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search  Neognaths (Neognathae) are birds within the subclass
Neornithes of the class of birds. The Neognathae include
virtually all living birds; their sister taxon Palaeognathae
contains the tinamous and the flightless ratites.  There are
nearly 10,000 species of neognaths. Since the late Cretaceous,
from which the earliest fossils are known, they have undergone
an adaptive radiation producing the diversity of form, function,
and behavior that we see today. The Passeriformes (perching
birds) are the largest order of land vertebrates, containing
some 60% of living birds and being more than twice as specious
as rodents and about 5 times as specious as Chiroptera (bats and
flying foxes) which are the largest orders of mammals. On the
other hand, there are some very small orders, usually birds of
very unclear relationships like the puzzling Hoatzin.