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| | Scarlet Robin, Petroica boodang| Scarlet Robin, Petroica
boodang Birds (class Aves) are winged, bipedal, endothermic
(warm-blooded), egg-laying, vertebrate animals. There are around
10,000 living species, making them the most varied of tetrapod
vertebrates. They inhabit ecosystems across the globe, from the
Arctic to the Antarctic. Extant birds range in size from the
Template:Convert/cmTemplate:Convert/test/Aon Bee Hummingbird to
the Template:Convert/LoffAonDbSoffTemplate:Convert/test/Aon
Ostrich. The fossil record indicates that birds evolved from
theropod dinosaurs during the Jurassic period, around 150–200 Ma
(million years ago), and the earliest known bird is the Late
Jurassic Archaeopteryx, c 150–145 Ma. Most paleontologists
regard birds as the only clade of dinosaurs to have survived the
Cretaceous–Tertiary extinction event approximately 65.5 Ma.
Modern birds are characterised