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Re: Emus a Model for Dinosaurs?



Thanks Tim,

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 developmental structure.
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
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.
*** Makes me wonder how many failed evolutionary attempts were necessary before they got it right and outperformed Arch.& Co. within that competitive niche.


Cheers,

Mike S.