What are the key dates for the development of operant conditioning? I am trying to build up a timeline of the development of operant conditioning. So far I have the following


$1898$ - Thorndike performs experiments using his puzzle box of which Skinner based his work on.
$1930$ - Skinner invents a similiar box called the "Skinner box" while studying as a graduate student.
$1938$ - Skinner coins the term "operant conditioning".
$1947$ - Skinner performs experiments on pigeons.
$1948$ - Skinner performs experiments on rats. 


However, this timeline leaves me skeptical for two reasons. 

The first is that the timeline is very stretched out. Skinner invented the box and then it took him 17-18 years to publish his famous studies. What experiments was he performing with his box that weren't as groundbreaking in all those years when his groundbreaking results features a very basic setup?

The second is that Skinner apparently swapped from rats to pigeons in his experiments because they lived longer, learnt faster and were easier to handle yet the according to my timeline the rats experiment took place after the pigeon one (or perhaps not and he just published them in that order).

I suspect my timeline is not quite right (afterall my references are random internet links). My question is what are the (correct) key dates of the development of operant conditioning? Key dates being the events I have highlighted above and any others you think I have missed. I had more references but unfortunately I can only post 2 links due to my reputation.
It would have been pretty strange for there to be multi-year gaps in Skinner's publication record, and in fact, Skinner continued to publish every year in both of those periods and beyond (Epstein, 1977). I've provided a link to a list of his publications which includes both periods, but there is no real way to say which of these publications were the 'key' studies for operant conditioning. Hopefully, this will still be of some help.

References


Epstein, R. (1977). A listing of the published works of BF Skinner, with notes and comments. Behaviorism, 99-110.