A whole new microscopic world

by Bianca Harrison (University of Cape Town)

Micropalaeontology opens up a whole new world to be observed that is not visible with the naked eye. These are fossils of mainly single-celled organisms smaller than 1mm which is smaller than a pin head! When searching for these tiny fossils underneath the microscope, a sense of awe overcomes you as you realise that YOU are the first person to observe what the rock has hidden away for millions or even billions of years. But I am getting ahead of myself…

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Figure 1. Image of an acritarch (microfossil) Credit: Malgorzata Moczydlowska-Vidal

 

I am a first year MSc student in South Africa and had the opportunity to travel to Uppsala, Sweden to work with Malgorzata Moczydlowska-Vidal at Uppsala University. This was a tremendous opportunity to learn how to process rock samples for microfossils in a world-renowned scientist’s lab. This training was extremely vital as I plan to compare microfossils of the Vanrhynsdorp Group, South Africa and the Vestertana Group, Finnmark, northern Norway. These Groups are of significance as they span the Ediacaran-Cambrian boundary (~541 million years ago). The study will contribute to understanding the nature, behavior and diversity of microorganisms before and during the “Cambrian explosion” – a geologically sudden event when complex marine organisms become abundant for the first time. Microfossils are useful as biostratigraphic markers as the presence of different species at different intervals can pinpoint time periods and correlate rock formations from different locations around the world.

With all this in mind, I embarked on a week long journey in Malgorzata’s lab where we dissolved rock samples from South Africa. The fun side of lab work are the cool outfits you get to wear! Safety is of utmost importance but whoever said you can’t look good while doing it?

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Figure 2. Safety gear for working with HF under the Fume hood

On a more serious note, hydrofluoric (HF) acid is used as it dissolves silica (a large component in rocks) whereas organic compounds are resistant and do not dissolve. However, HF acid is also capable of dissolving glass and human tissue, so extreme care is used when handling the acid. In light of this, a small disclaimer is needed – do not try this at home! Scientists have special labs and equipment that allow them to work with these dangerous chemicals. However, the exciting part begins once the rock is dissolved and this can take ~2 days.

Once the sample is dissolved, the moment of truth arrives. The bottom-line: the darker the residue, the higher the organic content in the rock and the higher the chance of fossils. From there, the samples are washed thoroughly, boiled in hydrochloric acid to dissolve other minerals, filtered and mounted onto microscope slides. Identifying microfossils underneath the microscope can be tricky but there are a few key things to look out for: 1) sharp boundary of the object, 2) shape, and 3) colour. Depending on the age of the rocks and the species of microfossils, the specimens can range from looking like wrinkled blobs to beautifully complex structures. Regardless, the information they can reveal is invaluable. At the moment, I am still in the preliminary stages and learning all I can about microfossil work before I find any of my own specimens! Wish me luck as I embark into this ‘small’ and exciting world!

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Figure 3. A – Filtering the sample to obtain the correct size interval (>20 microns). B – Filtered sample with organic material (the dark clump at the bottom of the tube) being cleaned with acetone before being ready for mounting.

 

Enigmatic animals that lived 540 million years ago

by Zhiji Ou

The Cambrian explosion is one of the most well known events in Earth history, during which most major modern metazoan phyla appeared. Prior to the Cambrian explosion (namely in the Precambrian, the largest time span in Earth’s history) animals were scarce, skeleton-less, and weird looking. Although a few of them may show similar morphology to modern sponges, comb jellies and jellyfish, the majority represent unknown clades which are believed to have died out. During the transition from the Precambrian to the Cambrian, there were quite a few fossils, which look similar to some creatures living today. They are not easily placed in the tree of life tree just because of their simple appearances. One of these enigmatic organisms is called Sabellidites cambriensis.

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Body fossil of Sabellidites, photo; Malgorzata Moczydlowska Vidal

 Sabellidites was a tubular animal that lived about 542 million years ago. It has a pure-organic tube, giving it a black and sometimes shiny look. The surface of the tube is either smooth, with fine furrows or wrinkles. The characteristically wrinkled tubes are 0.2–3.0 millimeters wide and up to 16 cm long. But flattening always happened during burying, so most of the Sabellidites fossils have a ribbon-like rather than a tubular appearance.

This fossil was first found by a former Soviet Union scientist named Yanishevskii in 1925 in Petrograd, USSR. Later on, researchers claimed the occurrences of Sabellidites in other parts of the East European Platform, China, Serbia, Canada and northern Scandinavia. Contemporaneous to Sabellidites are other diverse animals, which have a hard bio-mineralizing skeleton, such as Sinotubulites, Cloudina, Namacalathus and Nama-poikia. Quite different from them, Sabellidites is unique for its organic tube The tube has discrete layers composed of differently orientated fibers embedded in an amorphous matrix. What´s more, evidence from biogeochemistry shows that this organic tube contains β chitin. The closest animal, which has both β chitin and similar morphology of the tube, is the family Siboglinidae. Thus some scientists group Sabellidites as an extinct member of the family Siboglinidae within the phylum Annelida.

Siboglinidae, also called beard worms, are composed of about 100 tubular species, which live in sediments at ocean depths from 100 to 10,000 meters. Most siboglinids are less than 1 millimeter in diameter but 10–75 centimeters in length. The tubes are often clustered together in large colonies. The worms have a complex closed circulatory system and a well-developed nervous system, but as adults, siboglinids lack a functional mouth, gut and anus. But that does not mean adult siboglinids can survive without assimilating any nutrients. These worms derive energy from a special storage organ, which is called a trophosome. Tons of microbes live here and produce enough organic matter for their hosts. Siboglinids are dioecious, which means each individual is either male or female. The fertilized eggs hatch to produce small paramecium-like larvae. But after they grow up, they lose the ability of free movement and become sessile.

 

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Scientists discussing Sabellidites (left: Anette Högström from Tromsø University Museum; right: Malgorzata Moczydlowska Vidal from Uppsala University).

However, there are still a lot of unsolved puzzles and debates about this fossil. Recently, scientists from all over the world gathered in Tromsø (Norway) and Uppsala (Sweden) to study and discuss the morphology, phylogeny, taphonomy and palaeo-ecology of Sabellidites from the Digermulen Peninsula and the East European Platform.