This is

is Scientific American 60 Second Science.

I'm Christopher Intagyata.

Freshwater Dolphins live in many of the world's biggest rivers,

from the Amazon to the Ganges,

and they differ in a lot of ways from their better known ocean-going cousins.

They have a flexible neck, they have different types of teeth.

They can also move their flippers independently in different directions so they can turn backwards.

Gabriel Melo Santos, a marine biologist at the University of St Andrews in Scotland.

When I decided that I'm going to be a biologist, he just decided that I want to study dolphins.

And being born in the Amazon, it was only natural to go for the river dolphins.

He says another thing that sets his study subjects apart from marine dolphins are their calls.

Over several years Melosantos has recorded the sounds of Araguan river dolphins

that came calling at the Mocha juba Fish Market, that's on Brazil's

Tocantines River. Then using Sound Analysis software his team fished 237

distinct sound types from the recordings, indicating the dolphins have a wide repertoire.

The call collection published in the journal Pier J has only a few whistles.

Instead, three quarters of the collected sounds were short two parters like this one,

produced by a female calf as she rubbed her head on her mother's belly.

It's a call that's more similar in structure to the ones

Orca's and pilot whales make to identify a family or social group

then to the social whistles of marine dolphins.

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