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Jehol/ornis and (Natl Geo) dromaeosaurs
Some more comments on Jeholornis as well as contemporary dromaeosaurs,
including the note in the latest (May) Natl Geo.
The Naturwissenschaften and original Nature paper claim that Jeholornis has a
reversed hallux, but the only photo I've seen that clearly shows the hallux
(Fig. 1A bottom foot) clearly shows the it unreversed as in the contemporary
dromaeosaurs. If other inner toes are reversed then this suggests the hallux
was actually intermediate and pointed one way or another depending on the
circumstances of preservation, unlike Arch in which the toe always ends up
reversed on the slabs. In any case the lack of revesal of at least one first
toe further strengthens the link between theropods and birds and dromaeosaurs
and basal birds, and confirms massive mosaic evolution, while throwing yet
another lug wrench into the the increasingly metal screeching and grinding
gears of conventional cladistics. Things keep going like this a pretty soon
there will be no characters consistently shared by Arch and birds and not
found in dinosaurs! Oh happy days.
I wonder about the citation of Wellnhofer as pers comm that the sternum of
Archaeopteryx may be unfused. Checked the original description and it sure
looks fused to me. I suspect miscommunication.
That Jeholornis has a distal tail fan of feathers at the end of a very long
(both in count and length) stiffened tail like that of contemporary flying
dromaeosaurs is very interesting, and suggests that this represents a
widespread if not general stage of avian flight above the level of
Archaeopteryx, rather than being limited to basal dromaeosaurs.
Which brings us to the Natl Geo note on the new biplane dromaeosaur
specimens. I found it annoying. The photo is perhaps the best resolution yet
published, and it makes very clear that the mid and inner feathers of both
wings are as long and therefore as broad in chord as those of Archaeopteryx
and modern birds (same true in other specimens), and would have overlapped
the leg wing. The inner leg feathers are similarly long (same in other
specimens). So the accompanying illustration repeats the error of narrow
chord inner wings of the type one might expect in a glider. That in every
respect the flight apparatus of these dromaeosaurs is as or much more
advanced than that of Archaeopteryx is not noted.
The central finger appears to be free of feathers, which is entirely
incorrect. The entire length of the finger helped bear the outer array of
primaries (longer than that of Archaeopteryx) as the finger does in
Archaeopteryx in other birds. Only the claw was exposed. The pelvis is shown
as shallow when the specimens show it was deep.
As for the hindwing posture problem, well preserved femoral heads of the
Jehol dromaeosaurs are spherical in a manner dramatically different from
other dinosaurs and birds, and most specimens are preserved spread eagled
with the femora still articulated in the hip sockets, showing the legs could
splay out to the side to make the wings wings. Since Archaeopteryx specimens
are never preserved this way, and are flipped on their sides like dinosaurs,
they had normally dino-avian erect legs and could not use their legs as
wings, which makes sense since they lacked big leg feathers.
Which brings us back to Jeholornis. So far as I know the wing feathers are
not preserved. Nor any leg feathers. Since it had the dromaeosaur rather than
Archaeopteryx type tail one wonders if jeholornids had leg wings. But the
specimens seem to be preserved on their sides in the Archaeopteryx manner.
We'll just have to wait for more specimens.