465-million-year-old horseshoe crab fossils discovered in Saudi Arabia's AlUla

Dubai: The Royal Commission for AlUla has announced the documentation and publication of a rare fossil discovery of horseshoe crabs dating back approximately 465 million years, following a peer-reviewed scientific study published in the geology journal Gondwana Research.

The discovery, published for the first time at a global level, strengthens AlUla’s standing as an international centre for geological and scientific research related to Earth’s history and biodiversity. The fossils were uncovered in the Gharameel Nature Reserve in AlUla.

Dating to the Middle Ordovician period, roughly between 485 and 444 million years ago, the fossils are among the oldest known horseshoe crab specimens worldwide. They are distinguished by their unusually large size compared with other species from the same era. All specimens were found preserved upside down, a mode of fossilisation not previously recorded, alongside trace fossils indicating attempts by the organisms to right themselves.

Geological layer analysis suggests the area was subject to repeated strong seasonal storms, indicating that these ancient creatures gathered in shallow coastal environments affected by such events, which contributed to their preservation within sedimentary deposits.

The findings provide a clearer picture of AlUla’s ancient environment as a coastal region and add a new scientific dimension to understanding its geological and environmental history. The commission said the analysis demonstrates its ability to generate accurate data that supports scientific research and innovation.

The discovery also represents a previously undocumented species that has yet to be formally classified. Research has been conducted in two phases in collaboration with a team led by Dr Russell Bicknell of Flinders University. The second phase, scheduled for the first half of 2026, will involve the collection of additional samples and further study prior to official classification. The fossil samples have been preserved within the commission’s museum collections to support future research and public engagement.

The commission said the discovery reflects its commitment to advancing scientific research and reinforcing AlUla’s position as a global destination for geological discovery, international collaboration and education linked to natural heritage, in line with the objectives of Saudi Vision 2030.