The scientists suggested that dolphins could be the only non-human mammals to indulge in elite societies.
Wild bottlenose dolphins bond over their use of tools, with distinct cliques and classes forming over decades as a result of their skills, scientists found.
The communities, which have been compared with societies such as the Bullingdon Club in humans, mean the aquatic animals share their knowledge only with those in their own circle, passing it down the family line.
Observing wild dolphins in Shark Bay, Australia, researchers from Georgetown University used hunting tools as a marker of dolphin societal habits.
Noticing some dolphins in the area used a sponge to protect their beaks while hunting, they attempted to discover why the practice had not spread.
They found the useful tool had first been used by a single dolphin nicknamed "Sponging Eve", after she scraped her nose while foraging for food in rough sand, the Daily Telegraph reported.
To solve the problem, she broke off a piece of sea sponge to protect her, going on to teach the behaviour to her offspring.
But two decades later, knowledge of the tool had not spread among the whole dolphin population in the area.
Scientists observed 36 spongers and 69 non-spongers in the area over a 22 year period, taking careful note of their relationships.
"Spongers were more cliquish, had more sponger associates and stronger bonds with each other than with non-spongers," they found.
The findings mean the traits of "inclusive inheritability" and culture are no longer considered exclusive to human beings.
"Like humans who preferentially associate with others who share their subculture, tool-using dolphins prefer others like themselves, strongly suggesting that sponge tool-use is a cultural behaviour," the scientists said.
This tendency to associate with those most like themselves is, scientists believe, a "critical role in human (sub)cultures", and "may be true for dolphin society as well".
