Bird
Birds (class Aves) are feathered, winged, bipedal, endothermic (warm-blooded), egg-laying, vertebrate animals. With around 10,000 living species, they are the most speciose class of tetrapod vertebrates. All present species belong to the subclass Neornithes, and inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from the 5 cm (2 in) Bee Hummingbird to the 2.75 m (9 ft) Ostrich. The fossil record indicates that birds emerged within theropod dinosaurs during the Jurassic period, around 160 million years (Ma) ago. Paleontologists regard birds as the only clade of dinosaurs to have survived the Cretaceous–Paleogene extinction event 65.5 Ma (million years) ago.
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Famous quotes containing the word bird:
“A bird half wakened in the lunar noon
Sang halfway through its little inborn tune.”
—Robert Frost (1874–1963)
“You will believe
a bird flew by the window, a wandering bee
buzzed in the hallway, a wind
rippled the bronze grasses. Or will you
know who it is?”
—Denise Levertov (b. 1923)
“Nor bird nor beast
Could make me wish for anything this day,
Being old, but that the old alone might die,
And that would be against God’s Providence.”
—William Butler Yeats (1865–1939)