Palaeontologists in southern Argentina have uncovered an enormous network of fossils dating back to the Jurassic period, enabling them to reconstruct an entire ecosystem that has remained “frozen” in time for around 140 to 160 million years. The discovery occurred in the locality of La Bajada, in a region of southeast Patagonia called the Deseado Massif, where recent soil erosion across an area spanning some 60,000 square kilometers (23,000 square miles) has exposed the fossils.
All specimens have been exceptionally well preserved via silicification, which refers to the process of becoming saturated in a chemical compound called silica, normally derived from volcanic material. Since the period and location from which the fossils originate is associated with intense volcanic activity, the researchers suggest that “silicification probably occurred while organisms were alive or soon after their death.”
Since then, they have remained encased in chert, a sedimentary rock material composed of silicon dioxide that preserves soft-bodied organisms. Like amber, this has enabled scientists to obtain precious glimpses into the evolution of terrestrial environments. However, reporting their findings in the journal Ameghiniana, the study authors explain that the sheer diversity of fossils at La Bajada ensures that this discovery yields significantly more detailed information about Jurassic ecosystems than any other chert deposit ever discovered.
Collecting more than 1,000 samples from La Bajada in 2014, researchers note that the incredible abundance of fossilized plants and microorganisms allows them to reconstruct key features of the Jurassic landscape, while also identifying relationships within the local food chain.
For instance, the distribution of algae normally associated with either deep or shallow water paints a picture of the aquatic subenvironments present during the Jurassic period. Additionally, the position of certain fungi and other microorganisms in relation to host plants provides information regarding how these organisms fed on organic matter, with clear evidence of parasitic engagements.
The enormous abundance of well-preserved plant material provides a detailed insight into which species existed at the time, and how they evolved over a period of around 20 million years. This, in turn, enables researchers to identify the evolutionary roots of many modern plants and ecosystems. For example, among the species found in La Bajada are several types of fern belonging to the Osmundaceae family. Previously, scientists have struggled to determine whether fossilized fragments of these ferns found elsewhere represented different developmental stages of the same taxon, or were in fact distinct from one another in evolutionary terms.
By studying the specimens uncovered at La Bajada, the researchers hope to fill at least some of these gaps in our knowledge of how these species evolved.