Researchers have unearthed fossils of numerous extinct marine creatures that lived hundreds of millions of years ago, and these fossils could help understand ancient geography.
A team of scientists collected the specimens on the island of Ko Tarutao in Thailand. The fossils represent several species of a strange class of prehistoric marine animals known as trilobites.
Trilobites are similar in appearance to woodlice, with segmented bodies, half-moon-shaped heads and several limbs. More unusual is the realization that these animals may have breathed through gill like structures hanging from their legs. They formed an important part of marine ecosystems from the Early Cambrian to the end of the Permian.
In the study, the researchers identified 10 previously unknown species of trilobites that they discovered off the coast of Ko Tarutao, Newsweek reported. The team named one of the new species, Tsinania sirindhornae, after Royal Princess Maha Chakri Sirindhorn of Thailand for her support of science and interest in paleontology.
Fossils of 13 species previously found elsewhere in the world but never in Thailand were also unearthed in the area.
The trilobite fossils were found in layers of a soft, light and porous rock known as “tuff”. This rock is formed when ash or dust from ancient volcanic eruptions is compressed over time. Tuff contains crystals of a mineral known as zircon, which forms during eruptions. This mineral is hard, chemically stable and resistant to heat and weathering.
More importantly, zircon crystals also contain uranium atoms, allowing researchers to date when the mineral formed. “Using radio isotope techniques, we can date when the zircon was formed and thus find the age of the explosion as well as the fossil,” said Nigel Hughes, co-author of the latest study from the University of California, Riverside.
The rocks where trilobite fossils were found on the Ko Tarutao coast date from the latest stage of the Cambrian period (roughly 490 million to 485 million years ago) to the earliest stage of the next Ordovician period (roughly 485 to 478 million years ago).
The discovery of trilobites, which have been found in other parts of the world but not in Thailand, has enabled researchers to solve an ancient geological puzzle. “The geography of our planet has changed dramatically over time, a kind of 3D puzzle known as ‘plate tectonics’, where the pieces are constantly changing shape. Our job is to uncover the detailed history of this changing puzzle. Because it tells us how the Earth kept itself cool as a planet for millions of years, and also gives us clues about where critical mineral resources are located.”
When the Thai trilobites lived, the “puzzle piece” they were found on was located on the outer edges of Gondwana, or Gondwanaland. (An ancient supercontinent that includes Africa, South America, India, Australia, Antarctica and parts of Madagascar and China.)
The discovery of trilobites on Ko Tarutao has enabled researchers to link the slice of continental crust (known as “Sibumasu”) on which the island lies with ancient geography of Gondwana, such as parts of Australia and China. This is because the same species of trilobites have been found in these regions.
“We can connect Thailand to parts of Australia, a really exciting discovery,” said Shelly Wernette, co-author of the study and now at Texas State University.
East and Southeast Asia are geologically young regions of the continent compared to other parts of the world, such as North America. This region is also one of the least well understood geologically on Earth. This is partly because vegetation is abundant, in many places it is difficult to see the exposed rocks. It is also made up of many small ancient “micro continents” that made their own individual tectonic journeys before colliding to form East Asia.
“Our job is to identify the pieces of the puzzle that make up East Asia, where they were before and when they came together. By looking at rocks that formed in specific time periods, we learn what the pieces looked like then and how they changed later. We can assess these in a variety of ways, but this study uses the geographical distribution of ancient trilobites to do so. We study the fossils to see where similar forms formed and where their closest relatives lived.”
The team’s results revealed that the ancient continental jigsaw piece known as Sibumasu, which carried the Thai trilobites, was originally along the edge of northern Gondwana, encircling parts of western Australia and China.
“The next task is to see how this changed over time as Gondwana broke apart and what is now eastern Asia began to come together,” Hughes said.
Cover photo shows an example of tribolites, the main subject of the research that allows us to learn about ancient geography. Photo: Nobu Tamura