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Re: AW: Heterodontosaurid with protofeathers



Quoting Amtoine Grant <rascienz@shaw.ca>:

> They also COULD be venemous,  
> something we'll probably never know for sure. YOU WOULD think that a  
> group of warmer-than-usual-blooded reptiles that diversified so much  
> over approx. 140 million years would produce at least a FEW poisonous  
> species.

"Poisonous' and 'venomous' are two different things. As I understand it, vemon 
is usually only toxic 
when it enters the blood stream, while poison can kill by being injested. 
That's why you can drink 
snake venom, and your digestive juices will break it down harmlessly (hence why 
snakes can eat 
animals they've envenomated). Having an open wound in your mouth, throat or 
stomach may 
make it a dangerous practice though.

There are a few species of poisonous extant birds, but no venomous ones. In 
contrast, there are 
only two venomous mammals that I can think of (the platypus and Solenodon), but 
I'm not sure 
there are any poisonous mammals.

It's much easier for an animal to evolve to be poisonous to some degree than to 
be specifically 
venomous. Venom not only requires a toxin, but also an injection system. Venom 
is usually 
injected via a deliberate act (biting, or pricking with a spur), which requires 
behavioural changes as 
well as the complex structural relationship between venom gland and delivery 
system.

Poison however can be accumulated from eating toxic food (poison arrow frogs, 
and probably the 
poisonous birds) or by exuding toxins from glands in the skin (cane toads). 
Most poisons are a 
passive defense that prevents the animal from being eaten. There is certainly 
no poisonous 
predator that I know of that deliberately throws itself into the mouths of it's 
intended prey!

-- 
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Dann Pigdon
GIS / Archaeologist              http://geo_cities.com/dannsdinosaurs
Melbourne, Australia             http://heretichides.soffiles.com
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