In a 100-page monograph published in the journal Papers in Palaeontology, paleontologists have described ten new species of trilobites from the tuff-bearing Cambrian-Ordovician layers of Ko Tarutao island, Satun province, southernmost peninsular Thailand.
Trilobites are extinct arthropods that dominated the faunas of the oceans of the Paleozoic era. During their time on Earth, which lasted much longer than the dinosaurs, between 521 and 252 million years ago, they survived two major episodes of mass extinctions and dominated ocean floor ecosystems. There are more than 20,000 known trilobite species.
“Unlike some other kinds of rocks or sediment, tuffs contain crystals of zircon — a mineral that formed during an eruption and are, as the name of the rock layer containing them suggests, tough,” said University of California, Riverside’s Professor Nigel Hughes and colleagues.
“Zircon is chemically stable as well as heat and weather resistant. It is hard as steel and persists when minerals in other kinds of rocks erode.”
“Inside these resilient zircon crystals, individual atoms of uranium gradually decay and transform into atoms of lead.”
“We can use radio isotope techniques to date when the zircon formed and thus find the age of the eruption, as well as the fossil,” Professor Hughes said.
“It is rare to find tuffs from this particular period of time, the Late Cambrian period, between 497 and 485 million years ago.”
“Not many places around the world have this. It is one of the worst dated intervals of time in Earth’s history.”
“The tuffs will allow us to not only determine the age of the fossils we found in Thailand, but to better understand parts of the world like China, Australia, and even North America where similar fossils have been found in rocks that cannot be dated,” said Dr. Shelly Wernette, a geologist at Texas State University.
The newly-described trilobite species are Tsinania sirindhornae, Pseudokoldinioidia maneekuti, Pagodia uhleini, Asaphellus charoenmiti, Tarutaoia techawani, Jiia talowaois, Caznaia imsamuti, Anderssonella undulata, Lophosaukia nuchanongi and Corbinia perforata.
The fossils were uncovered on the coast of Ko Tarutao island in the Thai province of Satun.
“The most interesting discovery was 12 types of trilobites that have been seen in other parts of the world, but never in Thailand before,” Dr. Wernette said.
“We can now connect Thailand to parts of Australia, a really exciting discovery.”
“During the trilobites’ lifetime, this region was on the outer margins of Gondwanaland, an ancient supercontinent that included Africa, India, Australia, South America, and Antarctica.”
“Because continents shift over time, part of our job has been to work out where this region of Thailand was in relation to the rest of Gondwanaland,” Professor Hughes said.
“It’s a moving, shape shifting, 3D jigsaw puzzle we’re trying to put together. This discovery will help us do that.”
Ultimately, the paleontologists feel that the pictures of the ancient world hidden in the fossils they found contain invaluable information for the present day.
“What we have here is a chronicle of evolutionary change accompanied by extinctions. The Earth has written this record for us, and we’re fortunate to have it,” Professor Hughes said.
“The more we learn from it the better prepared we are for the challenges we’re engineering on the planet for ourselves today.”
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Shelly J. Wernette et al. 2023. Trilobites of Thailand’s Cambrian-Ordovician Tarutao Group and their geological setting. Papers in Palaeontology 9 (5): e1516; doi: 10.1002/spp2.1516
