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Re: Microraptor hanqingi, new species from China.
Jason Brougham <firstname.lastname@example.org> wrote:
> Tim has suggested that the differing leg proportions of modern birds and
> basal paravians make them poor analogs for one another.
> I investigated this possibility. In Bipedalism, Flight, and the Evolution of
> Theropod Locomotor Diversity. Stephen M. Gatesy, Kevin M. Middleton. Journal
> of Vertebrate Paleontology,
> Vol. 17, No. 2 (Jun. 19, 1997), pp. 308-329 the leg proportions of various
> theropods are measured and plotted out.
> First finding, Archaeopteryx does not group with cursors. It groups with
> Confuciusornis, Sinornis and Cathayornis. This cluster overlaps with
> Galliform birds (Fig 5 B). The nearest non
> avian - theropods are troodontids like Saurornithoides, Sinornithoides and
> oviraptorids like Avimimus.
> So, the empirical evidence indicates that galliform birds are definitely good
> analogs for basal avialans as far as leg proportions go.
Thanks for prompting me to re-read this paper, Jason. Yes, you are
right: the hindlimb proportions of _Archaeopteryx_ do cluster with
galliforms (Gatesy and Middleton, 1997).
However... in modern birds, the femur is largely decoupled from stride
generation. Thus, the distal hindlimb elements are often elongated to
compensate for this subhorizontal orientation of the femur, with
stride generation (the "effective"hindlimb) initiated at the knee, not
the hip-joint as in the primitive theropod condition. _Archaeopteryx_
appears to have retained to primitive theropod condition.
The aim of the Gatesy and Middleton paper was to highlight the
impressive locomotor diversity of birds, as attested by the huge
disparity in hindlimb proportions within the group. The same sector
of ternary morphospace occupied by _Archaeopteryx_ and galliforms also
includes some pigeons, trogons and birds of prey - so I would hesitate
to compare hindlimb proportions between modern birds and basal avians
as a way of identifying possible analogs for _Archaeopteryx_.