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Franziska Norman, Gallery Volunteer
Sedgwick Museum of Earth Sciences

I love the ammonite Australiceras gigas from the Cretaceous period.

Its strange, almost absurd, shape looks as if it had been invented for the sheer fun of it. The shell grew at first as any normal ammonite shell would, in a tightly coiled spiral, but then, as the animal grew older, the shell grew in a straight line for a while, before starting to coil back upon itself, so the animal spent the rest of its life permanently looking at its own rear end.

Ammonites had already been around since the Triassic period, always sticking to the same tightly coiled shape, looking in life probably much like their distant cousin, the living nautilus. And like the nautilus, many of them probably moved by jet propulsion, propelling themselves through the water in permanent reverse gear, occasionally bumping into things because they couldn’t see where they were going.

But then, during the Cretaceous, they suddenly exploded into a multitude of crazy shapes, some coiling themselves into little towers, seemingly mimicking the shells of marine snails, some developing straight shells like squid. And then there was Australiceras, in my opinion the craziest shape of them all.

According to the principles of evolution, somehow these new shapes must have given the ammonites an advantage in the struggle for survival; maybe they were now able to live in places in the sea that had so far been inaccessible to them; maybe they were able to find food in new ways.

But what advantage, I wonder, could a shape like Australiceras’ give to an animal, whose rear end must surely have eventually got in the way of its mouth?

We may never know for sure. In my most absurd moments, I think maybe these creatures just existed so that we could, millions of years later, look at their fossils and smile. Maybe Nature does have a sense of humour...