Birds (Class Aves) are a group of highly successful, primarily flying vertebrates, which are descended from theropod dinosaurs. They have a fossil record stretching back 150 million years (late Jurassic), but until recent discoveries were made, significant gaps existed in this record. Nowadays we have a good understanding of bird evolution through the Mesozoic, but relationships amongst modern birds are largely unresolved. There are 153 families (over 9000 species) of living birds, of which 134 have fossil representatives, and there are another 77 extinct families known.
Author: Robert Davis
Last updated: 21/11/05
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