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Re: 11th specimen of Archaeopteryx



>Tim Williams wrote:

> AFAIK, metatarsal I is straight and the hallux is fairly high, as in
> _Archaeopteryx_.  If so, _Jeholornis_ could not have had a reversed
> hallux suitable for grasping.

OK, but Li and Zhang (2008) looked at the taphonomy and anatomy of several
specimens just to answer this question. They found the ungual curvature
was 113.1 degrees, and that metatarsal I has undergone some morphological
changes that result in a partially reversed hallux.

Li, Z. & Zhang, Y. 2008. Reconstructing the habits of Jeholornis prima.
In: Abstracts of the 7th International Meeting of the Society of Avian
Paleontology and Evolution, Sydney, 18-22 August 2008, p. 11

The habits of Jeholornis are reconstructed based on measurements of pedal
claw arcs, reexamination of the
reversed hallux and statistic analysis of the major hindlimb bone
proportion. The average curvature of the
pedal claw of digit III in five specimens of Jeholornis is 113.1°, similar
to that of extant perching birds.
Since early avians were usually two dimensionally preserved, the
recognition of the reversed hallux in the
most basal birds, e.g., Archaeopteryx and Jeholornis, is often
controversial. Our observation shows that
during the evolution of a reversed hallux, the first phalanx of pedal
digit I had undergone some
morphological changes to enable the initial reversal of the hallux, prior
to the medial rotation of metatarsal I
as seen in most modern birds. The orientation of the phalanx I-1 is
assumed to have contributed to the
reversal of the hallux. Three-dimensional reconstruction method is also
applied in the identification and
reconstruction of the disputed orientation of the hallux in Jeholornis. By
comparing the feet in various
individuals of Jeholornis, we notice that the observed direction of the
hallux seems to be related to the
preservational process of the pedal digits to some extent. The hallux
tends to be preserved as opposed in
ventral view, but not opposed in dorsal view. We conclude that Jeholornis
generally possessed a reversed
hallux, though not well developed as in more advanced birds. Ternary
diagrams are used to analyze the
relative contribution of the three main segments (femur, tibiotarsus,
tarsometatarsus) to the total hindlimb
length in Jeholornis and other basal birds, indicating a pattern of
progressively increased arboreality and
change in locomotion style in early avian evolution. In conclusion, the
above-mentioned evidence suggests
that Jeholornis was arboreal or mainly arboreal in habit.