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NEOMORPHOUS FERCULA?



I'm not going to get excited about a feathered dinosaur 'till I *see* the damn
thing (even if Phil Currie is a theropod-god;)). Pant, slaver.

Achut Reddy tells us...

> Finally, there is a note by Chure and Madsen about finding a
> definite furcula in an allosaurid.  Not sure if this changes
> any current ideas about theropod evolution.

I've read some things recently saying that the avian furcula may be a
neomorph, and is not homologous with clavicles. Yet again, this idea
isn't really at odds with dinosaur cladograms, but it makes for a few
problems. First off, is there any experimental (presumably
developmental) evidence to back it? Secondly, if furculae aren't
clavicle homologues, clavicles must've been lost in bird- ancestors
before furculae appeared.

This makes for a real mess. Why evolve a neomorph when an existing
structure can be exapted for the same function? (Unless you opine that
furculae-bearing birds evolved from clavicle-lacking ancestors, and I
don't think anyone's doing that).  And if clavicles were 'replaced' by
a neomorph, does that mean there were animals going around with *both*
structures for a while, or with neither (the clavicles having been
lost before the fercula appears). Evolutionary saltation
notwithstanding, such a cross-over intermediate stage would hardly
seem beneficial to animals that are supposed to be evolving _flight_
(and the fact that some tetrapods lack both structures is irrelevant).

Of course, I doubt if we really know anything at all about
clavicle-furculae evolution in theropods, given that only a handful of
the animals display them.  As far as I can tell (I've seen Thulborn's
paper* but not the new allosaur one), it's impossible to tell from
theropod furculae whether they are derived from clavicles, or
neomorphic. Right?

* Besides figuring possible furculae in a troodont and _Oviraptor_ (if
memory serves me, the troodont fercula he figures is probably
displaced gastralia - but that doesn't mean that troodonts lacked
furculae of course), Thulborn points to a suspiciously fercula-like
structure in an albertosaur. As for the _Oviraptor_, didn't Osborn
1924 describe them as clavicles? So is it just a matter of
interpretation whether such structures are clavicles or furculae?

Obviously I don't know what I'm talking about - just wondered if
anyone could help.

"Looks like he came in through the south entrance sir.."
Oh dear.

DARREN NAISH