Re: Dinosaurs and birds

[Tim Williams <twilliams_alpha@hotmail.com>]

Scott Hartman wrote:

> That's a fantastic question Mickey, and we can't answer it as long as 
> people just assume that Archaeopteryx was volant and therefore all more 
> advanced birds must have been too. For example, dinosaur including 
> Archaeopteryx are abysmal in adaptation for climbing.

I think '"absymal" is an overstatement  There's enough modifications to the 
manus and/or pes in certain basal birds as well as microraptorans and 
_Pedopenna_ to suggest that these maniraptorans had at least some climbing 
ability.  I'm referring to characters such as elongation of the penultimate 
phalanges, distal migration of the first metatarsal, and shape of the 
unguals.  Sure, these guys probably couldn't perch, but they could have been 
scansorial - and ceratin characters appear to back this up.

> Now imagine that wing assisted incline running (WAIR) opened up arborreal 
> niches (because all of the biomechanical arguements against dinosaurs in 
> trees go out the window if you can walk up a trunk) for the first time, 
> leading to an explosion in arborreal but largely non-volant winged 
> theropods.

I like WAIR, and it has the benefit of experimental proof in modern birds.  
However, it was my impression that WAIR would not allow a primitive bird to 
actually "walk up a trunk".  Modern birds can employ WAIR to ascend trunks 
more than 5m high, but they have the full complement of flight abilities.  
The vertical component of WAIR in the first winged theropods would have been 
far more modest, wouldn't it?

> Did Sapeornis and Jeholornis fly?  Quite possibly, but shouldn't we perhaps 
> test between the above hypothesis and the prevaling assumption of volancy?

I don't think it's an "assumption" at all.  It's grounded in some pretty 
solid research.  And, at the end of the day, we are never going to <know> 
for sure what Archie's flight abilities were like.  We can advance 
hypotheses and test the viability of various aerodynamic models till the 
cows come home - but without a real-life Archaeopteryx, there's no way to 
draw a line under this.  Even aerodynamic models have their limitations, 
since they incorporate values for factors such as pectoral muscle mass, body 
weight, and dimensions of the wing that require a degree of educated 
guesswork.

All I'm saying is that AFAIK there is no evidence to <disprove> the notion 
that _Archaeopteryx_ (or _Jeholornis_ or _Sapeornis_) were capable of some 
form of powered flight.  Nor is there any compelling evidence to refute the 
phylogenetic hypotheses that all later birds (including modern birds) 
evolved from something that looked a lot like _Archaeopteryx_ (i.e., had the 
same or similar combination of characters states).  In other words, the 
flight abilities of _Archaeopteryx_ do not need to be <known> in order for 
this taxon to retain its primacy in hypotheses on the origin of avian 
flight.

> As other non-volant, winged maniraptorans show, there are a wide range of 
> things you can do with wings that don't require actual flight,

True.  But although there is a 'wide range' of things that birds use their 
wings for, most of them do use their wings for flight.  The wings of 
_Archaeopteryx_ most closely resemble the wings of modern flying birds more 
so than the wings of modern non-volant birds.  I'm referring not just to the 
overall 'shape' of the wing, but also the morphology of individual remiges.  
True, the skeletal morphology of Archie is strikingly different to that of 
modern birds, so I'm not going to push this too far.

Cheers

Tim

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