I have just seen the BBC film Voices of the Deep, which is part of the BBC Ocean Giants series currently available on I-player. and the shoot of, for example, the different ways in which individual pods of orcas (killer whales) catch their prey clearly shows a high degree of culture. Other recent items I have seen on line include research into Dolphin language and the following video on Youtube which showed how orcas could disable and kill the Great White Shark
If we think about the great apes and the fact that humans developed language perhaps we should not be surprised if it turns out that marine mammals such as dolphins and orcas also have language - perhaps millions of years older than our own.
For land mammals such as early hominids there are definite costs of having a large an active brain. Brains are energy hungry compared with most other organs so a bigger brain means more food needs to be eaten. For animals living in the tropics excess energy has to be lost to prevent overheating. There is also the greater weight of a larger brain, which needs to be packaged in a robust (and heavy) skull.
For large marine mammals the costs of having a large brain are comparatively very small. They live in water that is routinely significantly lower than tropical daytime temperatures so a busy brain can be considered as a heat source to help maintain body temperature.The density of the brain is similar to that of water so there is no extra weight of brain to carry around, and the shape and lifestyle of the animal means that accidental damage is far less likely. In addition the environment limits the use of eyes for sophisticated visual social interaction .- and sound is the obvious substitute.
I am watching for further developments with interest, as if it turns out that we have failed to recognize the languages of other intelligent life forms on earth what hope is there of recognizing alien life in the SETI program.