Tales of Jet-propelled Predators

11 December, 2011

The fossil cephalopod slab in Melbourne Museum’s Discovery Centre
The fossil cephalopod slab in Melbourne Museum’s Discovery Centre
Image: Nicole Kearney
Source: Museum Victoria

Question: What are the amazing fossils on the slab of rock in the Melbourne Museum Discovery Centre?

Answer: Although visitors have voiced some interesting interpretations of the large slab of rock in the Discovery Centre (it's been called everything from an art installation to 'fossil dinosaur eyes and teeth'), the slab actually contains fossilised remains of fast-swimming marine molluscs called cephalopods.

These once-abundant animals resembled modern-day squid: fierce predators with a cluster of grasping tentacles and a mechanism that shot out a jet of water to propel them through the oceans.

The fossils on the slab are from two types of cephalopod. The long, straight shells are from Orthocones, relatives of modern-day nautilus. The spiral shells are from an extinct group of cephalopods called Ammonites.

After the animals died, these shells settled on the seafloor and became buried in silty mud. The outer shell itself is not preserved, but these fossils are like x-rays of the shell's inner structure, showing the chambers that the animals used to live in. Some of these chambers were also filled with a gas for buoyancy.

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