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Re: 11th specimen of Archaeopteryx



You are correct, that's Phalanx I 1, not the metatarsal. The message
stands, though, that this team assembled to examine the specimens and
considered various options and found modifications of the 1st toe (1st
Phalanx) that allowed partial reversal of the hallux.


> Jason Brougham <jaseb@amnh.org> wrote:
>
>> 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.
>
>
> This abstract is very interesting.  Nonetheless, it mentions
> morphological changes of phalanx I-1, not metatarsal I.  In Li and
> Zhang's words: "... 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."
>
>
> This is tantalizing, but not especially informative when it comes to
> said "morphological changes".  The hallux of _Jeholornis_ (and
> _Archaeopteryx_) is quite low on the foot, and elongated, compared to
> the basal theropod condition.  The ball-like articulation of the
> phalanx in _Archaeopteryx_ and _Confuciusornis_ could have allowed the
> first toe to be swung medially - but certainly not posteriorly
> (plantarly).  However, if this condition was present in _Jeholornis_ ,
> and if the articulation or the shaft of the phalanx was modified, then
> it could have allowed a more posteromedial orientation for this digit.
>  But in the absence of hard anatomical data (not provided in the
> abstract) this is just pure speculation on my part.
>
>
>
>> 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.
>>
>>
>


Jason Brougham
Senior Principal Preparator
Department of Exhibition
American Museum of Natural History
81st Street at Central Park West
212 496 3544
jaseb@amnh.org