The Paleogene Period was a warm geological period from 65.5 to 23 million years ago, characterized by the diversification of mammals and the filling of niches left by the extinction of dinosaurs. Birds, sharks, and whales evolved, while the configuration of continents was similar to today.
The Paleogene Period is a geological period that spans from 65.5 million years ago, when dinosaurs were wiped out by an asteroid, to 23 million years ago, when the period ended with an extensive episode of global cooling. Compared to the present day, the Palogene was a warm period and, as such, is sometimes called “a continuation of the Mesozoic, but with mammals”.
Just as during the Mesozoic, during the Paleogene, the world was warm, with no ice caps, and dense forests extended farther north and south, in places like Wyoming. The Paleogene had high sea levels, but not as high as during the earlier Cretaceous, and except for the inundation of large portions of central Eurasia, the configuration of the continents was much the same as today.
The Paleogene was characterized by the rapid diversification of mammals and the filling of numerous niches left open by the extinction of all non-avian dinosaurs, pterosaurs (flying reptiles) and large marine reptiles (plesiosaurs, mosasaurs, etc.) however, unlike the gigantic dinosaurs that came before them, the early Paleogene land mammals were relatively small, none larger than a bear, and most much smaller, the size of a cat. Larger mammals, such as the rhinoceros ancestors, evolved in the mid-period.
Many of the groups that dominated the Paleogene are extinct today. The puma-like animal Mesonychia is thought to have been a major scavenger or predator of early Palogene. In the early part of the Paleogene cats, pigs and whales evolved. In the middle of the Paleogene, bats, the ancestors of elephants, and Eohippus, the first horse, evolved. Towards the end of the period rodents and the first primates evolved, together with the condylarths, considered the ancestors of modern hoofed herbivores. Various early spin-offs of animals such as the horse, such as Propalaeotherium, whose lineages would have gone extinct without descendants, evolved during this period.
In the skies, birds were busy at work filling the niche left vacant by the death of the pterosaurs. Birds evolved into a variety of fantastic colors, shapes and sizes, by the end of the period reaching a level of diversity similar to today’s. In the oceans, with the death of the ammonites, the predominant mollusk became squid, while sharks grew in diversity and number until they occupied the niches left empty by the disappearance of the large marine reptiles. These were soon joined by whales, which took tens of millions of years to reach their current size.
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