–Eocene boundary, about 56–60 million years ago, fresh basalt cliffs and steaming lava deltas of the North Atlantic Igneous Province plunge into an ash-choked sea. Floating pumice, dead teleost fishes, and stranded Belosaepia-like cephalopods highlight the ecological disruption caused by intense volcanism during this interval of dramatic environmental change. The scene captures an early Cenozoic coastline in recovery after the end-Cretaceous extinction, where modern-style marine ecosystems were emerging amid powerful tectonic upheaval.

Early whale Ambulocetus in an Eocene Tethyan estuary

In a warm middle Eocene estuary along the Tethys Sea, about 47–43 million years ago, an early whale, Ambulocetus natans, waits half-submerged beside oyster-encrusted mudbanks beneath dense stands of Nypa palms. Nearby, a long-snouted dyrosaurid crocodyliform glides through the shallow brackish channel, while dragonflies skim above tannin-dark water rich with estuarine life. This scene captures a transitional world in which some of the earliest whales still hunted in coastal wetlands, retaining strong limbs and a crocodile-like profile even as whale evolution was beginning its move toward the open ocean.

Next Period

Ice Ages