Re: Articles in Integrative Zoology

[Tim Williams <twilliams_alpha@hotmail.com>]

A response to an old message...

>    Integrative Zoology Volume 1 Page 4  - March 2006 
> doi:10.1111/j.1749-4877.2006.00004.x Volume 1 Issue 1 Feathered dinosaurs 
> from China and the evolution of major avian characters Xing XU


Although I don't have an actual copy of this article, I was able to read 
through a poor-quality reproduction and jot down a few things.  Much of the 
article is a synopsis of the bird-theropod link, with an emphasis on feather 
evolution.  Perhaps the most important new idea is Xu's hypothesis on the 
origin of the feather, which differs slightly from Prum's hypothesis...

Xu hypothesizes that the earliest feather homologue was a tubular filament 
("Stage I") that came *before* the feather follicle.  The tail filaments of 
_Psittacosaurus_ and the fuzz of pterosaurs represent this stage.  (No 
mention of _Longisquama_.)

"Stage II" feather homologues show distal branching, of the kind seen in 
_Dilong_, _Beipiaosaurus_ and certain feathers of _Sinornithosaurus_.

"Stage III" includes the feather follicle, the rachis, and the planar vane 
(although Stage III feathers need not show both a rachis and planar vane).  
Stage III is seen in certain feathers of _Protarchaeopteryx_, _Caudipteryx_, 
and _Sinornithosaurus_.

"Stage IV" is the stiff pennaceous feathers seen on the limbs and tails of 
_Protarchaeopteryx_, _Caudipteryx_, and _Microraptor_.

"Stage V" feathers are those in feather tracts (thus, pennaceous feathers 
are found elsewhere other than the limbs and tail).  The various specialized 
feathers seen in modern birds represent Stage V, even if they superficially 
represent earlier stages in their structural simplicity (e.g., natal down, 
filoplumes, etc).

On another (related) topic, Xu holds that the four-winged morphology 
exemplified by _Microraptor_ was ancestral to the two-winged morphology of 
birds, by secondary loss of the hindwings.  Also, _Microraptor_ is said to 
be able to orient its hindlimbs "subparallel" to the tail, so that the leg 
and tail feathers form a lift surface.  There is no in-depth discussion of 
the anatomical basis for this, except for a statement that "the posture is 
consistent with the osteological features of the pelvis and hindlimbs of 
eumaniraptorans".  An "arboreal pes" is posited to be primitive for 
Eumaniraptora.  (An "arboreal pes" in this context is different from a 
perching pes, though not much else is said on this matter.)

Cheers

Tim