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Preliminary Discussion of Omnivoropteryx and Scansoriopteryx



Though my copy of Czerkas' book has not yet arrived, Mike Keesey was kind
enough to scan me a few images of these new controversial taxa.  Here are my
preliminary opinions-

Omnivoropteryx sinousaorum
This is apparently only shown in X-rays, which allow limited detail to be
discerned.  Description will emphasize comparison to Caudipteryx and
Sapeornis, which Ford and Holtz have posited affinities with respectively.
The skull is thus complete, but sutures are almost impossible to locate.  It
does actually resemble Caudipteryx in gross morphology.  The snout is
shorter and the external nares located more anteriorly.  The snout's ventral
margin is lower than the posterior skull's, the orbit is extremely large,
and the nares are angled sharply anteroventrally.  Those are the only
details available.
The mandible is slender, with a strongly decurved dentary that curves upward
at the very tip.  There seems to be a long and low external mandibular
fenestra, but this is much more posteriorly placed than in Caudipteryx.
A cervical and over ten dorsal vertebrae are preserved, along with dorsal
ribs.  Caudipteryx and other enigmosaurs have ten or less dorsal vertebrae,
while non-pygostylian birds had 12-13.  It's unfortunate the tail was not
preserved.
The scapula is extremely useful in identifying this taxon.  The blade is
sinuously curved, decreases in width posteriorly, and seemingly has no
dorsally
projecting acromion process.  It is extremely similar to Rahonavis in these
features, but differs from oviraptorosaurs like Caudipteryx.  That of
Sapeornis is difficult to compare due to its presevation in lateral view.
The humerus is very elongate and strongly curved.  It resembles that of
Sapeornis in the extent the two can be compared, which is basically
restricted to the outline.  It just may have the characteristic distal spike
on the deltopectoral crest of the latter genus, though the X-ray makes this
unclear.  Humeri of oviraptorosaurs (eg. Caudipteryx, Microvenator) are more
stout and straight (without the strong distal curve).  The radius and ulna
are also similar to Rahonavis- the ulna is strongly bowed, while the radius
is very slender and ends in an abrupt expansion.  Caudipteryx lacks the
disparity in width between the antibrachial elements, and has no marked
distal radial expansion.  Metacarpal I is extremely short (~1/7 of mcII),
like Sapeornis, Jeholornis and other basal birds, but unlike
oviraptorosaurs.  Phalanx I-1 is slender and bowed, only half the length of
metacarpal II.  The reduction is characteristic of derived avians, and the
morphology is most comparable to Sapeornis (and to a lesser extent
Jeholornis).  The whole first digit does not pass the tip of metacarpal II,
like Sapeornis, Jibeinia and ornithothoracines.  Caudipteryx differs in
these characters, with a longer and stouter phalanx I-1, and a first digit
that reaches past phalanx II-1.  Phalanx II-I might have a distal expansion
like Sapeornis, pygostylians and Sinornithosaurus.  Phalanx II-2 is shorter
than II-1, like Jibeinia and ornithithoracines (but unlike Sapeornis).
Phalanx II-2 is bowed and
slender distally, as in avians and approached in some eumaniraptorans (eg.
Sinornithosaurus).  Caudipteryx lacks a distal expansion of II-1, has a
longer II-2 than II-1, and has a more robust less bowed II-2.  The third
metacarpal is closely appressed to the second, like Caudipteryx and
Sapeornis, but unlike Jeholornis.  I see no indication of phalanges, but
Caudipteryx and Sapeornis both have two on that digit in any case.
The pubes are preserved in oblique anterior view.  The pubic symphysis was
reduced (~1/3 of pubic length), like Sapeornis, Jeholornis and pygostylians
(Caudipteryx and other oviraptorosaurs have a ratio of ~1/2).  The pubic
shafts are bent posteriorly a little distal to midlength, as in some
eumaniraptorans (eg. Archaeopteryx, Bambiraptor, Sinornithosaurus), but
unlike the forward curving pubic shafts of oviraptorosaurs.  Finally, the
pubic boot projects completely (or almost completely) posteriorly, as in
eumaniraptorans.  The pubic boot morphology is closest to Archaeopteryx, but
differs from enigmosaurs, which have predominantly anteriorly projecting
pubic boots.  Ilial and possible ischial remains cannot be discerned well.
The bowed femora, tibiae and slender fibulae are too poorly figured to
describe useful morphologies.  The metatarsus is not arctometatarsalian, and
no fifth metatarsal is visible.  The metatarsals are said to be unfused.
The first digit appears reversed, and phalanx I-1 is extremely long and
bowed.  The latter is much longer than non-avian theropods, Rahonavis,
Archaeopteryx, confuciusornithids and most Mesozoic ornithothoracines.  It
suggests perching abilities were well developed.  Phalanx II-2 is subequal
to II-1, as in other eumaniraptorans, but unlike oviraptorosaurs.  The
second digit shows no predatory specializations.  The
distal phalanges of digits III and IV are also elongate compared to the
penultimate phalanges, unlike Caudipteryx and most non-avians (Rahonavis as
well).
Phylogenetic Relationships- The only oviraptorosaur-like characters are the
short snout, ventrally displaced premaxilla and anterior maxilla, decurved
dentary and elongate external mandibular fenestra.  The first is common in
basal birds, especially Jeholornis.  The third is also found in Jaholornis,
while the third is seen in confuciusornithids.  The second character is not
known in eumaniraptorans.
Characters found in basal avians, but not oviraptorosaurs are- more than ten
dorsal vertebrae, scapula decreases in wifth distally, acromion does not
project dorsally(?), distal scapular shaft curved to be concave dorsally,
distal humerus strongly curved anteriorly/laterally, radius about 1/2 of
ulnar width, distal radius abruptly expanded, metacarpal I ~1/7 of
metacarpal II length, phalanx I-1 ~1/2 of metacarpal II length, phalanx I-1
slender, phalanx II-2 distally expanded(?), phalanx II-2 shorter than
phalanx II-1, pubic symphysis ~1/3 pubic length, pubic shafts bent
posteriorly around midlength, pubic boot projects mostly posteriorly,
metatarsal V absent(?), elongate metatarsal I, phalanx II-2 subequal in
length to II-1, distal phalanges of pedal digits III and IV elongate
compared to penultimate phalanges.  While a few of these might be expected
in a convergently volant oviraptorosaur, many have no particular relation to
flight.  So Omnivoropteryx is not a volant oviraptorosaur, but is a
eumaniraptoran instead.
Exactly where within Eumaniraptora Omnivoropteryx should be placed is a
difficult question, as the topology around the avian base is uncertain.  It
is less derived than ornithothoracines based on- scapula not distally
tapered; manual unguals not reduced; phalanx II-2 not as shortened; pubic
symphysis not as reduced.  It shares features with several taxa of basal
birds, notably Rahonavis, Sapeornis, Jeholornis and to a lesser extent
Archaeopteryx, confuciusornithids and Jibeinia.  Thus is will probably end
up slightly more derived than Archaeopteryx, but less than pygostylians.

Scansoriopteryx heilmanni
Scansoriopteryx is very similar to Epidendrosaurus- The specimens are
similar in size, Scansoriopteryx being on average 14% larger (elements 5-22%
larger).  The frontals are nearly identical, strongly triangular with a
V-shaped notch between them posteriorly.  There appears to be a posterior
process on the parietal of Scansoriopteryx, as in Epidendrosaurus.  The
scapula is strongly expanded distally.  The coracoid has a unique C-shape,
approached most closely by Archaeopteryx, but more robust.  The humeri both
have proximally placed deltopectoral crests and are similar in morphology.
The metacarpals and manual phalanges have similar and derived proportions,
with metcarpal III longest, digit III hypertrophied and phalanges III-1 and
III-2 not reduced as in most theropods.  Oddly, both specimens seem to have
an astragalus missing the ascending process aligned with the tibial axis on
a distal edge of the latter.  The metatarsi are very similar, with III
slightly constricted in the middle, but expanding again proximally to equal
its distal width.  Metatarsal I is articulated distally in both.  The pedal
phalanx proportions are similar as well.
I can find the following differences- The parietal is shorter compared to
the frontal in Scansoriopteryx.  The sclerotic ring of Scansoriopteryx is
made of about 14 separate elements, unlike the solid ring in
Epidendrosaurus.  There is no "articular" projecting dorsally in
Epidendrosaurus' mandible.  The distal scapular edge is perpendicular to the
blade axis in Scansoriopteryx.  The ulna of Epidendrosaurus is bowed and the
radius looks thinner in comparison.  The first manual ungual is much larger
than the second in Epidendrosaurus, but not in Scansoriopteryx.
The "articular" of Epidendrosaurus is better seen as a displaced coronoid,
and the distal scapular edge would not be expected to fully ossify in
juveniles.  It's possible the parietals of Scansoriopteryx are not
completely preserved, or have overlapped the frontals.  I cannot explain the
other differences.  I don't believe they warrent generic separation, but
perhaps at species level (especially if the two formations they were found
in are not contemporaneous).
Phylogenetic Relationships- I believe Scansoriopteryx is a basal avialan.
This is based on the following lines of evidence.  The jugal is slender
suborbitally (as in birds), with a posteriorly placed and strongly sloped
dorsal process (resembling Bambiraptor most).  The quadratojugal has a large
posterior process, making it T-shaped.  This process is larger than birds,
being similar to basal deinonychosaurs like Bambiraptor and
Sinornithosaurus.  The ventral postorbital process is extremely thin,
showing it was nearly absent (but still contacted the jugal).  The
triangular frontals are similar to eumaniraptorans, while the posterior
parietal process is like that of Sinornithosaurus.  Assuming the
Epidendrosaurus mandible is correctly referred, the teeth lack serrations
and are mediolaterally thick, like avians.  Although the strong and medially
curved dentary symphysis is like oviraptorosaurs, the posterodorsal dentary
process is not elongate and the external mandibular fenestra is not as
enlarged as oviraptorosaurs.  The ninth and more posterior chevrons are
strongly flattened dorsoventrally (as in eumaniraptorans), but not as
elongate as Jeholornis or dromaeosaurs.  They are nearly identical to those
in Archaeopteryx and Rahonavis.  The caudals with flattened chevrons also
elongate to over twice the length of the first caudal centrum, similar to
dromaeosaurs, but less than Archaeopteryx, Jeholornis and Rahonavis.
Prezygopophyses are elongate, extending to half the proceeding central
length.  This is much less than dromaeosaurs, but is a bit more than
Jaholornis, and much more than Archaeopteryx and Rahonavis.  The coracoid is
elongate (but not strut-like) and curved posteriorly, being most similar to
Archaeopteryx.  The ilium has an extremely elongate preacetabular process,
like Rahonavis and avians.  It has a slight ventral expansion, like
Rahonavis and Unenlagia.  The postacetabular process on the other hand, is
strongly reduced, as in Rahonavis and Aves.  The pubis is mesopubic as
preserved, like Archaeopteryx, Jeholornis and especially Unenlagia and
Rahonavis.  The pubic boot is reduced, as in troodontids and
Sinornithosaurus.  The distally placed and seemingly reversed hallux is
similar to avians.  Pedal phalanx II-2 is elongate relative to II-1, as in
eumaniraptorans.
There are several characters distinctly unlike avialans and basal
eumaniraptorans (distally expanded scapula, elongate ischium, ischium
strongly posteriorly concave, no dorsal ischial processes), but I feel these
are overwealmed by the other characters noted above.
Regarding integument- there are tuberculate scales preserved with the distal
tail of Scansoriopteryx, and elongate ulnar feathers/filaments (~1.5 times
ulnar length).  There is also filamentous integument associated with the
skull, pelvis and proximal tail.  I don't see why adult Scansoriopteryx
could not potentially fly.

Those who want pictures of Omnivoropteryx (skull, feet, and whole specimen)
and Scansoriopteryx (skull, whole specimen) e-mail me offlist.

Mickey Mortimer