Exploring the Dawn of Animal Life

Researchers possibly identify first occurrence of digestive tracts in the fossil record using electron microscopy and tomographic X-ray imaging

Dr. James Schiffbauer, University of Missouri

Dr. James Schiffbauer and his team at the University of Missouri, USA, focus their research on how accurately they can interpret the history of life from the fossil record. Dr. Schiffbauer is particularly interested in complex multicellular fossils from the dawn of animal life at the Ediacaran–Cambrian transition (~550–539 million years ago). His work relies heavily on advanced microscopy methods – including scanning electron microscopy and tomographic X-ray imaging.

Dr. Schiffbauer recently published in Nature Communications an article describing tomographic analyses of fossils from the Wood Canyon Formation (Nevada, USA) which revealed recognizable soft tissues within their external tubes. These data could be evidence of the earliest-known occurrence of digestive tracts.

We spoke with Dr. Schiffbauer and his assistant director, Dr. Tara Selly, who was also an author in the paper, about their research and recent publication.

Dr. Tara Selly, co-author on the paper, collecting samples at Mt. Dunfee, Nevada.

You used both electron microscopy and X-ray microscopy in this research article. Could you describe how each technology contributed to the published results?

Dr. Schiffbauer: At first, Tara and I were examining these tubular fossils in an effort to systematically describe them. These were relatively newly discovered fossils, and identifying them taxonomically was an important contribution. Thus, our initial use of X-ray microscopy on these fossils was to see the structure of their external tubes – which could be taxonomically informative. We could observe on the rocks that the fossils were preserved in three-dimensions; so, in order to better describe their morphology in a non-destructive manner, we used XRM to “see inside of the rock” – which is when we stumbled upon the soft tissues within the fossil tubes. Then, in an effort to better understand how these soft tissues were preserved, we unfortunately did need to prepare one of our samples destructively (via serial-grinding) which we then analyzed with SEM and EDS.

Dr. Selly: Once we had identified the soft-tissues within our fossil sample we continued to use X-ray microscopy for exploratory analysis of these materials to determine whether this structure was part of the fossil or an artifact. We used quick low-resolution scans to locate other soft-bodied structures and then performed high-resolution full scans to capture their detailed morphologies. To assess these datasets, we used Dragonfly (ORS) to segment and visualize our materials.

3D renders of cloudinomorph gut structure (red = external tube, orange = soft-tissue). Scale = 1mm. Render created using X-ray tomography.

Were there any results that were published in this paper that you found particularly exciting and/or pushed your research in a new direction?

Dr. Schiffbauer: Honestly, I think this whole paper is exciting. Sure – the “oldest guts yet discovered” part is certainly exciting, but from where we started with this project to where it ended up going and the story these fossils told – those are the more exciting parts in my opinion. We started out with a goal of simply systematically classifying these tubular fossils to better place them in a global context, and we discovered something that may really much better place them in a phylogenetic/evolutionary context. The origin of animals has been an elusive story, and the data we show here may help to connect previously unconnected dots.

Cloudinomorph 3D volume render showing ribbon-like gut (top) of Wood Canyon Formation, Nevada fossil (bottom). Scale = 1mm. Render created using X-ray tomography.

Dr. Selly: Building off of Jim’s response, this study is also exciting as it gives more substantial evidence that Ediacarans were not just “simple sac-like forms”. Molecular clock data tells us that bilaterians should be present at this time, but our evidence has mostly been limited to trace fossils at this time. Now, with this discovery, we can confirm that Ediacaran cloudinomorphs were indeed bilaterian animals.

Cloudinomorph worm reconstruction with cross-section of digestive gut-tract. Photo Credit: Stacy Turpin Cheavens, University of Missouri.

What research are you currently focused on now? Will you be using similar microscopy techniques?

Dr. Schiffbauer: My work is mostly focused on taphonomic processes, or those that are responsible for fossilization. As opposed to the shells and bones that dominate the fossil record, my group most commonly studies the rarer instances of soft-tissue preservation – which require external/environmental mineralization processes in order to enter the fossil record. This kind of work lends itself well to the timeframe when animals first evolved, because they hadn’t yet “figured out” how to biologically construct shells. To answer the questions that we normally ask, microscopy techniques such as SEM and XRM are nearly a must have in your tool belt.

Dr. Selly: As a former student of Jim’s, I too am interested in taphonomic processes. In my current research, I investigate these same questions but, rather than analyzing fossils, I use modern organisms to track the progression of decay, known as experimental taphonomy. Recently, I have been using the XRM to develop novel methods for assessing experimental taphonomic data using staining techniques and volumetric measurements for non-destructive analysis.

Learn More

Read the full article “Discovery of bilaterian-type through-guts in cloudinomorphs from the terminal Ediacaran Period” in Nature Communications

Learn about ZEISS X-ray tomography solutions

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