|I would suggest that the premise may be flawed. Many "lower animals" do engage in trade. Packrats, for example, are notorious about leaving something behind to "pay for" what they take. Allegedly, in at least one lucky case that I recall - but not the source, this meant acquiring a whole bunch of gold nuggets in enchange for some stored grain or other food.|
When I was studying the local crows and providing little food items for them during work breaks, right at the start, one of the local family followed me to where it was able to drop a shiny screw right at my feet. It waited, apparently to see if I accepted the offering, and then flew off when I picked it up.
Some birds, such as ravens, expect you to give them some kind of present on first introduction. It you don't, the bird will ignore you. If it likes the present and accepts it, then you are granted "friend" status.
It occurred to me once that if I could train a bunch of crows, using a skinnner box to recognize specific items as being desireable in exchange for food treats, then I could have a flock of crows who would train their young to do the same, and I could expect a steady supply of coins and rings delivered back to me. Crows have amazingly good image memories, so it is certainly within the realm of possibility. Noone would likely notice all this going on, as the crows would be just doing their usual thing - at least until someone spotted crows stealing the tips at an outdoor cafe'...
However, someone told me recently that someone else was already doing this, stupidly advertising it, as well. So, I wonder how many crow retrievers are quietly competing for crow employees at this point? Clearly the crows will quickly learn to deliver to the site that gives the best food reward.
And then there are cats who bring their sometimes still-squirming prey back home to present to their owners. Despite their adament denials, cats can be trained. So, one counter that could be developed would be to train cats to hide within pouncing distance of a coin.
Given my limited knowledge, by extension I would guess that there are a host of more sophisticated transactions among pre-sentient animals.