Sorry, I'm *really* speaking of Patago*pteryx*. Please have a look at Classifications|Avialae|Ornithurae|Patagopteryx in http://dinosauricon.com. Anyway, thank you for information about Ornitholestes and Megaraptor (and I simply forgot Noasaurus, you know, so sickle claws have evolved more than once).
The type specimen of Patagopteryx doesn’t have toes (only a few phalanges) preserved. So how can it have a sickle claw? There is no indication for it.