Phanerozoic/Neogene period

by David DeGuzman

Neogene: 23 MYA (Million Years Ago) - 1.3 MYA

The Neogene Period lies in the Cenozoic Era, which lies in the Phanerozoic Era. The Neogene Period starts 23 mya, after the Paleogene Period and ends at 2.6 mya when the Quaternary Period begins.

Epochs

The Neogene Period is divided into two epochs.

Miocene 23 - 5.33 mya.

This epoch is translated as "less recent." This is the longest epoch of the Cenozoic Era. This is also considered a high point for mammals as mammal diversity reached its peak. The beginning of the Miocene Epoch marks the end of prehistoric times and the birth of a world that is more "recent."

Pliocene 5.33 to 1.83 mya

Translated as "more recent." During this epoch, the world transforms similar to the world today. This also marks the beginning of the evolution of prehistoric man. It is often divided into no two parts:

Early Pliocene

This section consists of the Zanclean Age. The Zanclean begins at 5.33 Mya and lasts for about 1.73 million years.

Late Pliocene

This section consists of Piacenzian and Gelasian Ages. The Piacenzian begins 3.6 Mya and lasts 1.01 million years and the Gelasian begins 2.59 Mya lasting .78 million years ago.

Climate

The climate during the Neogene became colder and drier. During the Miocene, the drifting of continents caused the isolation of both poles from other continents. This then established the circumpolar ocean circulation. As a result, more sunlight was reflected from the Earth and sea levels dropped causing a reduction in temperatures. This caused the Antarctic cap to grow gradually. This cooling continued into the Pliocene and the Pleistocene.

In other areas, the world began to dry out. In North America and Central Asia, massive deserts had developed. The forests were replaced by arid plains, steppes, prairies, and tundras. Grasses that were low in nutrition but abundant in tooth-decaying materials flourished in place of forests. Transformations such as these forced species to either adapt or surrender their lives.

Plate tectonics

A great event that occurred the Cenozoic Era caused the Tethys Sea (between Eurasia from Gondwana) to be converted into mountains and plateaus. Tectonic activity that began in the Eocene Epoch continued into the Pliocene to create the northern front of the Alps as well as the Apennines, Carpathians, Caucasus, and the Himalayas. The tectonic activity resulted from large-scale folding and thrust-faulting as the African block hit the western underside of Europe. In the Miocene, India collided with Asia that created plateaus and ranges to higher elevations, creating the Himilayas. This was marked by extensive volcanism, folding, thrusting, and emplacement of granitic plutons. At the same time, the Rocky Mountains and Andes Mountains formed in North America and South America respectively.

South America continued to move north towards North America, creating the Panama Isthmus in the Pliocene Epoch. Due to the drops in sea levels, the bridge was exposed to open air creating a path for animals from South America to migrate upward into North America.

Map of Basin and Range Province

In North America, a large area was created called the Basin and Range Province. It covers an area from Nevada and western Utah to central Mexico. This was named this due to the alternating basins and mountain ranges. This alternation is caused by the stretching of the Earth's crust:

1. The region uplifted during the Mesozoic Era.
2. In the Miocene, the arch subsided between normal faults.
3. Uplifted blocks formed mountain ranges that became a source of sediment that filled adjacent basins.
4. Faults opened fissures exposing molten rock from below which produced extensive lava flows.
5. Erosion of fault blocks and mountains filled basins, clogged rivers, and created lakes behind debris dams.
6. Gypsum and salt layer formed when lakes dried.

There are numerous hypotheses to explain this stretching of the crust.

• The subducted spreading center, caused by North America moving over the Pacific oceanic plate and a spreading center that was being subducted along the coast of California, caused uplift and stretching.
• Normal faulting in the area is how the crust adjusted to the change along the California coast when oblique shearing of the edge of the continent.
• The area is extension and uplift of crust from remnants of an oceanic plate carried beneath the Basin and Range region by an earlier subduction zone.
• Crustal extension and tensional faulting is related to convectional movements beneath the continental plate similar to those that cause continents to separate.

Although these hypotheses have varying ideas, each has evidence that can support their claim, meaning the truth can be one of these or a combination of them.

Plant Life

Two ecosystems were introduced during the Miocene period: kelp forests and grasslands. Kelp is a brown algae that grows in cool waters. It is one of the fastest-growing plants on earth. This plant was most abundant in areas where it can attach to rocks and coral. Due to the cooling climate, tropical and conifer forests were reduced to grasslands and savanna. Grasslands were abundant in silica that break down teeth. As a result, animals were forced to adapt quickly to new types of food. Angiosperms (plants with flowers) flourished and diversified all through the Neogene.

Animal Life

The climate changes that occurred caused many animals to adapt or die out. The formation of grasslands provided little nutrients for herbivores to eat. Furthermore, the grass was extremely harsh on teeth. Because of drought, starvation, and cold weather, herbivores were either eliminated or forced into transformation. They developed teeth that are flat and durable for grinding grasses. Other species developed multiple stomachs to squeeze as many nutrients as possible from the grasses. Animals that developed these traits, the artiodactyl, include camels, bison, sheep, and giraffes. Predators as well were forced to change as the number of prey decreased significantly. Predators now have to follow and hunt prey that is spread extremely thin across the lands. As a result, predators became skilled in hunting, developing skills in death strikes, speed, and powerful tools such as sharp teeth and bone-breaking jaws to compensate.

Both prey and predators began to adapt to open-air areas. Small bodied animals began to flourish as it was easier for them to hide and hunt in the low grasslands. Small bodied prey included rodents, raccoons, rabbits and possums and predators included foxes, cats, dogs, and snakes.

Tectonic shifts also assisted in the diversification in certain areas. In North America and South America, dogs, cats, bears, and horses traveled south while armadillos, porcupines, ground sloths, and opossums migrated north.

Megalodon artist depiction

Among these adaptations, some species did not have to change drastically to compensate for conditions. Humans and bears fall into this category. Judging from merely their appearances and genetics, one can infer that these two species should have fallen victim to the changing Earth. However, they were able to utilize behavioral adaptations to make up for the shortcomings.

Smilodon a.k.a. saber-toothed cat

Megafauna

The megafauna, or "large mammals", peaked during the Miocene epoch. Examples of megafauna include horses, rhinos, mastodons, and saber-tooth cats. Due to human activity and climatic changes, many of the megafaunas have died out. Giant sharks were also present that preyed on early whales. One example is the Carcharodon megalodon. Recent speculations measured this massive beast to be around 40 - 50 feet long. This shark was estimated to live during the Miocene and Pliocene Epochs. Although the estimation of their sizes seems quite large, this is merely based on only the size of their teeth. Unfortunately, their bodies are presumed to have a skeleton made up of cartilage, a material that rarely fossilizes well if at all.

Human Evolution

Human development is traced from the Early Pliocene to the present. Hominid lineages were first found in the valleys of north-east Africa. Hominids evolved from Australopithecines that lived in Ethiopia and Tanzania. The erect postures provided them ways to scout for potential threats and freed their hands for using tools. The large-brained australopithecines then evolved into the first stage of man called Homo habilis in the Early Pleistocene. Later in Pleistocene, hominids began to expand in overall cranial size, providing more room for larger brain size and developing intelligence. The emergence of Homo Erectus gave the stepping stone for Homo Neanderthals and Homo Sapiens(modern man).

Homo Neanderthals vs Cro Magnon (Homo Sapiens)?

Neanderthal reconstruction

The typical appearance Neanderthal looked very similar to the present man with only a few defining characteristics. They were typically short and stocky and had an oval-shaped skull. The center of their faces was large with a huge nose and angled cheekbones. In overall body size, Neanderthals were more strong and compact and capable of efficiently conserving body heat, making them able to live in any kind of climate change. In terms of intelligence, their brain size was quite identical to ours if not larger. Like us, they were able to use tools, create and use fires, and even bury their dead. In short, Neanderthals were stronger and possibly more intelligent than the modern man.

So the question arises, "if the Neanderthals were so similar to us in terms of strength, intelligence, and overall survival skills, how did they become extinct?" Although there are plenty of hypotheses and theories to develop an explanation for this mystery, there are no definitive arguments that solve it. Some theorize that they had simply evolved quicker into the modern man while others hypothesize a huge conflict between the Sapiens and Neanderthals, though there is no evidence of any sort of battle or war between them. Currently, there is still extensive research that is being put into solving the mystery of the disappearance of our not so distant ancestors. So far, nothing is truly definitive.