Ben,
Actually, Python and Morelia are sister taxa, so neither is more derived than the other. At least the last time I checked the literature (phylogeny below), so unless anyone has done a big python phylogeny lately that I didn't hear about, they would be the same. The data show that the latest divergence in pythons led to both the genera Python and Morelia, so you can't really say either is more derived than the other because they came from the same ancestor. Does that make sense? Once either of them becomes multiple genera, then you could say that one would be more derived, but until then they would be equal. I hope that is making sense
And all this is according to what is known right now, but further research could very well show that we have been incorrect, although with Aspidites having some "venom glands" I think that would be further evidence that Aspidites is for sure the most basal...but who knows if Python and Morelia are really the most derived. Time will tell. And if anyone does have a more recent python phylogeny I would love to see it. I haven't poked around the literature for a few months, so something could have come up, but this one by Kluge is the one that most people go by that I know of.

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Ben
www.australianaddiction.com