For the first time, researchers have recorded two Black Sea bottlenose dolphins having a 'conversation' with each other, and their communication appears to be far more sophisticated than we thought.

While scientists have known for years that dolphins use a very complex language to communicate amongst themselves, the new findings suggest that they might be able to string together five-word sentences, and could even use a form of 'grammar' to influence meaning.

"Essentially, this exchange resembles a conversation between two people," team leader Vyacheslav Ryabov, from the Karadag Nature Reserve in Feodosiya, Russia, told Sarah Knapton at The Telegraph.

"Each pulse that is produced by dolphins is different from another by its appearance in the time domain and by the set of spectral components in the frequency domain."

The team discovered these speech patterns using a new type of waterproof microphone called a hydrophone. This allowed them to record two dolphins at the reserve - named Yasha and Yana - with a high level of detail.

After analysing these recordings, the team says they've found evidence that the dolphins were forming 'words', by emitting different pulses that varied in frequency, volume level, and spectrum, just like human language.

While it's impossible to know at this stage what these words could mean, the team says the dolphins appeared to be forming sentences up to five words in length during their brief conversation.

There's even evidence of grammatical structures in place too, which would allow for more complex sentences, but more evidence is needed to confirm this. 

What's perhaps most fascinating about the interaction is that the dolphins appeared to be keenly interested in what the other had to say, and understood that they had to take turns vocalising to get their meaning across.

"The analysis of numerous pulses registered in our experiments showed that the dolphins took turns in producing [sentences], and did not interrupt each other, which gives reason to believe that each of the dolphins listened to the other's pulses before producing its own," Ryabov told The Telegraph.

"This language exhibits all the design features present in the human spoken language, this indicates a high level of intelligence and consciousness in dolphins, and their language can be ostensibly considered a highly developed spoken language, akin to the human language."

Based on these findings, Ryabov says there's enough evidence to suggest that dolphins do, indeed, have their very own language that we're only just beginning to understand.

The next step - and it's a big one - will be to figure out how to translate their 'words' into a human language.

"Humans must take the first step to establish relationships with the first intelligent inhabitants of the planet Earth by creating devices capable of overcoming the barriers that stand in the way of using languages and in the way of communications between dolphins and people," Ryabov said.

Speech might not be the only thing humans and dolphins have in common. Back in 2011, researchers found that dolphins value friendships and close relatives just like we do.

And earlier this year, scientists from Italy found that dolphins (and whales) mourn their dead.

It's going to take a whole lot more research to get us to a place where we can understand much of anything that dolphins are saying to each other, but being able to identity the key constituents of their speech patterns is a pretty great jumping-off point.

The findings were published in Physics and Mathematics.