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Re: Venom in Sinornithosaurus



--- On Fri, 12/25/09, Mike Habib <habib@jhmi.edu> wrote:

>> On Dec 25, 2009, at 4:45 PM, don
>> ohmes wrote:

>> The picture I am getting, especially from Pinsdorf's
>> post, is that of a "large group of snakes" that seems to range
>> (among species) from mere incipient venom production (minus
>> any delivery system) to more highly evolved delivery systems
>> and more complicated toxins. In other words, each
>> representing various stages of a common process, perhaps
>> post-diversification morphological convergences overlying a
>> common ancestral ability to produce a specific type of
>> venom. Co-existing "transitional species" as it were.

> That is, more or less, one of the primary interpretations
> in the literature.  There is a competing hypothesis
> (and I don't have the time to check the citations right now,
> being Xmas day and all, but will pull the refs later) that
> solenoglyphs (front-moveable fangs) come from a proteroglyph
> ancestry (front fixed fangs), but that rear-fanged origins
> are all separate - that is, that those snakes with front
> fangs do not have a rear-fanged ancestry.  

I should point out that the "large group of snakes" referred to in the 1st 
paragraph (now emphasized by quotation marks) is the colubrids, not venomous 
snakes as a whole. Sorry about the unclear language. This limitation also 
includes comments about "common ancestral abilities", "being unfinished" (as 
opposed to the venom delivery systems in vipers or cobras) and "basal prey" 
(i.e., 'basal to colubrids'). 

Perhaps 'under construction' would have been a better metaphor than 
"unfinished", anyway. Apparently, I am in the camp of the "competing 
hypothesis" you refer to, although the apparent status of Colubridae as a 
"waste-bin" muddles this nice picture significantly. Whatever. It is just a 
picture, but one I was unaware of, and it makes this side-thread unusually 
worth-while. Thanks, and I will keep an eye peeled for further developments, 
especially the relationships between the various 'sort of' venomous snakes. 
Like garter snakes. Sheesh. Who knew?

To sum, and bring back on-topic: 
1) the logical premise that venom systems in vertebrates are more likely to 
arise in slow predators than in fast* predators seems at the moment to be 
criticism-free, although perhaps not unassailable. 
2) the observation that there are no extant fast vertebrate predators that 
utilize venom as a predatory device seems to be valid, so far. There are lots 
of examples on the slow side, including a large group of (the colubrids) that 
appear to currently 'under construction', when viewed as a whole.
3) one might speculate that carnivorous theropods were somewhat unlikely (but 
certainly not impossible) to evolve venom systems, making claims of evidence to 
the contrary that much more extraordinary...

*Defining the category "fast" as beginning near the speed at which a wild 
turkey can run (and meaning no disrespect to the faster snakes).