Researchers in the US have found that dolphins can remember the distinctive whistle of another dolphin they haven't seen in two decades, the BBC reported.
The authors believe that these long-term memories are a product of the complex social connections that dolphins have evolved.
In the study, the scientists used information on the relationships between 56 captive bottlenose dolphins that have been moved for breeding purposes between six different zoos and aquariums in the US and Bermuda.
The records, dating back decades, showed which of the dolphins had been housed together.
The researchers then played recordings to the dolphins on underwater speakers of the signature whistles of animals they had once lived with, and measured their responses.
Dr Jason Bruck from the University of Chicago who carried out the study said that when they are familiar with the call, the dolphins are more likely to approach the speakers for longer periods of time, however if they are unfamiliar with the call they are more likely to ignore the sound.
The researchers believe that the complex nature of dolphin social systems is behind the long term memory effect.
According to the researchers, a dolphin's abilities to recall events indicate that the cetaceans have a level of cognitive sophistication comparable to humans, chimpanzees and elephants.
While elephants are also reputed to have extremely long memories of up to 20 years, there is little scientific evidence of their abilities outside of family relationships.
The research is published in the Proceedings of the Royal Society B.
--ANI (Posted on 07-08-2013)