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Posted by chris_harper2 on May 11, 2003 at 09:20:36:
In Reply to: Clarification posted by patricia sherman on May 11, 2003 at 05:09:31:
::The Pantherophis are certainly proven to be incompatible with the Old World genera.
Like I said earlier, this is almost certainly true, but has not been "proven". At least not in any scientific manner.
Would I bet on it? Yes. Has it been proven? No.
::One of the most notable differences between them, is that many or all Old World rats have a Duvernoy's gland, and that organ is absent in all New World rats (and related New World genera).
Certainly a significant difference, but keep in mind the Duvenroy gland is ancestral to the clade you are referring too.
Moreover, there has been interbreeding among snakes that don't share other homoplasic characters (which the Duvenroy's gland is). Regardless, an accessory salivary gland should have no bearing on reproductive ability.
:Another thing that I suspect would prevent such hybridization, is a discrepancy between the diploid chromosome numbers of animals from the different genera.
This would make sense but has not affected other animals from hybridizing.
The old world Elaphe and the New World Clade are clearly distantly related. However, attempts to objectively measure that distance and apply criteria to determine at which point species are incompatible is not something we can predict. Otherwise, the scientific literature would not be full of some many papers speculating as to how these phenomena occur.
You and I are probably a lot closer on this than you realize. I just found the lack of passivity in your post to be misleading.