The fossil record indicates that birds evolved from feathered ancestors within the theropodgroup, which are traditionally placed within the saurischian dinosaurs, though a 2017 paper[4] has put them in a proposed clade Ornithoscelida, along with the Ornithischia. True birds first appeared during the Cretaceous period, around 120 million years ago.[5] DNA-based evidence finds that birds diversified dramatically around the time of the Cretaceous–Palaeogene extinction event 66 million years ago, which killed off the pterosaurs and all the non-avian dinosaur lineages. Birds, especially those in the southern continents, survived this event and then migrated to other parts of the world while diversifying during periods of global cooling.[6] Primitive bird-like dinosaurs that lie outside class Aves proper, in the broader group Avialae, have been found dating back to the mid-Jurassic period, around 170 million years ago.[1] Many of these early "stem-birds", such as Archaeopteryx, were not yet capable of fully powered flight, and many retained primitive characteristics like toothy jaws in place of beaks, and long bony tails.[1]

Birds have wings which are more or less developed depending on the species; the only known groups without wings are the extinctmoa and elephant birds. Wings, which evolved from forelimbs, gave birds the ability to fly, although further evolution has led to the loss of flight in flightless birds, including ratites, penguins, and diverse endemic island species of birds. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds, have further evolved for swimming.

Some birds, especially corvids and parrots, are among the most intelligent animals; several bird species make and use tools, and many social species pass on knowledge across generations, which is considered a form of culture. Many species annually migrate great distances. Birds are s

The fossil record indicates that birds evolved from feathered ancestors within the theropodgroup, which are traditionally placed within the saurischian dinosaurs, though a 2017 paper[4] has put them in a proposed clade Ornithoscelida, along with the Ornithischia. True birds first appeared during the Cretaceous period, around 120 million years ago.[5] DNA-based evidence finds that birds diversified dramatically around the time of the Cretaceous–Palaeogene extinction event 66 million years ago, which killed off the pterosaurs and all the non-avian dinosaur lineages. Birds, especially those in the southern continents, survived this event and then migrated to other parts of the world while diversifying during periods of global cooling.[6] Primitive bird-like dinosaurs that lie outside class Aves proper, in the broader group Avialae, have been found dating back to the mid-Jurassic period, around 170 million years ago.[1] Many of these early "stem-birds", such as Archaeopteryx, were not yet capable of fully powered flight, and many retained primitive characteristics like toothy jaws in place of beaks, and long bony tails.[1] Birds have wings which are more or less developed depending on the species; the only known groups without wings are the extinctmoa and elephant birds. Wings, which evolved from forelimbs, gave birds the ability to fly, although further evolution has led to the loss of flight in flightless birds, including ratites, penguins, and diverse endemic island species of birds. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds, have further evolved for swimming. Some birds, especially corvids and parrots, are among the most intelligent animals; several bird species make and use tools, and many social species pass on knowledge across generations, which is considered a form of culture. Many species annually migrate great distances. Birds are s

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Stock photo: The fossil record indicates that birds evolved from feathered ancestors within the theropodgroup, which are traditionally placed within the saurischian dinosaurs, though a 2017 paper[4] has put them in a proposed clade Ornithoscelida, along with the Ornithischia. True birds first appeared during the Cretaceous period, around 120 million years ago.[5] DNA-based evidence finds that birds diversified dramatically around the time of the Cretaceous–Palaeogene extinction event 66 million years ago, which killed off the pterosaurs and all the non-avian dinosaur lineages. Birds, especially those in the southern continents, survived this event and then migrated to other parts of the world while diversifying during periods of global cooling.[6] Primitive bird-like dinosaurs that lie outside class Aves proper, in the broader group Avialae, have been found dating back to the mid-Jurassic period, around 170 million years ago.[1] Many of these early "stem-birds", such as Archaeopteryx, were not yet capable of fully powered flight, and many retained primitive characteristics like toothy jaws in place of beaks, and long bony tails.[1] Birds have wings which are more or less developed depending on the species; the only known groups without wings are the extinctmoa and elephant birds. Wings, which evolved from forelimbs, gave birds the ability to fly, although further evolution has led to the loss of flight in flightless birds, including ratites, penguins, and diverse endemic island species of birds. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds, have further evolved for swimming. Some birds, especially corvids and parrots, are among the most intelligent animals; several bird species make and use tools, and many social species pass on knowledge across generations, which is considered a form of culture. Many species annually migrate great distances. Birds are s was taken by pnvcreation on 25-12-2015 with Panasonic model ELUGA I . DPI width: 72.0, height 72.0 . White balance settings: 0.