Fossils Help Redraw the Map of the Supercontinent Gondwana

gondwana

Approximately 490 million years ago, Thailand was a part of the Gondwana supercontinent. The recent discovery of trilobite fossils provides insight into the specific positioning of this landmass during the late Cambrian period and its connections with other parts of the supercontinent.

At that time, the Earth’s landscape vastly differed from what we observe today. The late Cambrian marked a critical period in the history of terrestrial life, following the fragmentation of the Pannotia supercontinent. This gave rise to several megalithospheric plates, including Laurentia, Baltica, Siberia, and the largest one, Gondwana.

Within Gondwana were the landmasses that, hundreds of millions of years later, would form South America, Africa, Antarctica, Australia, Arabia, India, and the recently mapped continent of Zealandia. In the expansive oceans separating these continents, various small animals thrived, among them the trilobites. These carapace-armored arthropods underwent rapid diversification during the Cambrian and colonized oceans worldwide. Their extinction occurred during the Permian mass extinction, marking the transition to the Mesozoic era, approximately 251 million years ago. Today, trilobite fossils are emblematic of the Paleozoic era, offering valuable insights into the evolution of continents during that distant period.

Fossils Unraveling the Tectonic Puzzle

Artist's view of a trilobite, an emblematic species of the Paleozoic era.© Nobu Tamura
Artist’s view of a trilobite, an emblematic species of the Paleozoic era.© Nobu Tamura.

The ongoing formation of oceanic crust at mid-ocean ridges is what propels continents’ constant motion. The reconstruction of these movements relies on magnetic anomalies recorded in oceanic crust rocks. However, this method is effective only for the past 200 million years, as oceanic crust is continuously recycled at subduction zones. Beyond this timeframe, scientists must employ alternative approaches. Fossils, particularly trilobites, with their remarkable diversity, can provide significant information in this context.

Fossils Reconstructing the Gondwana Puzzle

Paleogeographic reconstruction of Gondwana. The island of Ko Tarutao is indicated by an arrow, in contact with what would later become Australia. Wernette et al. 2023, Palaeontology

The discovery of trilobite fossils has accurately positioned Thailand within the Gondwana tectonic puzzle. These fossils were found on the Thai island of Ko Tarutao under a layer of volcanic ash that was formed during a volcanic eruption. They were dated by radioisotopic analysis of zircon minerals in the volcanic ash, which showed that they are about 490 million years old (late Cambrian). While the identified species are new to Thailand, they have been found in other regions globally, including Australia, as well as the northern and southern parts of China.

Published in the Palaeontology journal, this paleontological discovery contributes to connecting various pieces of the Gondwana tectonic puzzle. A potential link with the Laurentia continent (present-day North America), where some undated specimens have been found, also emerges.

Therefore, 490 million years ago, the Thai region was part of the outer margin of the Gondwana supercontinent. The discovered trilobite fossils aid in creating a more precise map of the Earth’s geography at the end of the Cambrian period.