A single lump of rock has been found to preserve hundreds of insect fossils in exquisite detail – just one of many at a newly discovered site offering unprecedented insight into Australian ecology 11-16 million years ago.
Paleontologists estimate they have only explored around 10 percent of the richness of the new site called McGraths Flat. More remarkably, the type of rock found there has not previously been associated with good fossil preservation, and the hunt for similar examples could lead to even bigger finds.
Instead of simply capturing bones, teeth, and perhaps scales, the iron-rich goethite at McGraths Flat preserved soft and fragile parts of plants, invertebrates, and even the stomach contents of fish. Hopefully, we have much more to find at what could become one of the world’s most important fossil sites, and the distinctive geology could lead us to similar discoveries elsewhere.
For three years, scientists from a dozen institutions have secretly been digging near Gulgong in Australia’s Central Tablelands, and are now ready to reveal the site to the world. They consider it one of Australia’s very few Lagerstättes, fossil sites of global significance. In the journal Science Advances, the team describes the fossils they have found, plus the goethite rock that has created this breathtaking preservation.
“Fossils have been found in goethite before,” Dr Matthew McCurry of the Australian Museum told IFLScience, “But they were not high quality.” Consequently, paleontologists had not regarded goethite sites as promising places to look.
Then, local farmer Nigel McGrath alerted the Australian Museum that he had found fossilized invertebrates on his land. Australian fossil sites, particularly from the mid-Miocene, are rare enough that the find would have been of interest even if the preservation was only of ordinary quality. Instead, as the images show, it is breathtaking.
“We think that the process that turned these organisms into fossils is key to why they are so well preserved,” McCurry said in a statement; “Our analyses suggest that the fossils formed when iron-rich groundwaters drained into a billabong [oxbow lake], and that a precipitation of iron minerals encased organisms that were living in or fell into the water,”
For three years, a team of 15 scientists has been exploring the site. Despite being quite small, it is so rich that McCurry estimates 90 percent of the finds are still to come. Meanwhile, McCurry told IFLScience, they have begun the process of looking at other goethite deposits. “The next step is to do more research on what geochemistry and sedimentation conditions are required to produce such amazing fossils,” McCurry said. “This will tell us where to look so we can get out in the field.”
The species found at McGraths Flat are mostly rainforest natives. However, pollen found there suggests drier habitats were nearby. The fossils were laid down at a time when the continent was drying out and once widespread rainforests retreating to the coast. Consequently, we probably have a window into the last years of an abundant ecosystem before it was replaced by those better able to survive drought and fire.
McCurry told IFLScience many fossils are likely species never seen before, but the process of confirming that is a long one.
The preservation is so good that scientists are able to study internal organs – including partially digested meals, revealing predator-prey relationships. Likewise, leaf damage on plants indicates insects’ impacts. Dozens of pollen grains can be seen on the head of a sawfly, allowing identification of the plants it pollinated.
The site has yet to be dated precisely, with the four-million-year range of possibilities determined based on pollen types identified.