Re: Dinosaurs and birds

[Dann Pigdon <dannj@alphalink.com.au>]

Anthony Docimo writes: 

> could maniraptors (not birds) with feathered arms  have had an advantage 
> over maniraptors lacking feathers on their arms, when it comes to those 
> turning manuvers and clearing obstacles?

Another advantage of 'winged' forelimbs in a fast runner would be to help 
streamline the folded forelimbs into the body wall to reduce drag. In this 
instance the 'wings' would be kept tightly folded while running. 

Many extant animals go through an arborial phase as juveniles, which they 
grow out of (Komodo monitors come to mind). I envisage the juveniles of some 
dromaeosaurs (like *Saurornithosaurus*) spending a lot of time in trees, 
avoiding larger predators and perhaps chasing small arborial prey. The 
recurved second toe would have made a handy grapple, while relatively large 
forelimb proportions and low body mass could even have made them semi-volant 
(or at least capable of parachuting in case of a fall). Upon reaching adult 
size, they could have switched to a more cursorial lifestyle, in which the 
forelimbs (and perhaps 'wing' fans) were too small for flight (or even 
gliding), and were perhaps used in the manner I suggested earlier (and as 
display and/or brooding devices). The recurved toe claws could have then 
functioned more as predatory tools than for climbing. 

The question would then be whether such behaviour resulted in some early 
maniraptor lineages becoming paedomorphic and retaining volancy their entire 
life (eventually becoming 'birds'), or whether such behaviour was a case of 
ontogeny recapitulating phylogeny (ie. flight being ancestral to 
dromaeosaurs, and being reflected in their juvenile stage). 

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Dann Pigdon
GIS / Archaeologist         http://www.geocities.com/dannsdinosaurs
Melbourne, Australia        http://heretichides.soffiles.com
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