Re: No more paedomorphosis

[Dinogeorge <Dinogeorge@aol.com>]

In a message dated 98-04-18 09:36:17 EDT, m_troutman@hotmail.com writes:

<< I was using the point of the ischium as an example of how it is 
 that Rahonavis was a bird. Rahonavis also has a laterally facing 
 glenoid, more closely appressed metatarsals, and a slimmer tibiotarsus 
 than most dromaeosaurs.  >>

By itself, the ischium is bologna, but when you throw in the scapula, you're
getting somewhere. I took another look at the scapula in the _Rahona[vis]_
paper and it's indeed quite a bit more avian than the scapula of ordinary
dromaeosaurids. I can't imagine that scapula reversing to the form it has in
flightless dromaeosaurids (not to mention that their skulls aren't very avian,
either). So _Rahonavis_ is higher up the avian tree than I first thought. This
has an interesting implication: the dromaeosaurid foot, with its enlarged
second-digit ungual, is beginning to look like an avian  symplesiomorphy
(secondarily lost in _Archaeopteryx_ and in avialan birds), not a
dromaeosaurid and/or troodontid synapomorphy. Maybe this is why the big claw
occurs in troodontids, which are otherwise not very similar to dromaeosaurids.
Either that, or there's massive convergence going on, or essentially the
entire hindquarters of _Rahonavis_ reversed to the dromaeosaurid form--and if
you believe that, I have this bridge to sell you...

I'm getting tired of these perfunctory analyses. What needs to be done is a
careful assessment of all the characters that have been thrown around various
recent papers on theropod and dinosaur systematics. Take a look at the
monograph on amiid fish that just appeared with last week's issue of JVP;
there's nothing like that for >any< dinosaur group, and there sure needs to
be: 1500 photos and line drawings, revision of the entire taxonomy--and this
is just for >one< family. Something you can sink your teeth into, if you're
interested in amiid fish.