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Re: Emus a Model for Dinosaurs?
Michael Skrepnick wrote:
of particular interest is their assertion that center of gravity remains
the same in Caudipteryx as in
all other non-avian theropods and if so negates the necessity of a shift in
hindlimb locomotion from the hip to the knee. . [snip] If the reduction in
caudals was not enough to affect hindlimb movement in Caudipteryx itself,
The neornithean "body plan" (at least where volant forms are concerned) is
characterized not only by a shortened tail, but also by a larger head,
longer forelimbs, and expanded pectoral musculature +skeleton. All these
features conspire to drag the CM well forward of the hips. These features
have been reversed somewhat in ratites and other flightless cursorial birds
- except for the tail, which remains short. Ratites do show a caudal
lengthening of the pelvis though.
As for _Caudipteryx_, it has rather short forelimbs by coelurosaurian
standards. Also, I wonder how useful its forelimbs were, given that they
were: (a) covered in feathers; (b) useless for flight; (c) functionally
didactyl. I really don't think the forelimbs were used to catch prey. This
speaks to a reduced pectoral musculature compared to other maniraptorans
(avian and non-avian). So the shorter tail may be correlated with a less
weighty shoulder+forelimb region. Just an idea.
I wonder if there is any impact in oviraptorosaurs like Nomingia having
further reduced caudal series / pygostyles. . .
_Nomingia_'s tail was certainly short (24 vertebrae), but it was also looks
quite 'hefty': big, flaring chevrons; median dorsal crest (made up of pre- +
postzygapophyses) running down the last third of the tail; and the
blade-like pygostyle. If the tail was feathered, the rectricial frond or
fan would added extra weight too.
are any secondarily flightless theropods ( or those initially evolving
flight ) subject to a shift in hindlimb locomotion, or is this strictly
relegated to neornithes / advanced birds?
Excellent question. This requires more study. It's unclear how or when
this shift occurred in avian evolution, but it was certainly
post-_Archaeopteryx_, and probably close to the base of the Pygostylia
(Confuciusornithidae and higher), not surprisingly.
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