Scientists have uncovered 10 species of ancient sea creatures called trilobites that were hidden for 490 million years in an underexplored area of Thailand. These fossils may provide missing pieces to the puzzle of what the world looked like long ago.

Trilobites are extinct marine animals that had crescent-shaped heads and breathed through their legs. A new 100-page research paper describes the new species in detail, including one named after Princess Maha Chakri Sirindhorn of Thailand.

The trilobite fossils were trapped between layers of petrified ash in sandstone. This rock formed on the seafloor from ancient volcanic eruptions. The eruptions deposited a green rock layer called tuff. Unlike other rock types, tuff contains zircon minerals that formed during eruptions.

Zircon is chemically stable and resistant to heat, weathering, and erosion. It’s as hard as steel and survives when other minerals break down. Within zircon crystals, individual uranium atoms slowly decay into lead atoms over time.

We can use radioisotope dating techniques to determine when the zircon formed, which tells us the age of both the eruption and the fossil, explains Nigel Hughes, co-author of the research paper and professor of geology at University of California Riverside.

It’s rare to find tuff from this specific period, called the Late Cambrian between 497-485 million years ago. There aren’t many places in the world that have this. It’s one of the Earth’s most poorly dated time intervals, said Hughes.

The tuff will allow us not only to date the fossils we found in Thailand, but also gain a better understanding of places like China, Australia, and even North America, where similar fossils have been found in undatable rocks, said Shelly Wernette, a former student of Hughes now at Texas State University, and lead author of the research.

The fossils were discovered on Ko Tarutao island off Thailand’s coast. As part of a UNESCO geopark, the area has drawn international science teams to study it. For Wernette, finding 12 types of trilobites also seen elsewhere was especially exciting – Now we can connect Thailand to parts of Australia, a really cool discovery.

During the trilobites’ time, this region was on the outer edge of Gondwanaland, an ancient supercontinent including Africa, India, Australia, South America, and Antarctica.

As continents drift over time, part of our work has been figuring out where this area of Thailand was relative to the rest of Gondwana, explains Hughes. It’s a 3D puzzle that moves and reshapes. This discovery will help us solve it.

For example, the species named after Princess Sirindhorn. The royal name honors her dedication to Thai science. I also thought this species had a regal quality, with a wide head crest and clean lines, says Wernette.

If researchers can date the tuff containing the related species Tsinania sirindhornae, they may show these northern and southern Chinese Tsinania lived at the same time.

Ultimately, the researchers believe the ancient world glimpses hidden in the fossils they’ve uncovered hold valuable information today. What we have here is a record of evolutionary changes and extinctions written by Earth for us, and we’re lucky to have it. The more we learn from it, the better prepared we’ll be for the challenges our planet faces now, said Hughes.


University of California, Riverside | Wernette, S.J., Hughes, N.C., Myrow, P.M. and Sardsud, A. (2023), Trilobites of Thailand’s Cambrian–Ordovician Tarutao Group and their geological setting. Pap Palaeontol, 9: e1516.

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