The Humble Trilobites

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If you think it is impressive that primates have managed to survive on Earth for 50 million years, then you will find it phenomenal that trilobites managed to survive for a staggering period of 270 million years. First appearing on Earth about 521 million years ago during the early Cambrian period (when life on Earth began to complexify in incredible ways), they finally became fully extinct around 252 million years ago, during the late Permian period, and were probably the most abundant animal on Earth at that time. This is one testament to their immense success as an organism; another being the fact that their fossils are found widely dispersed on Earth – on every continent in fact – and palaeobiologists have named over 15,000 species of trilobites. So what made them so successful as an organism?

For one thing, trilobites were the first true arthropods, meaning they had a tough, segmented exoskeleton that covered its body, like insects and arachnids do today. Before the trilobites, life on Earth mostly existed as squishy organisms, such as jellyfish and sponges. The segmented nature of their exoskeleton allowed them to curl up (like armadillos!) to protect themselves from predators, and when these predators developed jaws that could crunch through the trilobites’ exoskeleton, they developed spikes and spines in retaliation.

Trilobites also had a multitude of segmented legs, which enabled them to move around the ocean floor, where they spent their time and thrived for hundreds of millions of years. They also had a developed digestive system, allowing them to feast on a diet of worms and other invertebrates.

But the most impressive of their adaptations would have to be their eyes. For early organisms, they had eyes that were incredibly complex. The lenses in human eyes are flexible and able to change shape so we can focus alternately on things close to and far away from our eyes. Because the trilobites lenses (they can have up to 1000 of them) are made of calcite, a crystal (a crystal in your eye!), their lenses’ shape is fixed, which means they can’t to focus on things at different distances from themselves. There’s also another problem. The fixed lens shape results in weird distortions of light and images that come through. This problem can only be resolves if the lens is a very particular shape, a shape that two astronomers (Christiaan Huygens and Rene Descartes) in the 1600’s came up with. The diagrams of these inventions, as well as the lens shapes of two trilobite species are shown below. As you can see, what’s incredible is that the two shapes are unnervingly similar. The trilobite had no trouble seeing, because the shapes allowed them to focus on things close by as well as far away, and for things to be minimally distorted through the lenses. To put it in Hank Green’s words, “It took humans 300 million years to catch up with trilobite evolution!”

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The trilobite, a humble organism from hundreds of millions of years ago, was so complexly developed that it survived for 270 millions years, and took Mother Earth 4 different extinction events to finally cause all the trilobites to go extinct. For more information on the trilobite, check out the PBS Digital show Eons on Youtube, where they explore the history of all life on Earth.

Written by Khanh Nguyen, Year 11

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