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Zhongonris the juvenile confuciusornithid?
Tom Holtz wrote-
> CHUNLING GAO, LUIS M. CHIAPPE, QINJING MENG, JINGMAI K. O'CONNOR, XURI
> WANG, XIAODONG CHENG and JINYUAN LIU. 2008. A NEW BASAL LINEAGE OF EARLY
> CRETACEOUS BIRDS FROM CHINA AND ITS IMPLICATIONS ON THE EVOLUTION OF THE
> AVIAN TAIL. Palaeontology 51: 775-791. 10.1111/j.1475-4983.2008.00793.x
While coding Zhongornis I wondered if it could be a case analogous to
Liaoxiornis- a juvenile misinterpreted as a basal taxon. The specimen is
obviously juvenile, based on the lack of carpometacarpal, synsacral,
tibiotarsal and tarsometatarsal fusion, carpal and sternal ossification, and
bone texture. As Yates noted in his blog entry (
), juvenile enantiornithines also have well developed remiges and retrices
(Chiappe et al., 2007) and thus these prove nothing about whether adult
Zhongornis would retain its apparently primitive features as an adult. Gao et
al. find four characters place Zhongornis basal to Pygostylia-
70. Distal caudal vertebrae not fully fused into a pygostyle. This is also
true of juvenile enantiornithines such as Dalingheornis and IVPP V14238.
71. More than eight free caudal vertebrae. This is due to the fact adult
pygostylians fuse several vertebrae into their pygostyle, so is ontogenetic AND
correlated with the previous character.
203. Posterior trochanter not hypertrophied. Bony processes are well known to
enlarge with growth of the organism (e.g. sternal processes, pubic foot,
cnemial crest in enantiornithines).
209. Tibiotarsus unfused. This is also seen in juvenile enantiornithines and
So there's no convincing evidence placing Zhongornis outside Pygostylia. If it
is a member of a known pygostylian group, confuciusornithids are the most
obvious choice. For one, they're the only pygostylians that retain the
elongate third manual digit. The only characters Gao et al. use to exclude
128. Deltopectoral crest not enlarged and quadrangular. It's true that the
deltopectoral crest is lower than in adult confuciusornithids, but this is also
true of juvenile confuciusornithids like Eoconfuciusornis. Juvenile
enantiornithines also have lower deltopectoral crests than adults. And while
the crest of Zhongornis IS lower than adult confuciusornithids, it's higher and
more quadrangular than most Mesozoic pygostylians.
172. Manual ungual II not reduced compared to manual ungual I. This is true
and while it could be ontogenetic, there's no reason to assume it is.
173. Phalanx III-1 not much shorter than III-2 or III-3. Zhongornis is
supposed to have a manual phalangeal formula of 2-3-3, which would be unlike
confuciusornithids. However, the base of digit III is hidden beneath phalanx
II-1. If there is a phalanx III-1, it would have to be short, as in
Dalianraptor and confuciusornithids. And even if it really is absent, a
reduction to nothingness is still a reduction and could count as having the
231. Untwisted metatarsal I. I'm not sure how certain this is in Zhongornis.
Metatarsal I doesn't look very different from that in Confuciusornis (Chiappe
et al., 1999 figure 44) to me.
The general morphology of Zhongornis otherwise resembles confuciusornithids.
This includes proportions of elements as well as the complete toothlessness.
It's possible the specimen really does represent a new near-pygostylian taxon,
but at this point I feel an identity as a juvenile confuciusornithid is more