Neogene Earth – Human Ancestors

Neogene Earth

23.03 to 2.58 Million Years Ago

Jay Matternes

A scene depicting Early Neogene (Miocene) fauna, including early horses and carnivorans, as well as now extinct taxons such as entelodonts and chalicotheres.

We’re nearing the present day in our epic journey through the history of the Earth. This was a time when the world started to closely resemble that which we know today. A cooling land and greater seasonal variation across the world would lead to the rise of many of the biomes that persist to this day. In Part 14 of my ‘Journey through the History of the Earth’, we’ll be exploring the rise of many common modern mammals as well as the first hominids, our own direct ancestors.

Part 1: Hadean Earth – The Violent Creation of Our World

Part 2: Archean Earth – Signs of Life

Part 3: Proterozoic Earth – The First Animals

Part 4: Cambrian Earth – An Explosion of Evolution

Part 5: Ordovician Earth – Colonising a Barren Land

Part 6: Silurian Earth – The First Breath of Air

Part 7: Devonian Earth – The Age of Fishes and Forests

Part 8: Carboniferous Earth – The Age Bugs

Part 9: Permian Earth – The Age of Amphibians

Part 10: Triassic Earth – The Rise of the Dinosaurs

Part 11: Jurassic Earth – The Land of Giants

Part 12: Cretaceous Earth – The Reign of Tyrants

Part 13: Paleogene Earth – The Rise of Mammals

Part 14: Neogene Earth – Human Ancestors

Part 15: Quaternary Earth – The Age of Man

For 43 million years, mammals had been enjoying their rise to dominance across all the Earth’s major ecosystems. Many of the modern mammalian orders were already well-established by the beginning of the Neogene but, as global climates started to change and new environments arose, the animals would change too. As the world was starting to cool, vast swathes of grasslands appeared, giving rise to entirely new environmental niches that had never before been seen on Earth.

By traditional definition, the Neogene Period ended 2.58 million years ago, but this has been the subject of much controversy in recent years. As such, some timescales do not include the present geological time at all, instead including it in the Neogene. However, for the purposes of this series, we’ll be sticking with the current definition as outlined by the International Commission on Stratigraphy. Neogene means ‘new genesis’, owing to the rise of many modern animals during this time.

Highlights

• First hominids evolve
• Large horses appear
• Seasonal variation increases
• Insects diversify
• Modern Mediterranean forms
• Ice Age Begins

Newly Formed Biomes Hail in a New Era of Mammalian Dominance

Pixabay

Grasslands, such as the African savannah shown here, appeared during the Neogene, giving rise to many new types of grazing animal.

Whereas the preceding Palaeogene Period was characterised by a relatively warm greenhouse climate with high oxygen levels, the world cooled significantly during the Neogene. The Miocene Epoch is the first of the two epochs that make up the Neogene, and it carries on the trend of increased seasonal variation and global cooling brought in during the preceding Oligocene Epoch.

Throughout the Neogene, in fact, the global climate was quite similar to what we know today. Oxygen levels eventually dropped to their current levels, and CO2 levels dropped to some of their lowest ever levels since the appearance of multicellular life on Earth. By the end of the period, they had reached about 280 parts per million, remaining relatively stable until the beginning of the Industrial Revolution.

Thanks to the reduced effect of global warming, the world cooled, forming environments and greater seasonal variation. When we look at, for example, the humid, tropical and thoroughly alien world of the Carboniferous some 360 million years ago, there’s little to compare with the Neogene and the closely related modern world. Now was a completely different time and an unrecognisably different world where entirely new biomes could thrive.

The Miocene world is characterised by the appearance of two completely new biomes in fact. Grasslands expanded to form steppes and savannahs much like those found today in places like Mongolia or South Africa respectively. This new biome gave rise to whole new families of grazing animals, including the first horses, rhinoceroses and giraffes. New carnivores came along to prey upon these herbivorous grazers, such as cats, bear-dogs and hyenas. At the same time, almost all the modern plant genera that persist to this day appeared.

Pixabay

Kelp grew in great abundance in cooler coastal areas, forming underwater ‘forests’ and whole new biomes in the process.

Kelp forests formed another never-seen-before biome in coastal regions of the Earth’s oceans. These vast underwater forests of brown algae proliferated greatly, supporting entirely new species of fish and aquatic mammals such as otters. They also thrived, as they do today, in more temperate areas of the world, rather than replacing the coral groves and seagrass beds of tropical regions.

Modern Animals Replace Archaic Groups

Heinrich Harder

Hypohippus, which closely resembles modern equines, lived in North America during the Miocene.

While many archaic mammals looked very different to their modern counterparts, many modern mammalian orders continued to evolve during the Miocene, replacing many of the older groups in the process. Birds also followed the same trend, with most modern genera also appearing during the Miocene. Hyracodonts, a once extremely successful family of mammals that included the titanic paraceratherium, disappeared during the early Miocene. Oreodonts and entelodonts also declined throughout the Miocene, giving way to newer and more successful taxons.

Horses were just one family that underwent a major change in their evolution during the Miocene. No longer were they the tiny dog-sized creatures that there were some 50 million years ago. By the late Miocene, some 8 to 10 million years ago, they already grew as large as modern ponies and closely resembled their current, domesticated counterparts. Numerous other taxons joined them in their evolutionary march forward, including the direct predecessors to modern antelopes, elephants and countless other species.

Charles R. Knight

Early mammalian families, such as the cat-like nimravids and the protoceras, declined and ultimately disappeared during the Miocene.

Although the first true cats had appeared towards the end of Oligocene, the Miocene saw them spread and diversify across much of the globe. The related feliforms, known as nimravids, also known as false sabre-toothed cats, started to decline, eventually going extinct in the Late Neogene. Around 20 million years ago, pseudaelurus evolved, the first species of which was only about the size of a domestic cat. However, this animal, dubbed ‘almost a cat’, is now believed to be the direct common ancestor of lions, tigers and leopards, as well as the now extinct smilodons.

Early canines, another member of the carnivoran order, also enjoyed great success during the Miocene as the direct ancestors to foxes and wolves appeared. Other carnivorans, such as mustelids (weasels, badgers, otters and ferrets etc.), bears and civets, also thrived throughout the epoch. The now extinct amphicyons, also known as bear-dogs, continued their role as apex predators throughout the Neogene and even well into the current Quaternary Period until their disappearance 1.8 million years ago.

Human Ancestors Arise from Primates

Pixabay

Chimpanzees might share 99% of their DNA with modern humans, but they’re a much older genus, having evolved 7 million years ago.

Primates first appeared some 55 million years ago, but these archaic primates were relatively small arboreal creatures including early lemurs, monkeys and tarsiers. However, our very own human ancestors also appeared in the beginning of the Neogene Period, evolving rapidly throughout the Miocene. These were the first hominids, the taxonomic family we share with orangutans, gorillas and chimpanzees.

To this day, we share around 99% of our DNA with chimpanzees, one of the most intelligent species of the animal kingdom. It remains our closest living relative, but that doesn’t mean we have as much in common as some people think.

Chimpanzees and humans turned down separate evolutionary paths between 5 and 7 million years ago, nearing the end of the Miocene Epoch. At this time, two of the hominid genera, pan (chimpanzees) and homo (humans) drifted apart, although there may have been a degree of hybridisation between the two until as recently as 4 million years ago.

Matheusvieeira

Widely regarded a the direct ancestor to the homo genus, to which modern humans belong, australopithecus lived between 4.5 and 2 million years ago.

Around 4.5 million years ago, during the early Pliocene Epoch, australopithecus evolved, the genus from which, it is believed, modern humans ultimately arose. What is most fascinating about these animals is that they were very much the missing link between apes and humans. While they shared various characteristics with modern humans, such as walking on two legs, they had significantly smaller brain sizes and are not believed to have mastered the use of tools beyond an extremely basic level.

By the final stage of the of the Pliocene, the second and last epoch of the Neogene Period, the genus of homo evolved, probably from the australopithecines. Exactly which species of australopithecine early humans arose from remains unknown. Nonetheless, the genus homo is partly defined as the first hominids to use stone tools, which occurred during the last stage of the Neogene.

Great Migrations Redefine Evolutionary Paths

Jay Matternes

Many among the Pliocene fauna, such as that depicted here, radiated across much of the world as new land bridges opened between Eurasia and North America.

The Pliocene is the last of two epochs that make up the Neogene Period. It ended with the arrival of the current geological period 2.58 million years ago. As is the case with the names of most geological times, the name Pliocene comes from Greek, roughly meaning a continuation of the recent. With most modern genera in place and an increasingly modern climate, the Pliocene world was more like the one we live in today than any before it.

The Pliocene was a time of abundant migration as sea levels continued to fall as they had done throughout the Miocene. This led to the formation of new land bridges, including one crossing the Bering Strait between Asia and North America. Many ancestors of common modern mammals, including the early horse hipparion, crossed over into the Americas during the Pliocene.

South America had long been isolated from the rest of the world until the Late Pliocene, when tectonic activity formed the volcanic isthmus of Panama. As such, many North American and Eurasian orders invaded that continent. However, the same also happened in reverse, making for a major event known as the Great American Interchange. Until this time, South America had spent tens of millions of years in isolation, allowing unique groups of animals to appear, much as was the case with Australia.

Rom-diz

Sparassodonts, like the thylacosmilus depicted here, formed a successful order of predatory marsupials endemic to South America and lasting over 60 million years. However, their fate was sealed by the Great American Interchange, and they disappeared 3 million years ago.

The Great American Interchange saw many iconic species, both fossil and current, move between the two continents. Others, however, failed to survive the onslaught, which had catastrophic effects on many species, particularly the endemic South American marsupials. One of the most famous of these casualties were the carnivorous sparassodonts, which had evolved shortly after the extinction of the dinosaurs 66 million years ago. Though these peculiar animals looked superficially like sabre-tooth cats, they were in fact metatherians, making them a sister taxon to the marsupials.

Some famous examples of Pliocene animal migration include that of early horses, giant ground sloths (megatherium) and giant armadillos (glyptodonts). Camelids are a particularly interesting case, however. This group, which now includes llamas, alpacas and camels, were originally endemic to North America, but used the newly formed land bridges to migrate to South America and Eurasia. Oddly, their modern distribution is virtually the opposite of their area of origin, for no camelids alive today are native to North America.

Paubahi

During the Pliocene, the Mediterranean Sea was completely cut off from the Atlantic, allowing animals to freely roam between Europe and Africa.

Life in and around the Mediterranean Sea also changed dramatically during the Late Neogene. Between the Miocene and Pliocene Epochs, much of the Mediterranean Sea dried up, and what was left had a much higher salt content. Known as the Messinian Salinity Crisis, the event had a devastating effect on local ecosystems, while also presenting new migratory opportunities to various species. As such, early elephants and hippopotami migrated into the newly formed valleys between Africa and Europe, and there was an increased interchange between species of both continents. However, by the end of the Neogene, the Atlantic Ocean reclaimed the area, forming the modern Mediterranean Sea.

Conclusion

We have now travelled through near 4.7 billion years of Earth’s history to arrive at the border between the old and the new, the boundary between the last geological period and our own. 2.58 million years ago, the Neogene drew to an end as the world cooled and the Ice Age began. The series of glaciations that followed would greatly influence the path of evolution, but it would also be the time when mankind rose to dominance. Next week, we’ll be exploring the rise of modern man in the final instalment of the series.