How Hidden Fossils in Museums Are Rewriting Evolutionary History

For centuries, museums have acted as vaults of human knowledge, preserving the artifacts of our past—from ancient manuscripts to long-extinct creatures. Yet within their storerooms, locked away in cabinets and drawers, lie countless fossils that have never been published, never included in scientific databases, and never made their way into our understanding of evolution.

A new study, published on February 26, 2025, in Proceedings of the Royal Society B, reveals the profound impact that these “dark data” fossils—specimens stored in museums but absent from the scientific literature—can have on evolutionary research. Researchers Christopher D. Dean and Jeffrey R. Thompson examined fossil records of ancient sea urchins, known as echinoids, from 33 museums worldwide. When they incorporated these overlooked specimens into existing datasets, they discovered that global patterns of biodiversity, species distributions, and even evolutionary conclusions changed significantly.

What Are “Dark Data” Fossils, and Why Do They Matter?

Palaeontologists today rely heavily on digital databases like the Paleobiology Database (PBDB), which compiles fossil records from published research. This means that when a scientist studies the evolution of a species over millions of years, they often draw conclusions from what is available in these databases—assuming that the published record reflects reality.

But here’s the problem: museums hold vast collections of fossils that were collected, labeled, and stored but never formally studied or published. These specimens remain “dark data”—invisible to the scientific community simply because they have not been written about. Some were collected decades ago by geologists or fossil hunters with no intention of publishing their findings. Others belong to groups that, for whatever reason, have received less attention in scientific literature.

The consequences of this missing data are significant. Imagine trying to understand the migration patterns of birds today but only having access to records from a few select regions. If you lacked data from entire continents, your conclusions would be skewed. The same applies to fossils.

What the Study Found: A Larger and More Complex Past

Dean and Thompson focused on echinoids from the Palaeozoic era (541–252 million years ago). By comparing three datasets—(1) fossils from published studies, (2) data from the PBDB, and (3) unpublished museum fossils—they uncovered striking differences:

• Species’ geographic ranges expanded by 35% when museum fossils were included. In other words, our current databases vastly underestimate where these animals once lived.
• Biogeographic models changed. Previously, it appeared that some species were restricted to certain regions, but “dark data” revealed they had much wider distributions.
• Overall diversity estimates remained stable. This means that while the number of known species didn’t dramatically increase, the understanding of where they lived and how they spread across ancient ecosystems did.

This last point is particularly interesting. While museum fossils didn’t suddenly reveal a flood of unknown species, they did alter how scientists interpret the evolutionary history of those species. This suggests that museum collections contain essential missing pieces—not in the form of new species, but in the details of their ecology, migration, and extinction patterns.

How Scientific Bias Shapes the Fossil Record

The study also highlights a long-standing issue in palaeontology: historical biases in fossil collection and research. Most museum collections, particularly those studied in this paper, are concentrated in North America and Europe. This reflects a colonial legacy in the sciences—where fossils from the Global South were often extracted and shipped to European and North American institutions.

This geographical imbalance in data has consequences. It means that our current understanding of prehistoric life is shaped primarily by fossils collected from certain regions, while vast areas of the world remain underrepresented. As the authors note, integrating museum fossils from underrepresented regions could provide a much more accurate and global view of evolution.

What This Means for the Future of Palaeontology

The implications of this research extend far beyond sea urchins. If unpublished museum fossils can dramatically alter biogeographic models for one group, they are likely to do the same for many others. The study calls for a renewed effort in museum digitization, ensuring that the wealth of information hidden in collections is integrated into modern datasets.

Why does this matter? Because understanding the past is essential for predicting the future. Scientists use the fossil record to model biodiversity loss, climate change responses, and extinction risks. If these models are based on incomplete data, their predictions may be flawed.

This study reminds us that palaeontology is not just about finding new fossils—it’s about properly using the ones we already have. The past, it turns out, is still waiting to be discovered, hidden in museum cabinets around the world.