Giant penguins weighing up to 150 kilograms once roamed the waters around New Zealand. Claire Concannon speaks to a palaeontologist and learns about penguin evolution, extinct species that dwarfed today's emperors, and why Aotearoa is such a great place to study these birds that 'fly' through the water.

Evolution spins out some crazy designs.

Bats that can hunt in the dark using echolocation, spiders that use water surface tension to detect prey, and rugby-ball-shaped birds who look like they are wearing formal attire as they dive through the water to hunt.

Marching penguins, dancing penguins, surfing penguins. These birds have found their niche in both the oceans, and on our movie screens.

What made penguins the beloved birds that they are today?

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From flying in air, to flying in water

Our story begins 62 million years ago. "I recognise that that's just a number," says Dr Daniel Thomas, of Massey University. "But to put that into context - at 66 million years, that is when the non-avian dinosaurs disappeared from the planet."

Once a dinosaur-obsessed kid, Daniel continues to follow his passion, now with a focus on one of the descendants of avian dinosaurs. He studies penguin fossils and their evolution across time.

The earliest penguin fossils come from right here in Aotearoa, from North Canterbury. Dated to a mere four million years after the dinosaur extinction event - a blink of the eye in geological time - these bones indicate that early proto-penguins had already committed to life in water, although they may not have been very efficient divers.

Birds that fly in the air - like the once-ancestor of the penguin - have hollow bones. But these early fossil bones found in Canterbury are dense, better suited to diving under water.

Across the next 6-13 million years, the wings of these birds underwent significant changes. No longer were they able to tuck back in after a stroke, instead the joints would stiffen so that they effectively became fixed paddles, driven by the shoulder.

The time of the giants

Penguin evolution is constrained by many factors: the difficulty of 'flying' in dense viscous water, the issue of constant heat loss, the need to also go on land to breed. But that didn't stop evolution from testing all the penguin size and shape possibilities within these constraints. And early on in penguin evolution, something interesting happened - penguins get very large. …

Go to this episode on rnz.co.nz for more details