Re: How did Salmonella evolve?

An interesting question Justin, that I will answer in 2 parts.

The 1st part is, are things the same today as they were in the past? We 
always look at evolution and realise that reptiles evolved from 
amphibians, that birds came from reptile's etc., but rarely do we think 
about bacteria in the same way. Let us think of the Dinosaurs you mention 
in your question. Are they here today? No that’s obvious, they all died. 
But we never consider bacteria. So are all the bacteria from that time 
also dead and therefore are the bacteria present today different from the 
ones then. Well again lets consider the Dinosaurs. There are 
surviving "Dinosaurs", the crocodiles and alligators. So there may be 
surviving bacteria. Without a time machine this is tough call. If there 
are bacteria today that were present then, they will have changed overtime 
but may be similar.

To be more to the point on your question, is Salmonella the same today as 
it was then? Well Salmonella is predominantly found in the guts of 2 
groups of organisms Mammals and Birds, neither of whom were hear in the 
past. Why do they like this environment? Well its warm and they like to 
grow at that temperature. Were the guts of dinosaurs warm? Well maybe. So 
we can't really say that Salmonella lived in the guts of Dinosaurs.

To conclude organisms today are not like they were in the past, time does 
not freeze. Therefore bacteria today are probably not the same as in the 
past. All organisms adapt to live somewhere, Salmonella is the guts of 
warm organisms and the guts of dinosaurs may not have been that warm.

So my gut feeling without the precise data, is that Salmonella is a 
relatively new organism, much older than we are (humans) but maybe not as 
old are as the Dinosaurs are. It probably appeared when warm-blooded 
organism became prevalent. So, no Salmonella did not infect Dinosaurs but 
other similar organisms probably did.