Re: synapomorphies

[Adam Yates <zooamy@zoo.latrobe.edu.au>]

On Mon, 12 Feb 1996 Dinogeorge@aol.com wrote:



> 
> If all your characters line up nicely, then a cladogram is pretty obvious and
> your analysis is easy. But it rarely works out that way. For example,
> hyposphene-hypantrum articulations between the vertebrae characterize certain
> large theropods and sauropods. Is this a synapomorphy uniting the two groups?
> Some have used this feature in the past to support a monophyletic group
> Saurischia, uniting theropods and sauropods. But we now know that such
> intervertebral articulations relate more to the ability of the spine to bear
> weight, and that they arose twice independently: once in big theropods, once
> in sauropods. How do we know this? By analyzing suites of other characters
> that collectively outweigh this particular character and support other
> phylogenies.
> 

I don't know the distribution of this character. Are hyposphenes-hypantra 
found in the early small members of each clade? (ie. Coelophysis and 
Thecodontosaurus, respectively). As for the 
suites of other characters not supporting Saurischia, I know only one, 
that supports  the Phytodinosauria (that being broad, leaf shaped teeth).

Adam Yates