A field guide to mesozoic birds and other winged dinosaurs

Feathers & Wings
Feathers are classified based on their anatomy, their location
on the body, and their function. There are two primary types of feathers.
Pennaceous feathers have a rigid central filament or “quill” called a rachis
(plural: rachides), from which stems numerous smaller filaments called
barbs, linked together into a coherent vane by tiny barbules and microscopic
hooklets. This arrangment of barbs, barbules and hooklets allows the
vane to separate and to be “zipped” back together in a manner similar to
Velcro. Plumulaceous or “down” feathers have short central filaments and
barbs that lacks barbules and hooklets, preventing the formation of vanes
and rsulting in soft tufts. Down feathers are usually present as an insulating
layer below the contour feathers of a bird. Pennaceous feathers of the wing
are called remiges (singular: remix), and those of the tail are called rectrices
(singular: rectrix). Body feathers are called contour feathers, and are generally
more loosely arranged and softer, though still vaned and pennaceous.
In Mesozoic birds as in modern birds in general, the feathers on
the bottom of the head often began at or before the same point as the upper
feathers, and were often long, creating a round-headed appearance.
Similarly, most feathered fossil birds show very long feathers on the neck.
Though long depicted as sinewy and slender, the necks of most maniraptorans
were buried in feathers and would have appeared very short when
not fully extended.
In most modern birds, the metatarsus and toes are bare and scaly,
with scutes covering the top of the foot. This seems to have been the case
in most Mesozoic birds as well, except for the most primitive. Many of the
basal-most birds had long feathers on their legs and shorter feathers covering
the toes. It may be that the first feathered animals were completely
covered in feathers and subsequently re-developed scales only on the legs.
Alternately, feathered legs may have been a genetic consequence of the development
of hind wings in some species.
It is common to refer to bird-like dinosaurs or early birds having
“arms” and “hands”. However, many of these species possessed fully formed
wings. Rather than being something present “on” the arm or hand, wings
incorporate the entire forelimb. The primary feathers of the wing anchor to
the the first few phalanges and the metacarpals of the forelimbs, and so are
as much a part of the “hand” as the claws are. Ligaments anchor the wing
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