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Re: Rahonavis; sickle claws



> >Seriemas (_Chunga_ and _Cariama_) do have a sickle-claw on the second
toe.
> >So do certain phorusrhacids (e.g. _Psilopterus_).  Cariamids and
> >phorusrhacids are gruiform birds, so the presence of an enlarged
sickle-claw
> >may be a shared derived feature.
>
> But seriemas have curved claws on pedal digit III and IV too. [...]
> So, what is the difference with regard to size and degree of claw
> arc curvature between digit II and the others in seriemas?

Unfortunately I can't give any quantitative measurement now, but the claw on
toe II is much bigger than the others. There's a stuffed specimen in the
museum here, I'll have a look sometime.

Harpyias (and, I was told in the latest thread on this topic, many other
birds of prey) also have enlarged claws II. The respective toes are not
hyperextensible, though; I don't know for seriemas. The meanwhile famous
claws of cassowaries are just lengthened, not more curved than the other
ones (means, pretty straight), and AFAIK the toes are not hyperextensible
either.
        *Confuciusornis sanctus* (fine specimen in the same museum) likewise
has distinctly enlarged claws II (curved as expected in a perching bird).
Neither relative size nor curvature are as extreme as in "dromaeosaurs" and
*Rahonavis* (hey, come to think of it, I don't know enough about
troodontids...). I can't tell whether the toe was hyperextensible (means, I
can't see greatly enlarged articular surfaces, means, _I think_ it was not).
        There were rumours that *Ornitholestes* also had such a thing. What
has become of that?
        Many coelurosaurs have shorter mt II than mt IV like
*Archaeopteryx*, which _might_ tell of a reduced sickle claw, but the toe
itself is never suspicious.

> [...] Deinonychus ant[ir]rhopus [...]