[no subject]

[Nick Longrich <nrlongri@midway.uchicago.edu>]

I dragged up the Yandangornis paper just now. My thoughts-
        This is a maniraptoran. The elongate fourth toe is a surefire way
to tell a maniraptoran, along with some details of the deltopectoral crest
(assuming the reconstruction is accurate), the bowed ulna, the very short
chest relative to femur length, and what appears to be a wrist folded back
at least 60 degrees, implying a semilunate (although this is illustrated as
not preserved).
        This animal does have  a beak, but it doesn't look like an
oviraptorosaur. The manual claws are too small, and the fourth toe is too
long. Oviraptorosauria, Caudipteryx, and their probable sister-taxon
Protarchaeopteryx all have symmetrical feet in which the fourth toe is
subequal to the second. Therizinosaurs, dromaeosaurs, troodontids,
Rahonavis, archaeopteryx, Confuciusornis all have a long fourth toe. In
addition, the tail vertebrae are all wrong. Although they are not
hyperelongate as in Archaeopteryx, troodonts, and Rahonavis (something I
think could argue for a Deinonychosauria-Rahonavis Archaeopteryx clade I
suspect might exist) they are too long and slender to be from the
therizinosauroid-oviraptorosaurian clade. Additionally, the beak is more of
a V-shape than a U-shape, again unlike therizinosaurs and oviraptorosaurs.
The sternum doesn't look oviraptorosaurian as reconstructed. The tail is
distally flexible and shows no evidence of a pygostyle, unlike the strongly
locking distal caudals of Caudipteryx. The transverse processes appear to
become reduced or absent after about 5 vertebrae; this was not a
Caenagnathid/Oviraptorid but this argues it was maniraptoran.
        The animal does not appear to be an
Archaeopteryx-Therizinosaur-Oviraptorosaur-Deinonychosaur grade
maniraptoran. The sternal ribs are very long and slender, as in modern
birds. The tarsometatarsus is described as distally fused; this is found in
Changchenornis in MT III and IV but not in Confuciusornis according to
Chiappe et al. The manual unguals are unusally small. The lateral sternal
processes do not project laterally as in oviraptorids and dromaeosaurs, but
rather project posteriorly as in Confuciusornis and modern birds. The
sternum is narrower than in Archaeopteryx-grade maniraptorans, but it is
also narrower than Confuciusornis.
        The animal does not appear to be a confuciusornithid or pygostylia.
It lacks the autapomorphic hole in the deltopectoral crest found in
Confuciusornithidae. Pygostylian features lacking are a pygostyle,
reduction of the ungual of the manual major digit, it lacks the
flattenening of the major digit seen in pygostylians.
        Conclusions?
        This animal appears to nest in an extremely interesting place in
the avian tree.

It is maniraptoran based on:
 * reduced number of transverse processes (12-13 or fewer)
 * very low chest/femur length ratio
 * elongate digit IV
 * ?semilunate
 * ?bowed ulna

 It appears to be more derived than velociraptor-archaeopteryx grade
animals in having:
 * elongate sternal ribs (actually, not in Confuciusornis so maybe not a
good character)
 * reduced manual unguals
 * shortened manual phalanx II-2,
 * posteriorly pointing sternal processes.

it appears to fall outside of Confuciusornithidae+Ornithothoraces in lacking:
* pygostyle
* nublike manual ungual II
* flattened manual digit II

Habits:
        Approximate wingspan: 40-50 cm. guestimated with some crude
calculations, assumptions of bone and feather lengths, and joint angles, or
~1.5 ft. Depends on how long you make the primaries.This seems adequate to
get an animal of ~17 cm trunk length and ~30 cm, or one foot, acetabulum to
ground. The femur is longer than the humerus it appears (there is some
breakage through the femur). The toes are pretty stubby(only half the
length of the tarsometatarsus instead of about the same length as in
Confuciusornis) and have relatively short distal phalanges with shorter toe
claws than in Confuciusornis: this animal was pretty terrestrial, as the
long hindlimbs argue, the fact that the tarsometatarsus is longer than in
Confuciusornis (itself argued to be semiterrestrial), and the manual
unguals look worse for climbing than in Confuciusornis.
        Admittedly, this is all based on illustrations that don't look to hot.
        So what was it doing? I think this was a ground bird, albeit one
with a relatively high wing-loading. It doesn't have super-long gull wings
but they look large enough to get it off the ground; in addition the ulna
probably would have been shorter than the humerus and at least these days
that indicates relatively high wing loading for reasons that elude me.
        It dovetails nicely into the discussions of takeoff. How did this
animal get off the ground? I doubt it did so by jumping.
        Look at these jump-starters: starlings, pigeons, galliformes. In
other words, not birds with relatively *low* pectoral masses, like
Yandangornis probably was given the size of the sternum, but birds with
some of the *highest* pectoral masses- up to 1/4 of body weight- among
Aves. In addition, these things have highly specialized supracoracoideus
pulleys, and I don't know that Confuciusornithid-grade things did.
Low-speed ground takeoff is really energetically demanding and it seems
like early birds would have played around with less-demanding flight
strategies until they were more specialized- i.e. at the higher speeds that
can be achieved with a taxi, or by dropping out of a tree. The morphology
of this thing seems to rule out leaping out of trees as a habit (since it
looks highly terrestrial), and it is also relatively large, where again
flight becomes more demanding- so I think it taxied, like ducks, puffins,
albatrosses, etc. to get up to speed where it could get airborne. In
addition, the humerus: the humerus is long, slender, sigmoidal. Not like
pigeons, chickens, even confuciusornis, where it is relatively high in
diameter and straight, i.e. built to take lots of torsional stresses
imposed by powerful pronation-supination required at low-speeds and during
ring-vortex flight, as opposed to the simple dorsoventral flapping with
less extreme wing rotation seen in fast-forward continuous-vortex flight
(I'm just talking out of my @$$ here of course, I'm unaware anyone's done a
study on this, and yes there are exceptions- swifts, e.g. which would
appear to use humeral rotation to achieve continuous-vortex flight and so
have these bizarrely pterodactyloid-like humeri)
        Just for the record, I'd guess that this ground-takeoff was
derived, not primitive.
        Anyways, my thoughts, for what it's worth coming from some crude
line drawings.