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After dinosaurs, trilobites are perhaps the most recognizable fossil animals (SN: 9/27/23). They proliferated in the ocean for about 270 million years before going extinct at the end of the Paleozoic era, some 252 million years ago.
Trilobite fossils are extremely common because their hard exoskeletons make it relatively easy for the animals to become fossils. But just as it’s rare to discover any trace of soft-tissue preservation in dinosaurs, so it is with trilobites.
To uncover how these trilobites and their tissues became so well preserved, Paterson and his team enlisted Robert Gaines, a geologist at Pomona College in Claremont, Calif., and an expert in how the soft parts of animals become fossils.
It happened like this: First a volcano exploded, and superheated ash flowed from the eruption into nearby coastal waters. The ash dissolved and then remineralized out of the water, covering the exposed trilobites and entombing them in a matter of hours to days.
The key step in this process, Gaines says, is that the ash hit water before hardening around the trilobites; without the cooling effects of ocean water, the hot ash would have burned the trilobites away.
Gaines studies similar fossil preservation in other, older fossils, such as an arthropod called Aegirocassis, an alien-like animal with what appears to be a strange baleen-style feeding apparatus (SN: 3/11/15). “I recognized the similarities immediately,” Gaines says. “They pointed to the same process operating more than 20 million years earlier.”
Besides being ready for a museum showcase, the fossils open new…
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