Trilobites: Enduring Success and Mysterious Extinction of Ancient Arthropods

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Trilobites: Enduring Success and Mysterious Extinction of Ancient Arthropods

Clip title: The Trouble With Trilobites Author / channel: PBS Eons URL: https://www.youtube.com/watch?v=Aji2VnQFUCs

Summary

Trilobites, recognizable fossils found globally, were incredibly successful marine arthropods that thrived for over 270 million years. This video from Eons explores not just their eventual extinction, but rather the remarkable ways they survived multiple catastrophic events throughout Earth’s ancient history, making their ultimate disappearance a compelling mystery. They were once the planet’s most abundant animals, found scouring ocean floors from Siberia to Australia.

Emerging about 521 million years ago during the Cambrian Period, trilobites are thought to have evolved from simpler, thick-skinned segmented worms like Spriggina. They rapidly developed complex features, including jointed legs, sophisticated compound eyes, and a robust exoskeleton made of calcite and chitin. As true arthropods, they were pioneering members of a group that would eventually include modern spiders, crabs, and insects. Their physical complexity and diverse diet of worms and other invertebrates allowed them to dominate the Cambrian seas, quickly diversifying into at least 60 taxonomic families. When predation first appeared, trilobites adapted by developing the ability to ‘enroll’ or curl into protective balls, much like modern pillbugs, offering a vital defense against new threats.

Trilobites faced two more major extinction events before their final demise. The Ordovician-Silurian Extinction, approximately 445 million years ago, was triggered by a dramatic global cooling and glaciation, which altered ocean currents and significantly lowered sea levels. This event wiped out about a quarter of all taxonomic families, including roughly half of the trilobite families. However, surviving trilobite lineages, such as Dalmanites, adapted to the cooler waters and continued to thrive. Later, during the Devonian Period around 420 million years ago, the emergence of jawed fish introduced a new, formidable class of predators. In response, trilobites again evolved, developing defensive features like elaborate spines and spiky exteriors, exemplified by species like Dicanurus, to deter these new threats.

Despite their extraordinary resilience, the trilobites met their end during the Permian Period, approximately 252 million years ago, in what is known as ‘The Great Dying’ – the most severe extinction event in Earth’s history. While the exact cause remains debated (asteroid impact, massive volcanism, shifting landmasses altering climate), the effects were devastating. Within a million years, 70% of land species and a staggering 95% of marine species vanished, including the last remaining trilobite species. The video concludes that the real marvel of trilobites isn’t their extinction, but their unparalleled longevity and adaptability, having endured for longer than non-avian dinosaurs and even mammals have existed. Their history serves as a powerful reminder of how environmental changes and evolutionary pressures can shape life, and perhaps, a cautionary tale for humanity as one of Earth’s current dominant species.

Video Description & Links

Description

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Trilobites are famous not just because they were so beautifully functional, or because they happened to preserve so well. They are known the world over because they were everywhere!

This episode was written by Blake de Pastino.

Thanks to Franz Anthony, Julio Lacerda, Lucas Lima and Studio 252mya for their illustrations. You can find more of their work here: https://252mya.com/licensing

Produced for PBS Digital Studios.

References: http://scienceline.ucsb.edu/getkey.php?key=1279 https://www.uky.edu/KGS/fossils/trilob_fact_sheet.pdf https://www.scientificamerican.com/article/3-billion-to-zero-what-happened-to-the-passenger-pigeon/ http://www.trilobites.info/geotime.htm http://www.trilobites.info/origins.htm http://io9.gizmodo.com/5145786/trilobites-the-greatest-survivors-in-earths-history https://trilobite94.wordpress.com/trilobites-important-fossil-localities/ http://www.cornellcollege.edu/geology/courses/greenstein/paleo/trilobites.pdf https://science.nasa.gov/science-news/science-at-nasa/2002/28jan_extinction http://www.els.net/WileyCDA/ElsArticle/refId-a0001653.html http://www.amnh.org/our-research/paleontology/paleontology-faq/trilobite-website/the-trilobite-files/the-last-trilobites http://www.trilobites.info/lasttrilos.htm http://evolution.berkeley.edu/evolibrary/article/_0/success_03

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Trilobites: Enduring Success and Mysterious Extinction of Ancient Arthropods

Trilobites: Enduring Success and Mysterious Extinction of Ancient Arthropods