Re: Emus a Model for Dinosaurs?

[Michael Skrepnick <palaeopaint@dinosaursinart.com>]

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.