The Neogene period, which began 23 million years ago, had more species than today due to human-caused extinctions. South America had unique fauna, but many became extinct as animals from North America traveled south. The ongoing ice age of the Neogene is characterized by glacials and interglacials, increasing aridity, and the replacement of forests by grasslands. Large animals were common during the Neogene, including mammoths, hippos, and cave bears. Competition with cave hyenas slowed human migration across the Bering Strait.
The Neogene is the geological period that began 23 million years ago and extends to 2.6 million years ago or to the present day, depending on which scientist you ask. Because it occurred relatively recently or is still ongoing, Neogene organisms tend to be mostly similar to those of today, but with several important differences. Because humans have caused the extinction of thousands of species since we began spreading across the world 60,000 years ago, the Neogene historically had more species than we observe today.
During most of the Neogene, the continents were mostly in their present positions, although South America was disconnected from other continents and did not connect with North America until 3 million years ago. South America had some of the most unusual fauna on the planet, dominated by marsupials, including large carnivorous marsupials, xenartran (armadillos, anteaters, and sloths, including the elephant-sized Megatherium), and a unique and diverse group of native ungulates , most of which became extinct as animals from North America traveled south and outnumbered the native fauna.
The Neogene Period is characterized by an ongoing ice age, which began around the beginning of the period and continues to the present day. It has been punctuated by glacials and interglacials, periods in which continental glaciers cover large parts of North America and Eurasia and other periods in which they retreat to Greenland and Antarctica. In contrast to earlier warmer and wetter periods, the Neogene is characterized by increasing aridity and the replacement of forests by grasslands. Therefore, many of the organisms characteristic of the Neogene are ruminants, animals that ruminate, an adaptation to extract more energy from grass.
While large animals are relatively rare today, they were much more common during most of the Neogene. Eurasia was settled by numerous mammoths, including the woolly mammoth. Parts of Europe and the Near East were settled by animals traditionally associated with Africa, such as hippos, water buffaloes, lions and cheetahs. Most of the caves of Eurasia were filled with hostile animals such as the cave bear or cave hyena. Competition between humans and cave hyenas is thought to have slowed our migrations across the Bering Strait by thousands of years.
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