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Trilobites are strange creatures: they resemble giant insects swimming in helmets and have lived on Earth for 270 million years. These armored invertebrates, whose species once numbered in the thousands, thrived in the oceans while foraging and digging, even managing to survive two mass extinctions.
But about 252 million years ago, trilobites disappeared from the fossil record. What finally wiped out this class of resilient bottom dwellers?
The disappearance of the trilobite coincided with the end of the Permian extinction (also known as the Permian-Triassic extinction), the third and most devastating mass extinction event. Volcanic eruptions in Siberia have spewed huge amounts of lava for about 2 million years, according to Melanie Hopkins, associate curator of paleontology at the American Museum of Natural History in New York City. These fiery eruptions sent trillions of tons of carbon dioxide into the atmosphere, igniting themselves acidification of the oceans, which in turn made the survival of marine animals very difficult, according to a 2010 article published in the journal Proceedings of the National Academy of Sciences. Up to 95% of marine species succumbed to extinction in the late Permian, also known as the Great Dying, including trilobites.
Related: How long do most species last before becoming extinct?
The trilobites, however, had already started a downward spiral towards extinction by that point. “When it comes to this mass extinction, there aren’t many trilobites around,” Hopkins told LiveScience. This is because environmental and evolutionary changes had been reduced to this class of creatures.
Hopkins studies changes in the shape and size of the trilobites’ body over time and how these factors affected their survival. When trilobites first emerged in early Cambrian period (541 million to 485 million years ago), they were extremely diverse, potentially because there weren’t many competitors, Hopkins said. Adaptations of trilobites during the early Cambrian were primarily related to growth and development, as were variations in the number of segments or limbs they had.
But during the Ordovician period, starting around 485 million years ago, competition and predation came into play more than before. At this time “many [trilobite] Adaptation is clearly related to ecology, “Hopkins said. Some trilobites have developed different eye placement, harder exoskeletons, or the ability to roll into a ball. These adaptations, paleontologists suspect, have made trilobites more effective. on the increasingly competitive ocean floor.And in the long run, these pressures could have limited the trilobites’ recovery from impending mass extinctions.
Then came the world’s first mass extinction: the Ordovician-Silurian extinction about 444 million years ago, caused by global cooling and a drop in sea level, according to the University of California’s Department of Earth Sciences. southern. The number of trilobite species, once in thousands, has dropped by the hundreds, according to American Museum of Natural History. Although food webs and ecosystems have remained intact, the trilobites “never fully diversify or reach previously achieved numbers,” Hopkins said. Increased competition in their ocean habitats may be what kept them from a full rebound.
The second mass extinction, the Late Devonian, affected trilobites starting around 375 million years ago. The extinction of the late Devonian was slower and the cause less specific than the earlier and later. It’s harder to study because it happened for a long time, Hopkins said, but it likely led to a slowdown in evolution and diversification. Although the direct cause is less clear, the effect of the second extinction on the trilobites was profound. Entire orders – in biology, animals are classified into orders, families, groups and, finally, species – went extinct. After the second extinction, only one family remained in the Trilobite class: the Proteus’.
“That’s all that was left,” Hopkins said.
It is not clear what he did Proteus’ so durable. They were relatively simple creatures compared to some more massive and monstrous trilobites that have existed. With the third extinction, the end of the Permian, competition, predators and environmental changes had turned the odds against ancient Proetida. They couldn’t resist the global warming events set in motion by volcanic eruptions.
The specifics of what made the trilobites so hardy and so vulnerable is still much under study. One way to learn more about why they went extinct, Hopkins said, “is to understand why they never diversified to the same extent. But that question remains unanswered.”
Originally published on LiveScience.
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