poisonous animals

Does anyone know when the first organisms appeared that were using poison to either defend them selves or to attack other organisms? Is there any change in anatomy that can show when this happens.

Terog, Organisms have been using antibiotics against each other for billions of years (long before there were eukaryotes, multicellular or unicellular), probably beginning very soon after the evolution of life itself. Animal poisons are 'antibiotics' (in the broad sense of the word), often injected by stingers or fangs (which can be seen morphologically). However, sometimes these poisons are secreted by the skin or other tissues that would not be readily apparent in the macroscopic anatomy of the animal (or plant). Amphibians are a good example.

Ken wrote-

Now as for dinosaurs, there was the SVP 2000 that reported the Mexican theropod tooth that may have been used for funneling poison. And correct me if I am wrong, but isn't there a bird that emits toxins that cause predators to want to spit it out?

-Nick Gardner-

One of the first was blue-green algae, which used oxygen to poison other organisms. Eventually enough oxygen escaped that it poisoned the entire atmosphere, and most organisms had to adapt to living in a poisonous oxygen soup.

The surviving anaerobes provide a brilliant panoply of toxins, so it is likely that algae weren't the first poisonous organisms by any means.

Modern cephalopods trend to be venemous. They posess cephalotoxins which is a combination vasopressor, cardioinhibitor, and neurotoxin (in varying amounts). Consider that the venom of the blue ringrd octopus is considered to be one of the 5 most deadly substances on the planet....

This kind of toxin is probably as old as cephalopods themselves and likely dates to the earliest cambrian at the very least.

Glen Garnder