These fossils allow us to redraw the map of the Gondwana – Futura supercontinent

490 million years ago, Thailand was part of Gondwana. But where exactly was this little piece positioned? The recent discovery of trilobite fossils helps answer this question and establishes the late Cambrian connections with other parts of this supercontinent.

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490 million years ago, Earth’s landscape was far removed from what we know today. We are then at the end of the Cambrian, a very critical period in the history of life on Earth. The supercontinent Pannotia has completed its fragmentation, creating space for several lithospheric megaplates named Laurentia, Baltica, Siberia and the largest: Gondwana.

The latter include the lands that hundreds of millions of years later will form South America, Africa, Antarctica, Australia, Arabia, India and the recently mapped continent of Zealandia. A variety of small animals thrive in the vast oceans that separate these four major continental masses. Among them are trilobites. These armored arthropods diversified very quickly in the Cambrian and colonized all oceans. They will eventually die out during the mass extinction that marked the end of the Permian and the entry into the Mesozoic Era, 251 million years ago. Today, trilobite fossils are certainly the most symbolic finds of the Paleozoic. Fossils that are of great interest in reconstructing the evolution of the continents in this distant period.

Fossils connect the pieces of the great tectonic puzzle

In fact, the continents are constantly moving, driven by the continuous formation of oceanic crust at the level of the ridges. Thus, these movements can be reconstructed thanks to the magnetic anomalies that are gradually being recorded in the rocks of the oceanic crust. A method that works wonderfully, but only for the last 200 million years! It is impossible to go beyond that. And for good reason: oceanic crust is continually recycled at subduction zones. There is currently no oceanic magnetic anomaly on Earth that is older than 200 million years. Therefore, to reconstruct the history of the continents beyond this date, scientists must find other clues. Fossils and especially trilobites with their impressive diversity can contain a lot of information in this context.

Fossils that help reconstruct the mystery of Gondwana

In this way, the discovery of trilobite fossils made it possible to correctly place Thailand’s location in the great tectonic puzzle that is Gondwana. The fossils were found on the Thai island of Ko Tarutao in a layer of ash that was originally deposited on the seafloor during a volcanic eruption. However, volcanic ash contains zircons, small, very resistant minerals whose radioisotope analysis made it possible to date the eruption and at the same time the fossils.

The trilobites would therefore be around 490 million years old (end of the Cambrian). The identified species are new to Thailand, but have already been found in other regions of the world, particularly Australia and northern and southern China. This new paleontological discovery, published in the journal Palaeontology, makes it possible to connect several pieces of the Gondwana tectonic puzzle. A connection with the continent of Laurentia (today’s North America), where certain undated specimens were found, also seems possible.

490 million years ago, this region of Thailand was part of the outer edge of the supercontinent Gondwana. The discovered trilobite fossils therefore help to draw a more accurate map of Earth’s geography at the end of the Cambrian.