Re: Archaeopteryx not the first bird, is the earliest know

[David Marjanovic <david.marjanovic@gmx.at>]

From: GSP1954@aol.com
Date: Sat, 03 Dec 2005 11:36:16 -0500 (EST)

> Archaeopteryx is fast losing its status as the all important "urvogel"
> taxon around which centers our understanding of bird origins, which is
> logical since our data base is dramatically expanding.

I agree (of course)...

> Archaeopteryx still stands as the first and most basal known flying
> dinosaur/member of the avian clade, but that is an accident of discovery 
> that will change at some point.

Both parts of this sentence depend on the phylogenetic definition of Aves.

> unless the bird revolved a long tail (not sure where this leaves
> Jeholornis).

I can't imagine the long tail of *Shenzhouraptor* (senior synonym) (and 
the apparently distinct *Jixiangornis*) is secondary. I can't tell it 
apart from that of *Rahonavis*, and both of those are very similar to that 
of Archie itself.

A well-illustrated description of *Yandangornis* would help a lot, of 
course...

> The Thermopolis specimen also shows something important about limb
> posture. Like all the other complete Archaeopteryx specimens, it is
> preserved on its side, flattened laterally. One leg is also in normal
> pose in that it projects ventrally from the hip, the other leg is
> clearly disarticulated dorsally. This consistent pattern is compatible
> with the cylinderical hip socket of Archaeopteryx which did not allow
> the legs to splay out strongly. Some of the Jehol dromaeosaurs are also
> preserved on their sides showing they could adopt an erect
> leg posture, but many if not most are preserved dorso-ventrally crushed
> with the legs splayed out to the sides. I have not seen a Jehol
> dromaeosaur with a truly cylinderical femoral head like those seen in
> the flightless velociraptorines, they are always somewhat more rounded
> in shape. This indicates that the winged dromaeosaurs could splay their
> legs out much more than normal in theropods, although not necessarily
> entirely flat.

I disagree.

Have a good look at fig. 9 of Hwang et al. (2002) (preferably in the pdf 
at a magnification of some 200 %, and on a good screen...). You will see 
that both ilia are broken lengthwise. Their dorsal halves are vertical 
(consistent with the preservation of the specimen in dorsal view), but 
their ventral halves are horizontal, still in the same plane as the femora 
(the left femur even looks articulated, though its head is not visible -- 
presumably it points downward into the slab). Apparently it was easier to 
break the ilia than to disarticulate the legs by applying pressure to 
them! IMHO this is evidence _against_ any ability for leg abduction.

Besides, a round head isn't enough; if it continues to be at a 90° angle 
to the shaft, it will hardly change anything, especially if the acetabulum 
doesn't change -- and apparently the acetabulum didn't change.

IMHO the various postures, breakages and disarticulations are best 
explained by fossilization under different speeds of sedimentation (thus, 
different pressures at points when different amounts of soft parts were 
still there). This would also provide a neat explanation for why some 
*Confuciusornis* specimens are preserved in lateral view (great photo in 
DA!) while most are in dorsal or ventral view.

> This makes sense since they had leg wings. I find attempts to explain
> how these hindwings were deployed without sprawling the legs highly
> dubious.

I can imagine the foot feathers pointing laterally and forming a small 
"third wing" (the feet pointing forward, horizontal, parallel and close to 
each other) -- microraptors as biplanes, with two sets of wings above each 
other. (More, actually, like the Red Baron's triple-decker with its small 
fourth wing between the wheels.) But I don't know where this leaves the 
tibial and femoral feathers. Perhaps they pointed caudally and avoided 
turbulence behind the long legs? Perhaps they just enlarged the display 
surface?

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