Simon, what is your take on reptiles though and what degree of feeling > pain do they feel? Asking as they're cold blooded also, but are their brains any larger or just a simple as a fish's?
That's a complicated question in some ways Jeff.
Snakes are, in general, quite "simple" and don't seem to have much learning behaviour regarding threatening circumstances other than staying still, moving away, or exhibiting their own threats.
They are well known for wrapping around heat bulbs and burning themselves to the third degree. This would show that "pain" doesn't register (as we've been discussing re. fish) in a way that we mammals recognise.
Some lizards have more developed brains and show some "cognisant" behaviour. Monitor lizards, for example.
But again, they can suffer what we would term a "painful" injury and show no outward signs of pain.
I remember one of my Green Tree Monitors jumping and flinging herself around the cage with complete abandon, chasing insects and so on, absolutely normal behaviour, all the while she had a broken rib and an abscess on top of it.
Also, many lizards (and the odd snake) can drop their tails from any point along the length of it, which self-seals to prevent blood loss and infection. Then they re-grow it. Salamanders can re-grow complete limbs.
This would seem to preclude sophisticated pain receptors such as are present in mammals.
I don't believe reptiles/amphibians feel "pain" as we know it, either.
