Earth Science Week, Fossil Day: Ruffin’s Slab
North Carolina has good localities for Mesozoic fossils, but the most enigmatic and, to me, most interesting ones are from the Proterozoic (once called Precambrian). The Ediacaran Period is part of the latest Proterozoic, often called the Neoproterozoic. The Cambrian is still the Cambrian, and at the base of the Cambrian is what is often called the “Cambrian Explosion.” At that point in the Earth’s history, animals developed hard parts that could be easily fossilized.
Before that? The Cambrian Explosion actually had a very long fuse. Life existed, but without the hard parts that fossilize and leave us a record. So what is found in the Proterozoic are casts and molds of soft-bodied life forms, and the tracks and trails that some of them made. (We’ll leave aside all the geochemical data regarding stratigraphy and living organisms in the Proterozoic.)
There are about 30 places in the world that you find Proterozoic fossils. One of those places is the Ediacara Hills in Australia, which gives its name to the Ediacaran Period and Ediacaran Biota. Another one of those thirty places is Stanly County, North Carolina. It’s part of the exotic Carolina Terrane, a Proterozoic island arc that slammed into the edge of North America as part of the collisions that built the Appalachian.
The Neoproterozoic world was very different from this one. Earth had just emerged from the Cryogenian, the time of Snowball (or Slushball) Earth, when glaciers were found even at very low latitudes. The seafloor was lined with microbial or algal mats, and Ediacarans either stuck to the mat, burrowed under it, or grazed on it. These colonies of life made quite a concentration of energy, better known as food, so when lifeforms developed teeth, Ediacarans quickly went extinct. The base of the Cambrian is not really an Explosion of Life. It’s more like the explosive start of a biological arms race, when teeth, armor, and burrowing into the sediments were the new fashion of the day.
There were a variety of forms preserved, to be later found in North Carolina. Pteridinium was a stalked organism with vanes spread out from the stalk. The stalk had a bulblike body part holding it to the substrate, called the holdfast. Those vanes looked like an old-fashioned air mattress with ridges. Aspidella was a fairly odd looking circular fossil, finally recognized as the scar where a holdfast was pulled loose. Tony Furr brought us a specimen that we worked to identify, finally, as similar to Swartpuntia, known from Namibia. We had several papers on these, but the free ones will be downloaded to your computer if you click here: Carolina Geological Society papers 2006 (PDF).
Trish Weaver and I were brought into this research by Tony Furr and Ruffin Tucker, a couple of amateur fossil collectors. Ruffin has probably found more Ediacara than anyone else in North Carolina’s history, amateur or pro. We had a running joke that the most likely place to find Ediacaran fossils in North Carolina was the trunk of Ruffin’s car. It took three of us to haul the slab in question from the trunk of Ruffin’s car.
Ruffin’s slab is now on display in the Nature Research Center on the third floor. The forms on the slab had originally been interpreted as feeding traces, Oldhamia recta, by Adolph Seilacher, the brilliant originator of ichnology and master of all fossils Proterozoic. The traces didn’t intersect, so Seilacher argued that they had enough of a neurosystem to avoid each other and avoid their earlier feeding tunnels. But looking at Ruffin’s slab, I got the sense that the tubes/tunnels were all aligned, which argued for an animal that stuck up into the water rather than burrowing under the mat. If these were feeding traces, these animals had some way of communicating, unless they weren’t feeding traces at all…..
Even more interesting is research into the behavior of animals that left traces behind, known as ichnology. Trace fossils include the burrows, tracks, trails, marks and endangered feces left behind in the fossil record. Our colleague Tony Martin of Emory University is the go-to guy for that, so Trish and I invited Tony into the mix. I only wish Tony had been there earlier, to help us manhandle it out of Ruffin’s trunk.
I mapped Ruffin’s slab, as seen at the top of this blog, then we measured the orientation of about 400 different Oldhamia recta. Then we obtained the original type specimens from the Yale Peabody Musuem and mapped and measured those. The final story was that our measurements were consistent with a population on Ruffin’s slab being aligned by current, and another population torn loose by current and rolling loose. Folds in Ruffin’s slab were rucked-up microbial mat, just like a rug on a hardwood floor. Then the kicker: the Oldhamia on the Yale Peabody specimens were even more aligned than Ruffin’s.
So the fossils on Ruffin’s slab were not feeding traces, but tube organisms knocked down by current. We published it in Precambrian Geology. The team of mineralogist/geochemist, ichnologist and invertebrate paleontologist had successfully re-interpreted one of Adolph Seilacher’s fossils, and the hard-rock geologist was somehow first author on a paleo paper. None of it would be possible without Tony Furr and Ruffin and their donations to the Fossil Collection.
But that was just the beginning. There are other features on that slab that are interesting. The wormy things/burrowers/tunnelers left traces with levees on the side where they muscled through the sediment. You can estimate their size from width and the turns in the trace. There’s one great big one plowed through the things we called “bunches of grapes”. And Charlotte is expanding outward into the neighboring counties, so who knows what will come to light?