Neogene
Austrian palaeontologist Moritz Hörnes coined the term Neogene in 1853. He defined a span of time that would eventually measure 20.45 million years. This period begins at the end of the Paleogene Period and ends at the start of the Quaternary Period. Geologists divide this vast stretch into two distinct epochs. The earlier epoch is called the Miocene. The later epoch carries the name Pliocene. Some experts argue that the boundary between these modern geological periods remains unclear. They suggest the Neogene cannot be clearly separated from today's world. The older term Tertiary Period once covered this same span of time. That label has fallen out of formal use but persists in informal conversation.
North America and South America connected during the late Pliocene Epoch. A land bridge known as the Isthmus of Panama formed to join them. Warm ocean currents could no longer flow freely from the Pacific Ocean to the Atlantic Ocean. Only the Gulf Stream remained to transfer heat toward the Arctic Ocean. Meanwhile, the Indian subcontinent continued its collision with Asia. This massive tectonic event created the Himalayas mountain range. Sea levels fell significantly throughout the entire period. These drops in water level created new land bridges. One bridge linked Africa directly to Eurasia. Another bridge connected Eurasia to North America. The continents sat very close to their current positions by the end of the era.
Earth entered a warm phase around 11 million years ago. Scientists call this interval the Middle Miocene Climatic Optimum. It was driven by the emplacement of the Columbia River Basalt Group. Around that same time, global temperatures began to drop sharply. The ice caps on both poles started to grow and thicken. Positive feedback loops enhanced this process through increased sea ice formation. Between 7 and 5.3 million years ago, a cooling trend called the Late Miocene Cooling ensued. Decreases in carbon dioxide concentrations drove this shift. A brief warm interval occurred during the Pliocene Epoch between 3.3 and 3.0 million years ago. This peak is known as the Pliocene Thermal Maximum. By the end of the period, the first glaciations of the current Ice Age began.
The reptile group Choristodera went extinct early within this geological span. Amphibians known as Allocaudata disappeared at the very end of it. Terrestrial predators like Langstonia and Barinasuchus also vanished from the fossil record. These creatures were the last surviving members of Sebecosuchia. The oceans became dominated by large carnivores such as megalodons. Livyatans roamed these waters alongside them. About 19 million years ago, approximately 70% of all pelagic shark species disappeared. Marine life took on a modern appearance during these millions of years. Continental flora and fauna evolved into forms recognizable today.
Ungulates in North America increased their stride lengths across the Oligocene-Miocene boundary. They became noticeably more cursorial to adapt to open habitats. An explosive radiation of ursids took place at the Miocene-Pliocene boundary. The first hominins appeared near the end of the period. Tropical plant species gave way to deciduous ones due to cooler seasonal climates. Grasslands replaced many ancient forest ecosystems. Grasses diversified greatly while herbivorous mammals evolved alongside them. Grazing animals such as horses, antelope, and bison emerged. Ice age mammals like mammoths and woolly rhinoceroses were common in the Pliocene. Asteraceae daisies underwent significant adaptive radiation during this time. Eucalyptus fossil leaves appear in the Miocene of New Zealand.
Geologists have long disagreed on where to draw the line for the Neogene Period. The International Commission on Stratigraphy once proposed that the Quaternary be considered a sub-era of the Neogene. Their proposal set the beginning date at 2.58 million years ago. This date marked the start of the Gelasian Stage. The International Union for Quaternary Research counterproposed that the Neogene should end at 2.58 Ma. They argued for key changes in Earth's climate and biota occurring at that specific moment. A compromise reached in 2006 was rejected by the International Union of Geological Sciences. Formal discussions at the 2008 International Geological Congress in Oslo led to a final decision. The ICS decided in May 2009 to make the Quaternary the youngest period of the Cenozoic Era. Thus the Neogene Period ends bounding the succeeding Quaternary Period at 2.58 Ma.
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Common questions
Who coined the term Neogene and when was it defined?
Austrian palaeontologist Moritz Hörnes coined the term Neogene in 1853. He defined a span of time that would eventually measure 20.45 million years.
When did the Neogene Period begin and end according to current geological standards?
The Neogene Period begins at the end of the Paleogene Period and ends bounding the succeeding Quaternary Period at 2.58 Ma. The International Commission on Stratigraphy decided in May 2009 to make the Quaternary the youngest period of the Cenozoic Era.
What major tectonic events occurred during the Neogene Period?
North America and South America connected during the late Pliocene Epoch via the Isthmus of Panama. Meanwhile, the Indian subcontinent continued its collision with Asia to create the Himalayas mountain range.
Which reptile groups went extinct during the Neogene Period?
The reptile group Choristodera went extinct early within this geological span while amphibians known as Allocaudata disappeared at the very end of it. Terrestrial predators like Langstonia and Barinasuchus also vanished from the fossil record.
How did climate change affect flora and fauna during the Neogene Period?
Tropical plant species gave way to deciduous ones due to cooler seasonal climates while grasslands replaced many ancient forest ecosystems. Grazing animals such as horses, antelope, and bison emerged alongside diverse grasses.