Elephants’ trunks are muscular hydrostats, which means they are made up of mostly muscle and have no bones or joints. An elephant’s trunk has over 40,000 muscles, which is much more than the entire human body:

This means that although trunks don’t fossilise, other evidence can help researchers determine that elephants had trunks. For example, researchers can study the structure of an elephant’s skull to infer that it had a trunk. Moreover, we have mammoth mummies with their trunks intact:

Scientists now believe that elephants’ trunks evolved from a snorkel-like structure that helped their semi-aquatic ancestors move underwater:

Eventually, the trunk became longer and more versatile, and evolved into the elephant’s trunk we see today.
We do not know what the dinosaurs looked like or how they acted. All we have to go on is there bones and occasionally a footprint or skin print, even the bones can be questionable as fragmants are found with little context on where they go. Scientists can only speculate, linking what they find to modurn creatures, hypothising what the creature was when it was alive.
But modern creatures it is a little different. We have so much literature, pictures, paintings statues and even the aural tradition. These well known and popular creatures could become extent but there is so much evidence of what they were even as they pass into legend.
A lot more than just the elephants would need to be lost before anyone would question what these bones. If all of that went and future humans, some sort of alien or what ever comes next after us comes along in 10,000 plus years and finds a fossil of an elephant and tasks themselves about learning about this creature then there is a chance they will not consider the animal had a trunk.
Maybe they would conclude something like this artist sketched up.
