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Figure 1:In mammals, the quadrate and articular bones are small and part of the middle ear; the lower jaw consists only of dentary bone.. While living mammal species can be identified by the presence of milk-producing mammary glands in the females, other features are required when classifying fossils, because mammary glands and other soft-tissue features are not visible in fossils.
The timeline of the evolutionary history of life represents the current scientific theory outlining the major events during the development of life on planet Earth. Dates in this article are consensus estimates based on scientific evidence , mainly fossils .
Dinosaurs are a diverse group of reptiles [note 1] of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is a subject of active research.
As they evolved in synapsids, these jaw bones were reduced in size and either lost or, in the case of the articular, gradually moved into the ear, forming one of the middle ear bones: while modern mammals possess the malleus, incus and stapes, basal synapsids (like all other tetrapods) possess only a stapes.
“Evolving during the rule of the dinosaurs left a lasting legacy in mammals,” de Magalhães wrote. “For over 100 million years when dinosaurs were the dominant predators , mammals were ...
Dinosaurs evolved from more primitive reptiles in the aftermath of Earth's biggest mass-extinction event caused by extreme volcanism at the end of the Permian Period about 252 million years ago.
The book chronicles the evolution of dinosaurs, their rise as the dominant clade, and ends with an account of their extinction from the Chicxulub asteroid. It also includes a discussion of the evolution of feathered dinosaurs and birds' descent from dinosaurs, and an epilogue of sorts discussing the post-dinosaur emergence of mammals.
Mammals in particular diversified in the Paleogene, [29] evolving new forms such as horses, whales, bats, and primates. The surviving group of dinosaurs were avians, a few species of ground and water fowl, which radiated into all modern species of birds. [30] Among other groups, teleost fish [31] and perhaps lizards [23] also radiated.