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Genus differentiation
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by LongDucDong on March 3, 2006
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Perhaps some of you knowledgeable folks can answer this for me... What differentiates the genus Crotalus from Sistrurus? Anyone know?
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RE: Genus differentiation
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by canuck on March 3, 2006
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mainly the head scales differentiate the genus.
Sistrurus has only 9 head scales i think?
(No reference books handy as I write this note)
A good book by Lauwrence Klauber,Rattlesnakes, their life history. abridged addition at least has a comprehensive description of the differences.
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RE: Genus differentiation
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by Snake18 on March 3, 2006
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From what I know Sistrurus has large plates(like Agkistrodon) on its head while Crotalus only has very small scales.
Alex S.
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RE: Genus differentiation
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by Cro on March 3, 2006
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Steve: What the others have said about the difference between Sistrurus and Crotalus is generally correct.
Early classification put rattlesnakes with the 9 large head plates (scales) into the Genus Sistrurus.
The rattlesnakes in the Genus Crotalus had numerous small scales on the top of the head.
However, a problem cropped up with the Mexican Pygmy Rattlesnake. This is a relict form of rattlesnake that had charistics of both Sistrurus and Crotalus.
There are three subspecies of this snake: Crotalus r. ravus, Crotalus r. brunneus, and Crotalus r. exiguus.
Originally, this snake was called ``Sistrurus ravis,`` due to the 9 head plates.
The snake was re-classified and re-named ``Crotalus ravus,`` by James Murphy et al., in 2002.
Although ravus has the 9 large head scales of Sistrurus, its DNA more closly matches Crotalus.
You can read about the ongoing discussions on how to classify this snake in The Venomous Reptiles of the Western Hemisphere, Volume II, by Jonathan Campbell and William Lamar. See Pages 662 - 669, and 575 - 577.
So, if you are looking for the difference between American Sistrurus and Crotalus, the 9 head plates is the way to go. If you are looking at Mexico, things change.
Hope this helps. Best Regards JohnZ
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RE: Genus differentiation
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by LongDucDong on March 3, 2006
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Thank you very much gentleman! I appreciate the info that you guys offered, that helps clear up some questions I had. Here I was looking at a S. catenatus and a C. horridus and couldnt make out the difference. Of course head-scale detail was nil, but now that you guys mention that, I can definitely see the difference. Thanks once again! Take care.
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