Mammals' Triassic Origins
Mammals originated during the late Triassic period, around 225 million years ago. They descended from a group of reptiles called synapsids, distinguishing themselves with fur and specialized teeth.
Jurassic Period Diversity
During the Jurassic, mammals were small, nocturnal, and diverse. They exploited ecological niches, ranging from insectivores to early herbivores, coexisting with dominating dinosaurs.
Cretaceous Mammalian Expansion
In the Cretaceous, mammals remained small but began to diversify into more ecological roles. Some developed gliding and swimming abilities, showcasing early adaptability in various environments.
Mass Extinction Opportunities
The Cretaceous-Paleogene extinction 66 million years ago, which extinguished the dinosaurs, allowed mammals to rapidly diversify and occupy newly vacant niches, leading to large-bodied forms.
Eocene's Placental Boom
The Eocene epoch witnessed the rise of placental mammals, which came to dominate over marsupials outside of Australasia. This era introduced early primates, whales, and hoofed animals.
Ice Age Megafauna
The Pleistocene epoch, known for its Ice Ages, saw the evolution of impressive megafauna like the woolly mammoth and saber-toothed tiger. These large mammals adapted to cold climates but many became extinct as the climate warmed.
Human-Induced Changes
In recent millennia, humans have significantly influenced mammalian evolution through domestication, habitat alteration, and climate change, impacting species diversity and distribution.Mammal Egg-Laying Ancestors
Some early mammals, like the platypus, still lay eggs, a trait inherited from their reptilian ancestors, defying the typical live birth characteristic of most mammals.
When did mammals originate?
Late Triassic period
Early Jurassic period
At Cretaceous beginning
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