The odds of any individual organism making it into the fossil record are, frankly, terrible. Leaving aside the fact that some animal may eat you and scatter your remains, there’s the menace of rot to contend with, as the same oxygen that keeps animals alive also fuels the bacteria that decompose organic matter. Your best bet, if you want to be immortalized in the rock record and puzzled over by future beings, is to be buried—and quickly—in a low-oxygen environment.

The rare crown jewels of the fossil record are rocks that were deposited in conditions so ideal that details of soft tissue structures can be seen. These exquisite bonanzas are obviously terribly interesting and useful to paleontologists, whether they hold feathered dinosaurs or some of the earliest animals in evolutionary history.

In 1909, Charles Doolittle Walcott stumbled on an incredible outcrop of shale in the Canadian Rockies that pulled back the curtain on some of the organisms produced by the Cambrian explosion of life. This group of organisms, dubbed the Burgess Shale biota, included the iconic trilobite as well as the downright weird (and aptly named) Anomalocaris and Hallucigenia. In 1984, similar but slightly older rocks in China began yielding the Chengjiang biota, increasing the wealth of Cambrian organisms known to science.

Now, following on the heels of a discovery of some fossils higher up in the same rock formation that hosted the Burgess Shale biota, researchers led by the Royal Ontario Museum’s Jean-Bernard Caron think they’ve hit a new motherlode nearby. In a two meter thick section of shale, the researchers have recovered over 3,000 specimens of 55 different organisms—and that’s with only 15 days of collection so far.

Those organisms, which lived on or near the shallow seafloor, include lots of arthropods, but also worms, mollusks, and a creature with a primitive spinal cord. Two-thirds of the organisms are familiar from the old Burgess Shale site, but a dozen are new to science. In a surprise, some of the other known ones had only been seen in Chengjiang. That means they were around longer and over a wider area than previously realized.

Also of interest are the things they didn’t find many of. Non-mobile organisms like sponges and brachiopods are quite common at the old Burgess Shale and Chinese sites, but they are hard to find in this one. That shows that, even though the setting these creatures lived in was very similar to the old Burgess Shale site just 40 kilometers away, the habitat was different enough that the biological community was noticeably different, too.

It’s not just the roster of fossils that has the researchers excited—some fantastic details of the creatures’ innards have been preserved. One specimen (photo e in the top image) appears to show the structure of the eyes, heart, and liver. Others display neural tissue (photos p and q), digestive organs (photo k), and one creature’s last lunch (photo s).

This new find clearly has the potential to generate many discoveries as researchers examine the specimens they have and dig out more. It also demonstrates that the lower portion of this rock formation, where the old Burgess Shale biota fossils came from, isn’t the only section holding buried treasure. There’s a good chance there are even more amazing Cambrian fossil caches waiting to be found elsewhere in those Canadian rocks.

Nature Communications, 2014. DOI: 10.1038/ncomms4210 (About DOIs).

Listing image by Jean-Bernard Caron, Nature Communications