naked heads (was: Re: Velociraptor Animation)

["Aspidel" <aspidel@wanadoo.be>]

HP "David Marjanovic" <david.marjanovic@gmx.at>
> And why doesn't it have feathers on its head?>

HP Tim Williams wrote:
> The correlation for scavenging birds having naked heads and necks is
pretty
good: vultures from the Old World (Accipitridae) and New World (Vulturidae /
Cathartidae) show this feature, as does the carrion-eating marabou stork
(Ciconiidae).  Thus, bare heads evolved at least twice in the Aves (three
times if it evolved independently in the marabou and its kissing cousins,
the vulturids.) >

So, why not some dromaeosaurs with a naked head and others, like cf.
_Sinornithosaurus_ with a feathered head?
Friendly - Luc J. "Aspidel" BAILLY.