Thoughts on Dapingfangornis

[Michael Mortimer <mickey_mortimer111@msn.com>]

I just finished coding Dapingfangornis, so I figured I'd post my thoughts on 
it.

The skull has an odd outline as preserved, but this is due to taphonomy.  
The dorsal snout is either crushed or missing, making the beak seem more 
slender than in life.  The supposed median nasal horn is suspicious.  I 
wouldn't be surprised if it were the standard maniraptoriform laterally 
projected lacrimal 'horn', viewed ventrally.  This would make sense, because 
the frontal's concave upper margin would then be the lateral orbital margin 
in life.  What appear to be parietals are preserved posterior to the skull, 
as seen in the photo of the skeleton (though they aren't illustrated).  The 
ventral margin of the skull is very well preserved, with a maxilla strongly 
resembling Vescornis' and a typical bowed enant-grade jugal with an expanded 
anterior end.  The 'tympanic' is actually one of the few well preserved 
enant-grade quadratojugals.  The described 'palatines' are closer in 
position to pterygoids.  The fenestra posteroventral to the 'nasal horn' 
appears to be a broken or disarticulated space between the frontal and 
nasal/lacrimal.  Two sclerotic plates are apparent, but I don't know what Li 
et al. identified as a vomer or lacrimal.
The dentaries seem to have an elongate posterodorsal process, which combined 
with the surangular's outline, indicate a large external mandibular 
fenestra.  I can't identify what Li et al. describe as a prearticular or 
articular.
The cervical vertebrae are described as heterocoelous, but this could be 
only partial heterocoely.  The presence of at least eight sacral vertebrae 
indicate an ornithothoracine, while the long pygostyle is characteristic of 
basal avebrevicaudans.
The furcula is said to have a short hypocleidium, which would be atypical of 
enant-grade birds (though known in juveniles and Aberratiodontus).  Notably 
there is no other evidence this is a young individual, as the sternal 
posterolateral processes are present, the carpometacarpus and 
tarsometatarsus are fused, and the pygostyle is completely fused.  There is 
a furcula-shaped structure in the illustration, but it's so atypical (one 
clavicular branch more slender and drawn unfused to the rest; hypocleidium 
extends posterolaterally; interclavicular angle comparable to basal 
pygostylians) that either it was drawn exceedingly poorly or not all of it 
is supposed to be a furcula (or both).
The short sternum with fused distal posterolateral processes indicate an 
enant-grade bird.  The anterior margin is more acute than most 
eumaniraptorans, with the exceptions of Longirostravis, Aberratiodontus, 
Cuspirostrisornis, Yanornis and Ambiortus.  The posterolateral processes end 
in small expansions, as in Jibeinia, Protopteryx, Boluochia, Vescornis and 
Aberratiodontus.  However, Dapingfangornis' are apomorphically hooked 
anterolaterally.  The posteromedial processes are very poorly developed, as 
in Protopteryx, Longipteryx and Vescornis (Aberratiodontus lacks them 
entirely).  The posteromedian process is unexpanded, as in Jibeinia, 
Protopteryx, Longipteryx, Boluochia, Vescornis, Eoenantiornis, Sinornis and 
Aberratiodontus.
The illustration would suggest an ulnar sesamoid and three elongate 
metacarpsls (II-IV), but I ascribe this to the artist instead of the 
specimen.  The radius is drawn as much more slender than most Mesozoic 
birds, and this could be due to artistic inaccuracy as well.  The first 
metacarpal as illustrated is longer than any other birds except 
confuciusornithids.  Phalanx I-1 is comparable in length to Jibeinia and 
Enant-grade birds (except Protopteryx, Longipteryx and Eoalulavis).  Phalanx 
II-2 is shorter (compared to II-1) than other coelurosaurs except Jibeinia, 
Vescornis, Sinornis and Eocathayornis.  Metacarpal III is illustrated as 
subequal or barely passing metacarpal II distally, which would be odd for an 
enant-grade bird and more like ornithuromorphs and more basal birds.  It may 
be due to inaccurate illustration.  Digit III seems to only have one 
phalanx, though I wouldn't be surprised if a tiny second one were present 
but not illustrated.  This would be unlike Jibeinia and most more basal 
birds.

Li et al. assign Dapingfangornis to the Eoenantiornithiformes because of a 
short skull, larger nasals and similar sternum.  I disagree.  The 
craniofemoral ratio of Dapingfangornis is 1.22, while Eoenantiornis' is 
1.32.  These are longer than Aberratiodontus (1.07), Vescornis (1.05) and 
Cuspirostrisornis (.99), but comparable to Sinornis (1.22-1.26).  
Protopteryx (~1.42), Longipteryx (1.90) and Longirostrornis (1.80) have 
longer skulls. Even assuming the nasals are correctly identified in 
Dapingfangornis, elongate nasals are primitive for birds.  The sterna are 
not very similar, as noted above.  Eoenantiornis has a more obtuse anterior 
margin, large distal expansions on the posterolateral processes (contra Hou 
et al., 1999), and prominant posteromedial processes.  Li et al. distinguish 
the genera by Dapingfengornis' dubious nasal horn, primitive (and 
overemphasized by taphonomy) sharp snout, apparently short hypocleidium, and 
sternal keel (which is unknown in Eoenantiornis because the sternum is in 
dorsal view; contra Hou et al.,1999).
> From my preliminary comparisons, Dapingfangornis seems most similar to 
Vescornis and Aberratiodontus.  Dapingfangornis resembles Vescornis more in 
gross morphology, and several points of similarity are probably 
symplesiomorphic.  However, the short phalanges I-1 and II-2 would be 
derived.  It differs from Vescornis in many details, including a taller 
jugal and surangular, larger teeth, short hypocleidium, acute anterior 
sternal margin, anteriorly hooked expansions on the sternal posterolateral 
processes, longer posterolateral sternal processes, and elongate metacarpal 
I.  Aberratiodontus shares the same symplesiomorphies with Dapingfangornis, 
but also a couple synapomorphies Vescornis lacks (short hypocleidium, more 
acute anterior sternal margin). Unfortunately, its manus is too poorly 
preserved to tell if it shares the short phalanges I-1 and II-2.  In much of 
its morphology, Aberratiodontus is distinct from other enant-grade birds, 
Dapingfangornis included.  The latter is thus easily distinguished from 
Aberratiodontus, by the shorter snout, probably longer nasals, more 
anteriorly positioned dorsal maxillary process, less numerous dentary teeth, 
short cervical centra, shorter arms, shorter sternum without anterolateral 
processes, posteromedial sternal processes, shorter tibiotarsus and other 
characters.  Aberratiodontus may only be distantly related to other 
enant-grade birds, and it's possible Dapingfangornis is a basal member of 
its lineage.  Vescornis seems most similar to Dapingfangornis, but this 
likely only reflects a gradistic relationship, perhaps as basal members of a 
Cathayornithidae (distinguished by the short manual phalanx II-2).  A better 
description and figures are sorely needed.

Mickey Mortimer