New PACA tool makes ancient fossil mapping accessible to all researchers

A fossil discovered in one location today may have formed thousands of miles away, millions of years ago. Tectonic plates have spent Earth's entire history in motion, carrying continents and ocean floors across the planet's surface. For paleontologists trying to understand where an ancient organism actually lived, reconstructing that original geography has always required specialized software, coding knowledge, and a deep familiarity with how different models describe plate movement. A team at the University of Barcelona has just removed that barrier.

The Paleocoordinates Calculator, or PACA, is a free web tool that takes a fossil's current location and geological age, then calculates where that spot sat on the ancient Earth. Users upload a simple spreadsheet with modern longitude, latitude, and age estimates—no programming required, no software installation needed. Within seconds, the tool returns the reconstructed ancient coordinates, displayed both in tables and on interactive three-dimensional paleogeographic globes. The researchers, led by Noa Scholz-Murcia and Antonio Monleón-Getino from the university's Faculty of Biology, published their work in Scientific Reports.

What makes PACA genuinely useful is how it handles uncertainty. No single model of plate tectonics perfectly describes how every piece of Earth's crust has moved through geological time. Different models rely on different evidence, different assumptions, different reference frames. PACA lets users compare five established models simultaneously—PALEOMAP, GOLONKA, MERDITH2021, TorsvikCocks2017, and MATTHEWS2016_pmag_ref—and see where they agree and where they diverge. For each fossil location, the tool calculates the geographic distance between the most distant model predictions, measured in kilometers. A fossil might stay within tropical latitudes under every model, or it might shift between climate zones depending on which reconstruction you trust. That variability is not a flaw; it's essential information. It tells researchers where tectonic history is well understood and where it remains genuinely uncertain.

The technical foundation is solid. PACA connects to the GPlates Web Service, which applies mathematical rotations describing how tectonic plates have moved. Rather than using pre-calculated grids that average positions across roughly 100-kilometer squares, PACA reconstructs each location individually, preserving precision. The team validated the tool against 142 fossil sites distributed worldwide across a broad range of geological ages. Median spatial errors ranged from 6.25 to 16.8 meters across the five models—negligible on a planetary scale, where tectonic reconstructions typically carry uncertainties measured in tens or hundreds of kilometers. The agreement with traditional desktop software was nearly perfect, with no evidence of systematic bias.

The practical implications are substantial. Paleontologists can now place fossil discoveries in their original geographic settings without becoming software engineers. Teachers and students can explore ancient species ranges and examine whether organisms crossed climate zones or tectonic boundaries. Large datasets can be processed while keeping the reconstruction method visible and reproducible. The tool's model-comparison features also encourage a healthier scientific mindset: treating reconstructed locations as estimates rather than fixed facts, acknowledging that plate histories remain uncertain in many regions.

The researchers have made the source code, conversion scripts, and visualization files publicly available through Zenodo, supporting reproducibility and providing a reference point if the underlying web services or tectonic models change in the future. They do caution that PACA depends on the live GPlates Web Service, and future updates to rotation files could slightly alter results. Users should record the access date, selected model, and reconstruction age, and preserve downloaded data as a permanent record. By combining established tectonic models, automated calculations, and three-dimensional visualization, PACA has lowered a major technical barrier without sacrificing mathematical accuracy. The barrier that once kept paleographic analysis confined to specialists with coding skills and expensive software has simply dissolved.