Surprise! Jeholornis palmapenis isn't valid.

What's that you say?  ANOTHER supposedly new Jehol basal avialan is just a junior synonym of a known species?!  Shock!  Gasp!  This time it's none other than the armless Jeholornis palmapenis (insert priapic joke here).  On the plus side, at least the description is better than others so far published, so this will help when coding Shenzhouraptor sinensis for matrices.

O'Connor et al. (2012) listed several characters supposedly distinguishing this taxon from Jeholornis prima.

The single preserved maxillary tooth and second empty alveolus contrast with IVPP V13274 (the prima holotype), V13550 and V13553 (both referred to prima), which have been reported to lack maxillary teeth. Yet jeholornithid teeth are often unpreserved due to their small size and low number, as seen by palmapenis' lack of dentary teeth (considered preservational by O'Connor et al.) and LPM 0193's (the Shenzhouraptor holotype) lack of any recognizable teeth. Even palmapenis only preserves one of the at least two maxillary teeth it had on that side. Thus the absence of maxillary teeth in other specimens may easily be preservational.

The presence of two pairs of anterior dorsal pleurocoels was listed as diagnostic (grading into a single pair posteriorly), but pleurocoel number often varies between different vertebrae and even sides of the same vertebra in theropods. Anterior pleurocoel number has not been described in any other jeholornithid specimen, but IVPP V13353 shows single pairs in dorsals nine and eleven, and three pairs in ten. Until palmapenis is shown to be consistantly unique in pleurocoel number, this character is not considered diagnostic.

Comparison of palmapenis ilium (top; after O'Connor et al., 2012) with prima (bottom; after Zhou and Zhang, 2003).  Note the ventral edge of the postacetabular process (blue) is not significantly more concave in palmapenis.  Note also the obvious breakage of the ilium (circled in red), making the dorsal border look highly convex.  The upper right picture shows superimposed and flipped images of the anterior left ilium and posterior right ilium to show the dorsal margin (surrounded by green) is straight.  Note that when the dorsal margins are lined up this way, the preserved posteroventral portion conveniently follows the outline of the other pubic peduncle.

The ilium is supposedly strongly convex dorsally, but it's clear the anterodorsal portion has merely been broken off, with no dorsal margin remaining anterior to the acetabular midpoint. The margin posterior to this is slightly convex as in other jeholornithid specimens. The anterior dorsal margin is preserved on the disarticulated left ilium, which forms a similar overall ilial dorsal convexity to other jeholornithids when rotated into place. Similarly, though the postacetabular process was described as strongly concave ventrally, the concavity is almost identical to that in IVPP V13353 (20% distance from line stretching from top of acetabulum to ventral postacetabular tip is 20% of ilial depth above acetabulum, compared to 19%) and other jeholornithids (the supposedly straight margin of IVPP V13274 looks slightly curved in the photo, and any difference would be insignificant in any case).

The dorsally curved ischium was also said to be diagnostic, but the distal ischium is unpreserved in the prima holotype, with the reconstructed portion being part of the tibia or fibula instead. Indeed, O'Connor et al. state ischial curvature is unclear in other Jeholornis specimens. LPM 0193 shows a dorsally curved ischium, albeit less so than in palmapenis.

In the tail, the transition point was stated to be more gradual (in central elongation) and posterior (at caudal seven instead of six) in palmapenis than IVPP V13550. Yet the transition point is also different in IVPP V13353, where the first elongated caudal is five, and IVPP V13274, where it seems to be at four (an unlabeled caudal is disarticulated adjacent to the last sacral). Differences in transition point abruptness are present as individual variation in other taxa, such as two nearly identical Microraptor specimens (CAGS 20-7-004 and 20-8-001), where the difference between lengths of caudals three and four is 9% in one and 53% in the other). Both caudal differences are thus more probably individual variation.

Finally, the diagnosis lists "elongated caudals possess chevrons with hooked articulations", but these articulations are not mentioned again and photos show normal, straight dorsal, anterior and posterior ends as in other paravians.

Of the diagnostic characters listed for prima by O'Connor et al., the ones not mentioned above are all unknown in palmapenis (except the robust dentary, which is true for all jeholornithids). In the text, the dentaries are said to appear unfused unlike the prima holotype, but they note this may be due to poor preservation. It may also be due to ontogeny, as palmapenis is smaller and has an unfused metatarsus. The text also states the ilium differs in having a bround rounded preacetabular process supposedly unlike IVPP V13274, but this is due to the latter being in medial view and not showing the ventral flange that would be lateral to the cuppedicus fossa, as seen in IVPP V13353 and LPM 0193.

So of the listed differences from prima, only the difference in maxillary dentulousness can even be plausibly considered true and not subject to individual variation. Ironically there are some valid differences not mentioned in the text. The dentary is a third deeper than the prima holotype and IVPP V13350, which is opposite the expected trend for a juvenile. The ischium slightly expands at its tip, unlike the Shenzhouraptor holotype. But since the first difference is not observable in the Shenzhouraptor type (whose anterior dentary angles beneath the skull) and the second difference is not observable in the prima type (whose distal ischium is broken off), these would form a weak differentiation from either species. As both character states are derived in Avialae, Shenzhouraptor and prima could not be united by their counterpart states. Instead, until they are shown to have a consistant variation between multiple specimens, the differences are more readily ascribed to individual variation as is found in any theropod known from large sample sizes (Allosaurus, Tyrannosaurus, Microraptor, Archaeopteryx). Jeholornis palmapenis is here made a junior synonym of Shenzhouraptor sinensis.

Referennces- Zhou and Zhang, 2003. Jeholornis compared to Archaeopteryx, with a new understanding of the earliest avian evolution. Naturwissenschaften. 90, 220-225.
O'Connor, Sun, Xu, Wang and Zhou, 2012. A new species of Jeholornis with complete caudal integument. Historical Biology. DOI: 10.1080/08912963.2011.552720