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Re: RE: more cladistics



>>I was simply
>>saying that the derived character "feathers present" is and will remain =
>a
>>very weak synapomorphy of Avialae, because it is so rarely observed.  =
>>Other
>>derived, skeletal characters (see Gauthier, 1986, for the classic work) =
>>unite
>>Archaeopteryx and modern birds.
>
>What skeletal features unite Archaeopteryx and birds? As I understand =
>there are a lot of features which are more theropod then bird.

There are many features which demonstrate that Archie (and other birds) lie
among the Theropoda.  Additional evidence unites Archie with later birds.  I
will bring my copy of Gauthier to the comp lab this afternoon, and post these.

(Note that Archie is VERY primitive, so it is very much like the nonavian
theropods.  However, the additional derived characters link it to other
birds.  This is the same with birds, crocs, and lizards: while crocs and
lizards seem similar, and share many primitive traits, various derived
characters show a more recent common ancestor of crocs and birds than with
crocs and lizards.)
>
>I would also like to know what people think on the evolution of birds. =
>For example, did they evolve "ground upwards" or "trees downwards", as =
>David Norman puts it? Was Archaeopteryx a tree dweller? If so were other =
>dinosaurs?

As someone working on theropod lifestyles, I'd like to point out at
arboreality and cursoriality are NOT mutally exclusive habits.  I think the
weight of evidence shows that Archie (and possibly other small theropods)
were scansorial: animals which spend much of their time (including food
procurment) on the ground, but occasionally going into the trees (to escape
predators, for example).  In the modern world, the cats (great and small) make
good examples of scansorial predators.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
College Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661
Phone:301-405-4084