Re: paleonet Origin of birds

[patricio@xxxxxxxxxx]

Dear Paleoneters,

I have been away for a couple of weeks and I haven't been able to follow the complete discussion on origin of birds. 

What call my attention is a misconception on the nature of the cladistic studies. A cladogram show us the way in which evolution runs.  For example, with a cladograma in front of us, we are able to trace the evolution of feathers from simple cover filaments (¡°fuzzyraptor¡±) or quill-like structures (Psittacosaurus, by the way an ornithischian!) to asymmetric feathers in wings adapted to active flight. Of course, there are a lot of gaps but a cladogram help us to fill the gaps. However, as in the tube, "Mind the gap". A cladogram, as any other scientific hypothesis, should be revised.
 
The wings of Archaeopteryx are covered with asymmetric feathers. This type of feathers is adapted to active flight. However, a lot have been discussed on the flight abilities of Archaeopteryx. In my point of view, mainly because of a very high estimation of its weight (Archie has hollow bones, and aerial sacs should invade also other pars of the body)
 
Some moths ago, Angela Milner, Tim Rowe, I and others colleagues contributed to the comprehension of origins of flight with a recent study by micro-CT and computerized 3D of the braincase of Archaeopteryx showing that it was more bird-like than we thought.
 
Dom¨ªnguez Alonso, P.;Milner, A.C.; Ketcham, R.A.; Cookson, M.J. & Rowe, T. (2004) The avian nature of the brain and inner ear of Archaeopteryx. Nature, 430: 666-669
 
We have proved that Archaeopteryx could fly. Moreover, our point of view is that Archaeopteryx had an active flight being able to perform a delicate flight control. 
 
Archaeopteryx had enlarged brain regions for vision (mesencephalon, allowing more visual input and ¡°automatic¡± output to muscles and other regions of the brain) and movement control (an enlarged cerebellum, mesencephalon) associated with a big telencephalon (general coordination). 
 
Archaeopteryx had the brain of a bird, not the brain of a dinosaur (including those close-related to birds such as Oviraptors); moreover, the ratio volume of brain / [estimated] body mass is more bird-like than previously estimated.
 
In addition, the inner ear also resembled that of modern birds. The semicircular canals are placed in the three navigation planes, vertical-longitudinal, vertical-transversal and horizontal (for accurate control of pitch, yaw and roll). That control is not clear in land-reptiles (including most of archaeosaurs) where semicircular canals form a tetrahedron-like structure making difficult the discrimination of roll and pitch movements. 
 
Archie had the hardware to flight, we show that also had the software.  The question now is what the brain and ear are like in the most bird-like dinosaurs
 
 
All the best,
 
Patricio Dom¨ªnguez