A trilobite rises from the ashes to reveal an ancient map
Ten newly discovered species of trilobite, hidden for 490 million years in a little-studied part of Thailand, may be the missing pieces in a complex puzzle of ancient world geography.
Trilobites are extinct marine creatures that have half-moon-shaped heads and breathe through their legs. A 100-page study in the British Journal provides fascinating details about the new species, including one named in honor of Thai Princess Royal Maha Chakri Sirindhorn.
The trilobite fossils were trapped between layers of fossilized ash in the sandstone, the product of ancient volcanic eruptions that settled on the sea floor and formed a green layer called tuff. Unlike some other types of rocks or sediments, stones contain crystals of zircon – a mineral that forms during a volcanic eruption and, as the name of the rock layer it contains suggests, is hard.
Zircon is chemically stable as well as heat and weather resistant. It is as hard as steel and persists when minerals found in other types of rocks wear away. Within these flexible zircon crystals, individual uranium atoms gradually decay into lead atoms.
“We can use radioisotope techniques to date the formation of the zircon and thus determine the age of the eruption, as well as the fossil,” said Nigel Hughes, co-author of the study and professor of geology at the University of California, Riverside.
It is rare to find mutations from this particular time period, the Late Cambrian, between 497 and 485 million years ago. “There aren’t a lot of places around the world that have this. It’s one of the worst time periods in Earth’s history,” Hughes said.
“The stones will allow us not only to determine the age of the fossils we found in Thailand, but to better understand parts of the world such as China, Australia and even North America where similar fossils have been found in rocks that cannot be dated.” said Shelley Wernett, a former geologist at Hughes Lab who now works at Texas State University and first author of the study.
The fossils were discovered on the coast of an island called Ko Tarutao. It is located about 40 minutes southwest of the mainland via high-speed boat and is part of a UNESCO geopark site which has encouraged international teams of scientists to work in this area.
For Vernet, the most interesting discovery was 12 species of trilobites that had been seen in other parts of the world, but had never been seen in Thailand before. “We can now connect Thailand to parts of Australia, which is a really exciting discovery.”
During the life of the trilobite, this region was on the outer edges of Gondwanaland, an ancient supercontinent that included Africa, India, Australia, South America and Antarctica.
“Because continents change over time, part of our mission was to determine the location of this region of Thailand compared to the rest of Gondwanaland,” Hughes said. “It’s a 3D, shape-shifting, moving jigsaw puzzle that we’re trying to put together. This discovery will help us do that.”
For example, take the species named after the royal princess Sirindhorn. The species was named in honor of the princess for her unwavering dedication to the development of science in Thailand. “I also thought this species had a regal quality. It has a broad headdress and clean sweeping lines,” Wernett said.
If researchers can get a history of rafts containing the species of the same name, Tsinania sirindhornae, and determine when they lived, they will be able to say that the closely related species of Tsinania found in northern and southern China are roughly the same age.
Ultimately, researchers feel that the images of the ancient world hidden in the fossils they find contain information that is invaluable today.
“What we have here is a record of evolutionary change accompanied by extinction. The Earth wrote this record for us, and we are lucky to have it,” Hughes said. “The more we learn from it, the more prepared we will be to meet the challenges we on this planet design for ourselves today.”
(Cover image: Aunt_Spray/iStock/Getty)