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Re: Emus a Model for Dinosaurs?
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
*** Agreed, makes sense in order to maintain balance according to
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.
*** Also the dentition does not conform to a typical predator, but as the
manual digits and unguals remain functional, rather than prey pursuit, maybe
they're employed in nest construction, manipulating eggs, or other foraging
dependent upon diet. As the feathers are not for flight ( perhaps instead
assisting in incubation, display, or cloaking shield from sunlight if it
seeks out small aquatic vertebrates / invertebrates ) they wouldn't require
the care and maintenance necessary in fliers. . .
_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.
*** That would be a consideration in an animal "well endowed", one could
assume a sizable array in something like Nomingia ( wonder how much a
peacock fan weighs?)
>>are any secondarily flightless theropods ( or those initially evolving
*** Makes me wonder how many failed evolutionary attempts were necessary
before they got it right and outperformed Arch.& Co. within that competitive
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.