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RE: Ratite phylogeny

Is it possible that the different trajectories of the wings in different species of flightless birds is related to function? For example, the ostrich shows extended growth of its wing, because adult ostriches actually use their wings for something (display, thermoregulation, etc). Ditto for tinamous, which still fly (although not well). On the other hand (so to speak), the wings of emus are vestigial, so the forelimbs have a slower rate of growth as embryos.


So, what do we do  with this?  From the North American Paleontological
Convention 2001.

 MARSHALL, Cynthia L., Museum of the Rockies, Montana State University,
Bozeman, MT, USA

One basal flight loss event is the most parsimonious explanation for
flightlessness in the ratite clade. Therefore, if flight were lost only
once in this group, a similar pattern of wing reduction would be
predicted for ostriches and emus.

A series of ostrich, emu, tinamou, and chicken embryos were obtained and
the growth patterns of the wings compared. The chickens and tinamous
served as outgroups for phylogenetic pattern analysis. Wings of the
ostrich, chicken, and tinamou embryos grew at similar rates. The wings of
the ostrich embryos grew for a greater length of time, resulting in a
longer wing. The emu embryo wings grew at a slower rate, resulting in a
vestigial wing. The emu wing growth is slowed in comparison to the
ancestral condition, demonstrating a pattern of paedomorphosis. In
contrast, the ostrich embryo extends growth at the ancestral growth rate,
demonstrating a pattern of peramorphosis. I propose that the
emu/cassowary clade shares a small, non-flying ancestor that subsequently
grew large, whereas the proto-ostrich was a flying bird until becoming
too large to sustain flight capacity. Fundamentally different wing growth
patterns in ostriches and emus supports both multiple flight loss events
and separate mechanisms leading to flight loss within this clade.

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