Ancient Seaweed Fossils from Mongolia
Research conducted by a team of international scientists from Mongolia, Japan and the University of Wisconsin-Milwaukee (United States), have identified two new species of ancient multi-cellular marine algae from a newly discovered Burgess Shale Type deposit located in the Zavkhan Basin of Zavkhan Province (western Mongolia). The fossils are exceptionally rare and date from approximately 555 million years ago (Ediacaran geological period), they are helping researchers to pinpoint the development of complex lifeforms from the Kingdom Plantae, the ancestors of all plants that exist today. A paper on the research into the thin shale beds (representing the Zuun-Arts biota), has been published in the online, open access journal “Scientific Reports”.
Lead Author of the Study Associate Professor Stephen Dornbos Holds One of the Fossil Specimens
-Picture Credit: University of Wisconsin-Milwaukee
The preservation of soft-bodied organisms such as these remains of algae are exceptionally rare in the fossil record. One such method of preservation is carbonisation in fine-grained strata. These deposits of exceptional preservation are referred to as Burgess Shale Type deposits, after the famous Cambrian site in British Columbia. Burgess Shale Type deposits preserving the remains of organisms that lived before the Burgess Shales themselves were formed, can provide scientists with a tantalising glimpse into marine life prior to the evolution of animals with hard bodies such as exoskeletons and shells, but only a handful of pre-Cambrian (Ediacaran) Burgess Shale Type deposits are known. The research team were exploring ancient marine rocks in western Mongolia when the thin black shales containing carbonised remnants of the prehistoric seaweeds were discovered.
Two species of multi-cellular marine algae have been identified, the most common fossils representing the newly described Chinggiskhaania bifurcata. The other species, known from just three fossil specimens has been named Zuunartsphyton delicatum.
A Cross Polarised Light Image of C. bifurcata
Picture Credit: University of Wisconsin-Milwaukee
Under polarised light the structure of the fine filaments of the ancient seaweed can be clearly seen. Contrast this picture with the photograph of Stephen Dornbos holding a specimen. The fossils consist of aluminosilicate clay minerals and some carbon, just like the Burgess Shale fossils, and as such, spotting fossils is a very difficult task. Natural light has to strike the fossil at the correct angle, otherwise the specimen cannot be distinguished from the surrounding matrix.
Commenting on the discovery of the Zuun-Arts biota, Associate Professor Stephen Dornbos stated:
“This discovery helps tell us more about life in a period that is relatively undocumented. It can help us correlate the changes in life forms with what we know about the Earth’s ancient environments. It is a major evolutionary step toward life as we know it today.”
Extremely Hard to Classify
Burgess Shale Type fossils dating from the Proterozoic Eon usually are classified as one of two categories, algae, like seaweed, which is the case of the Zuun-Arts biota, or the remains of extinct types of organisms so unlike living organisms today, that identifying what they might have been like is very difficult to do. As a result, interpretation of Ediacaran fossil material is a very controversial area of palaeontology.
Explaining this problem, Stephen Dornbos commented:
“If you find a fossil from this time frame, you really need strong support for your interpretation of what it was. The further back you go in geologic time, the more contested the fossil interpretations are.”
An Illustration Depicting Life in the Ediacaran Geological Period
Picture Credit: John Sibbick